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Sunday, June 28, 2020

Battle of Gettysburg

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Battle of Gettysburg
Part of the Eastern Theater of the American Civil War
Thure de Thulstrup - L. Prang and Co. - Battle of Gettysburg - Restoration by Adam Cuerden.jpg
The Battle of Gettysburg by Thure de Thulstrup
DateJuly 1–3, 1863
Location 39.811°N 77.225°WCoordinates: 39.811°N 77.225°W
Result Union victory
Belligerents
 United States  Confederate States
Commanders and leaders
United States George G. Meade
United States John F. Reynolds 
United States Winfield S. Hancock
United States Daniel Sickles
United States George Sykes
United States John Sedgwick
United States Oliver Otis Howard
United States Henry Warner Slocum
United States Alfred Pleasonton
United States Robert O. Tyler
United States Henry Jackson Hunt
Confederate States of America Robert E. Lee
Confederate States of America James Longstreet
Confederate States of America Richard S. Ewell
Confederate States of America A. P. Hill
Confederate States of America J.E.B. Stuart
Units involved
Army of the Potomac Army of Northern Virginia
Strength
104,256 ("present for duty") 71,000–75,000 (estimated)
Casualties and losses
23,049 total
(3,155 killed;
14,529 wounded;
5,365 captured/missing)
23,000–28,000 (estimated)
Northern Virginia, Maryland and Pennsylvania (1861–1865)
 
Gettysburg Campaign, (1863)
 
Battlefield of Gettysburg, (1863)
 
The Battle of Gettysburg was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania, by Union and Confederate forces during the American Civil War. The battle involved the largest number of casualties of the entire war and is often described as the war's turning point. Union Maj. Gen. George Meade's Army of the Potomac defeated attacks by Confederate Gen. Robert E. Lee's Army of Northern Virginia, halting Lee's invasion of the North.

After his success at Chancellorsville in Virginia in May 1863, Lee led his army through the Shenandoah Valley to begin his second invasion of the North—the Gettysburg Campaign. With his army in high spirits, Lee intended to shift the focus of the summer campaign from war-ravaged northern Virginia and hoped to influence Northern politicians to give up their prosecution of the war by penetrating as far as Harrisburg, Pennsylvania, or even Philadelphia. Prodded by President Abraham Lincoln, Maj. Gen. Joseph Hooker moved his army in pursuit, but was relieved of command just three days before the battle and replaced by Meade. 

Elements of the two armies initially collided at Gettysburg on July 1, 1863, as Lee urgently concentrated his forces there, his objective being to engage the Union army and destroy it. Low ridges to the northwest of town were defended initially by a Union cavalry division under Brig. Gen. John Buford, and soon reinforced with two corps of Union infantry. However, two large Confederate corps assaulted them from the northwest and north, collapsing the hastily developed Union lines, sending the defenders retreating through the streets of the town to the hills just to the south.

On the second day of battle, most of both armies had assembled. The Union line was laid out in a defensive formation resembling a fishhook. In the late afternoon of July 2, Lee launched a heavy assault on the Union left flank, and fierce fighting raged at Little Round Top, the Wheatfield, Devil's Den, and the Peach Orchard. On the Union right, Confederate demonstrations escalated into full-scale assaults on Culp's Hill and Cemetery Hill. All across the battlefield, despite significant losses, the Union defenders held their lines.

On the third day of battle, fighting resumed on Culp's Hill, and cavalry battles raged to the east and south, but the main event was a dramatic infantry assault by 12,500 Confederates against the center of the Union line on Cemetery Ridge, known as Pickett's Charge. The charge was repulsed by Union rifle and artillery fire, at great loss to the Confederate army.

Lee led his army on a torturous retreat back to Virginia. Between 46,000 and 51,000 soldiers from both armies were casualties in the three-day battle, the most costly in US history.

On November 19, President Lincoln used the dedication ceremony for the Gettysburg National Cemetery to honor the fallen Union soldiers and redefine the purpose of the war in his historic Gettysburg Address.

Background

Military situation

Gettysburg Campaign (through July 3); cavalry movements shown with dashed lines
  Confederate
  Union
 
This 1863 oval-shaped map depicts Gettysburg Battlefield during July 1–3, 1863, showing troop and artillery positions and movements, relief hachures, drainage, roads, railroads, and houses with the names of residents at the time of the Battle of Gettysburg.
 
A Harper's Weekly illustration showing Confederate troops escorting captured African American civilians south into slavery. En route to Gettysburg, the Army of Northern Virginia kidnapped approximately 40 black civilians and sent them south into slavery.
 
Shortly after the Army of Northern Virginia won a major victory over the Army of the Potomac at the Battle of Chancellorsville (April 30 – May 6, 1863), Robert E. Lee decided upon a second invasion of the North (the first was the unsuccessful Maryland Campaign of September 1862, which ended in the bloody Battle of Antietam). Such a move would upset the Union's plans for the summer campaigning season and possibly reduce the pressure on the besieged Confederate garrison at Vicksburg. The invasion would allow the Confederates to live off the bounty of the rich Northern farms while giving war-ravaged Virginia a much-needed rest. In addition, Lee's 72,000-man army could threaten Philadelphia, Baltimore, and Washington, and possibly strengthen the growing peace movement in the North.

Initial movements to battle

Thus, on June 3, Lee's army began to shift northward from Fredericksburg, Virginia. Following the death of Thomas J. "Stonewall" Jackson, Lee reorganized his two large corps into three new corps, commanded by Lt. Gen. James Longstreet (First Corps), Lt. Gen. Richard S. Ewell (Second), and Lt. Gen. A.P. Hill (Third); both Ewell and Hill, who had formerly reported to Jackson as division commanders, were new to this level of responsibility. The Cavalry Division remained under the command of Maj. Gen. J.E.B. Stuart.

The Union Army of the Potomac, under Maj. Gen. Joseph Hooker, consisted of seven infantry corps, a cavalry corps, and an Artillery Reserve, for a combined strength of more than 100,000 men.

The first major action of the campaign took place on June 9 between cavalry forces at Brandy Station, near Culpeper, Virginia. The 9,500 Confederate cavalrymen under Stuart were surprised by Maj. Gen. Alfred Pleasonton's combined arms force of two cavalry divisions (8,000 troopers) and 3,000 infantry, but Stuart eventually repulsed the Union attack. The inconclusive battle, the largest predominantly cavalry engagement of the war, proved for the first time that the Union horse soldier was equal to his Southern counterpart.

By mid-June, the Army of Northern Virginia was poised to cross the Potomac River and enter Maryland. After defeating the Union garrisons at Winchester and Martinsburg, Ewell's Second Corps began crossing the river on June 15. Hill's and Longstreet's corps followed on June 24 and 25. Hooker's army pursued, keeping between Washington, D.C. and Lee's army. The Union army crossed the Potomac from June 25 to 27.

Lee gave strict orders for his army to minimize any negative impacts on the civilian population. Food, horses, and other supplies were generally not seized outright, although quartermasters reimbursing Northern farmers and merchants with Confederate money were not well received. Various towns, most notably York, Pennsylvania, were required to pay indemnities in lieu of supplies, under threat of destruction. During the invasion, the Confederates seized some 40 northern African Americans. A few of them were escaped fugitive slaves, but most were freemen; all were sent south into slavery under guard.

On June 26, elements of Maj. Gen. Jubal Early's division of Ewell's Corps occupied the town of Gettysburg after chasing off newly raised Pennsylvania militia in a series of minor skirmishes. Early laid the borough under tribute, but did not collect any significant supplies. Soldiers burned several railroad cars and a covered bridge, and destroyed nearby rails and telegraph lines. The following morning, Early departed for adjacent York County.

Meanwhile, in a controversial move, Lee allowed J.E.B. Stuart to take a portion of the army's cavalry and ride around the east flank of the Union army. Lee's orders gave Stuart much latitude, and both generals share the blame for the long absence of Stuart's cavalry, as well as for the failure to assign a more active role to the cavalry left with the army. Stuart and his three best brigades were absent from the army during the crucial phase of the approach to Gettysburg and the first two days of battle. By June 29, Lee's army was strung out in an arc from Chambersburg (28 miles (45 km) northwest of Gettysburg) to Carlisle (30 miles (48 km) north of Gettysburg) to near Harrisburg and Wrightsville on the Susquehanna River.

In a dispute over the use of the forces defending the Harpers Ferry garrison, Hooker offered his resignation, and Abraham Lincoln and General-in-Chief Henry W. Halleck, who were looking for an excuse to rid themselves of him, immediately accepted. They replaced Hooker early on the morning of June 28 with Maj. Gen. George Gordon Meade, then commander of the V Corps.

On June 29, when Lee learned that the Army of the Potomac had crossed the Potomac River, he ordered a concentration of his forces around Cashtown, located at the eastern base of South Mountain and eight miles (13 km) west of Gettysburg. On June 30, while part of Hill's Corps was in Cashtown, one of Hill's brigades, North Carolinians under Brig. Gen. J. Johnston Pettigrew, ventured toward Gettysburg. In his memoirs, Maj. Gen. Henry Heth, Pettigrew's division commander, claimed that he sent Pettigrew to search for supplies in town—especially shoes.

When Pettigrew's troops approached Gettysburg on June 30, they noticed Union cavalry under Brig. Gen. John Buford arriving south of town, and Pettigrew returned to Cashtown without engaging them. When Pettigrew told Hill and Heth what he had seen, neither general believed that there was a substantial Union force in or near the town, suspecting that it had been only Pennsylvania militia. Despite General Lee's order to avoid a general engagement until his entire army was concentrated, Hill decided to mount a significant reconnaissance in force the following morning to determine the size and strength of the enemy force in his front. Around 5 a.m. on Wednesday, July 1, two brigades of Heth's division advanced to Gettysburg.

Opposing forces

Union

Key commanders (Army of the Potomac)
The Army of the Potomac, initially under Maj. Gen. Joseph Hooker (Maj. Gen. George Meade replaced Hooker in command on June 28), consisted of more than 100,000 men in the following organization:
During the advance on Gettysburg, Maj. Gen. Reynolds was in operational command of the left, or advanced, wing of the Army, consisting of the I, III, and XI Corps. Note that many other Union units (not part of the Army of the Potomac) were actively involved in the Gettysburg Campaign, but not directly involved in the Battle of Gettysburg. These included portions of the Union IV Corps, the militia and state troops of the Department of the Susquehanna, and various garrisons, including that at Harpers Ferry.

Confederate

Key commanders (Army of Northern Virginia)
In reaction to the death of Lt. Gen. Thomas J. "Stonewall" Jackson after Chancellorsville, Lee reorganized his Army of Northern Virginia (75,000 men) from two infantry corps into three.

First day of battle

Overview map of the first day of the Battle of Gettysburg, July 1, 1863

Herr Ridge, McPherson Ridge and Seminary Ridge

Anticipating that the Confederates would march on Gettysburg from the west on the morning of July 1, Buford laid out his defenses on three ridges west of the town: Herr Ridge, McPherson Ridge and Seminary Ridge. These were appropriate terrain for a delaying action by his small cavalry division against superior Confederate infantry forces, meant to buy time awaiting the arrival of Union infantrymen who could occupy the strong defensive positions south of town at Cemetery Hill, Cemetery Ridge, and Culp's Hill. Buford understood that if the Confederates could gain control of these heights, Meade's army would have difficulty dislodging them.

First shot monument

Confederate General Henry Heth's division advanced with two brigades forward, commanded by Brig. Gens. James J. Archer and Joseph R. Davis. They proceeded easterly in columns along the Chambersburg Pike. Three miles (5 km) west of town, about 7:30 a.m. on July 1, the two brigades met light resistance from vedettes of Union cavalry, and deployed into line. According to lore, the Union soldier to fire the first shot of the battle was Lt. Marcellus Jones. Lt. Jones later returned to Gettysburg, in 1886 erecting a monument marking the spot where he fired the first shot. Eventually, Heth's men reached dismounted troopers of Col. William Gamble's cavalry brigade, who raised determined resistance and delaying tactics from behind fence posts with fire from their breechloading carbines. Still, by 10:20 a.m., the Confederates had pushed the Union cavalrymen east to McPherson Ridge, when the vanguard of the I Corps (Maj. Gen. John F. Reynolds) finally arrived.

North of the pike, Davis gained a temporary success against Brig. Gen. Lysander Cutler's brigade but was repulsed with heavy losses in an action around an unfinished railroad bed cut in the ridge. South of the pike, Archer's brigade assaulted through Herbst (also known as McPherson's) Woods. The Union Iron Brigade under Brig. Gen. Solomon Meredith enjoyed initial success against Archer, capturing several hundred men, including Archer himself.

General Reynolds was shot and killed early in the fighting while directing troop and artillery placements just to the east of the woods. Shelby Foote wrote that the Union cause lost a man considered by many to be "the best general in the army." Maj. Gen. Abner Doubleday assumed command. Fighting in the Chambersburg Pike area lasted until about 12:30 p.m. It resumed around 2:30 p.m., when Heth's entire division engaged, adding the brigades of Pettigrew and Col. John M. Brockenbrough.

As Pettigrew's North Carolina Brigade came on line, they flanked the 19th Indiana and drove the Iron Brigade back. The 26th North Carolina (the largest regiment in the army with 839 men) lost heavily, leaving the first day's fight with around 212 men. By the end of the three-day battle, they had about 152 men standing, the highest casualty percentage for one battle of any regiment, North or South. Slowly the Iron Brigade was pushed out of the woods toward Seminary Ridge. Hill added Maj. Gen. William Dorsey Pender's division to the assault, and the I Corps was driven back through the grounds of the Lutheran Seminary and Gettysburg streets.

As the fighting to the west proceeded, two divisions of Ewell's Second Corps, marching west toward Cashtown in accordance with Lee's order for the army to concentrate in that vicinity, turned south on the Carlisle and Harrisburg roads toward Gettysburg, while the Union XI Corps (Maj. Gen. Oliver O. Howard) raced north on the Baltimore Pike and Taneytown Road. By early afternoon, the Union line ran in a semicircle west, north, and northeast of Gettysburg.

However, the Union did not have enough troops; Cutler, whose brigade was deployed north of the Chambersburg Pike, had his right flank in the air. The leftmost division of the XI Corps was unable to deploy in time to strengthen the line, so Doubleday was forced to throw in reserve brigades to salvage his line.

Around 2 p.m., the Confederate Second Corps divisions of Maj. Gens. Robert E. Rodes and Jubal Early assaulted and out-flanked the Union I and XI Corps positions north and northwest of town. The Confederate brigades of Col. Edward A. O'Neal and Brig. Gen. Alfred Iverson suffered severe losses assaulting the I Corps division of Brig. Gen. John C. Robinson south of Oak Hill. Early's division profited from a blunder by Brig. Gen. Francis C. Barlow, when he advanced his XI Corps division to Blocher's Knoll (directly north of town and now known as Barlow's Knoll); this represented a salient in the corps line, susceptible to attack from multiple sides, and Early's troops overran Barlow's division, which constituted the right flank of the Union Army's position. Barlow was wounded and captured in the attack.

As Union positions collapsed both north and west of town, Gen. Howard ordered a retreat to the high ground south of town at Cemetery Hill, where he had left the division of Brig. Gen. Adolph von Steinwehr in reserve. Maj. Gen. Winfield S. Hancock assumed command of the battlefield, sent by Meade when he heard that Reynolds had been killed. Hancock, commander of the II Corps and Meade's most trusted subordinate, was ordered to take command of the field and to determine whether Gettysburg was an appropriate place for a major battle. Hancock told Howard, "I think this the strongest position by nature upon which to fight a battle that I ever saw." When Howard agreed, Hancock concluded the discussion: "Very well, sir, I select this as the battle-field." Hancock's determination had a morale-boosting effect on the retreating Union soldiers, but he played no direct tactical role on the first day.

General Lee understood the defensive potential to the Union if they held this high ground. He sent orders to Ewell that Cemetery Hill be taken "if practicable." Ewell, who had previously served under Stonewall Jackson, a general well known for issuing peremptory orders, determined such an assault was not practicable and, thus, did not attempt it; this decision is considered by historians to be a great missed opportunity.

The first day at Gettysburg, more significant than simply a prelude to the bloody second and third days, ranks as the 23rd biggest battle of the war by number of troops engaged. About one quarter of Meade's army (22,000 men) and one third of Lee's army (27,000) were engaged.

Second day of battle

Robert E. Lee's plan for July 2, 1863

Plans and movement to battle

Throughout the evening of July 1 and morning of July 2, most of the remaining infantry of both armies arrived on the field, including the Union II, III, V, VI, and XII Corps. Two of Longstreet's divisions were on the road: Brig. Gen. George Pickett, had begun the 22 mile (35 km) march from Chambersburg, while Brig. Gen. E. M. Law had begun the march from Guilford. Both arrived late in the morning. Law completed his 28-mile (45 km) march in eleven hours.

The Union line ran from Culp's Hill southeast of the town, northwest to Cemetery Hill just south of town, then south for nearly two miles (3 km) along Cemetery Ridge, terminating just north of Little Round Top. Most of the XII Corps was on Culp's Hill; the remnants of I and XI Corps defended Cemetery Hill; II Corps covered most of the northern half of Cemetery Ridge; and III Corps was ordered to take up a position to its flank. The shape of the Union line is popularly described as a "fishhook" formation.

The Confederate line paralleled the Union line about a mile (1,600 m) to the west on Seminary Ridge, ran east through the town, then curved southeast to a point opposite Culp's Hill. Thus, the Union army had interior lines, while the Confederate line was nearly five miles (8 km) long.

Lee's battle plan for July 2 called for a general assault of Meade's positions. On the right, Longstreet's First Corps was to position itself to attack the Union left flank, facing northeast astraddle the Emmitsburg Road, and to roll up the Union line. The attack sequence was to begin with Maj. Gens. John Bell Hood's and Lafayette McLaws's divisions, followed by Maj. Gen. Richard H. Anderson's division of Hill's Third Corps.

On the left, Lee instructed Ewell to position his Second Corps to attack Culp's Hill and Cemetery Hill when he heard the gunfire from Longstreet's assault, preventing Meade from shifting troops to bolster his left. Though it does not appear in either his or Lee's Official Report, Ewell claimed years later that Lee had changed the order to simultaneously attack, calling for only a "diversion", to be turned into a full-scale attack if a favorable opportunity presented itself.

Lee's plan, however, was based on faulty intelligence, exacerbated by Stuart's continued absence from the battlefield. Though Lee personally reconnoitered his left during the morning, he did not visit Longstreet's position on the Confederate right. Even so, Lee rejected suggestions that Longstreet move beyond Meade's left and attack the Union flank, capturing the supply trains and effectively blocking Meade's escape route.

Lee did not issue orders for the attack until 11:00 a.m. About noon, General Anderson's advancing troops were discovered by General Sickles' outpost guard and the Third Corps–upon which Longstreet's First Corps was to form–did not get into position until 1:00 p.m.

Hood and McLaws, after their long march, were not yet in position and did not launch their attacks until just after 4 p.m. and 5 p.m., respectively.

Attacks on the Union left flank

Overview map of the second day of the Battle of Gettysburg, July 2, 1863
 
As Longstreet's left division, under Maj. Gen. Lafayette McLaws, advanced, they unexpectedly found Maj. Gen. Daniel Sickles's III Corps directly in their path. Sickles had been dissatisfied with the position assigned him on the southern end of Cemetery Ridge. Seeing ground better suited for artillery positions a half mile (800 m) to the west— centered at the Sherfy farm's Peach Orchard—he violated orders and advanced his corp to the slightly higher ground along the Emmitsburg Road, moving away from Cemetery Ridge. The new line ran from Devil's Den, northwest to the Peach Orchard, then northeast along the Emmitsburg Road to south of the Codori farm. This created an untenable salient at the Peach Orchard; Brig. Gen. Andrew A. Humphreys's division (in position along the Emmitsburg Road) and Maj. Gen. David B. Birney's division (to the south) were subject to attacks from two sides and were spread out over a longer front than their small corps could defend effectively. The Confederate artillery was ordered to open fire at 3:00 p.m. After failing to attend a meeting at this time of Meade's corps commanders, Meade rode to Sickles' position and demanded an explanation of the situation. Knowing a Confederate attack was imminent and a retreat would be endangered, Meade refused Sickles' offer to withdraw.

Meade was forced to send 20,000 reinforcements: the entire V Corps, Brig. Gen. John C. Caldwell's division of the II Corps, most of the XII Corps, and portions of the newly arrived VI Corps. Hood's division moved more to the east than intended, losing its alignment with the Emmitsburg Road, attacking Devil's Den and Little Round Top. McLaws, coming in on Hood's left, drove multiple attacks into the thinly stretched III Corps in the Wheatfield and overwhelmed them in Sherfy's Peach Orchard. McLaws's attack eventually reached Plum Run Valley (the "Valley of Death") before being beaten back by the Pennsylvania Reserves division of the V Corps, moving down from Little Round Top. The III Corps was virtually destroyed as a combat unit in this battle, and Sickles's leg was amputated after it was shattered by a cannonball. Caldwell's division was destroyed piecemeal in the Wheatfield. Anderson's division, coming from McLaws's left and starting forward around 6 p.m., reached the crest of Cemetery Ridge, but could not hold the position in the face of counterattacks from the II Corps, including an almost suicidal bayonet charge by the 1st Minnesota regiment against a Confederate brigade, ordered in desperation by Hancock to buy time for reinforcements to arrive.

As fighting raged in the Wheatfield and Devil's Den, Col. Strong Vincent of V Corps had a precarious hold on Little Round Top, an important hill at the extreme left of the Union line. His brigade of four relatively small regiments was able to resist repeated assaults by Brig. Gen. Evander M. Law's brigade of Hood's division. Meade's chief engineer, Brig. Gen. Gouverneur K. Warren, had realized the importance of this position, and dispatched Vincent's brigade, an artillery battery, and the 140th New York to occupy Little Round Top mere minutes before Hood's troops arrived. The defense of Little Round Top with a bayonet charge by the 20th Maine, ordered by Col. Joshua L. Chamberlain but possibly led by Lt. Holman S. Melcher, was one of the most fabled episodes in the Civil War and propelled Col. Chamberlain into prominence after the war.

Attacks on the Union right flank

Union breastworks on Culp's Hill

Ewell interpreted his orders as calling only for a cannonade. His 32 guns, along with A. P. Hill's 55 guns, engaged in a two-hour artillery barrage at extreme range that had little effect. Finally, about six o'clock, Ewell sent orders to each of his division commanders to attack the Union lines in his front.

Maj. Gen. Edward "Allegheny" Johnson's Division "had not been pushed close to [Culp's Hill] in preparation for an assault, although one had been contemplated all day. It now had a full mile (1,600 m) to advance and Rock Creek had to be crossed. This could only be done at few places and involved much delay. Only three of Johnson's four brigades moved to the attack."  Most of the hill's defenders, the Union XII Corps, had been sent to the left to defend against Longstreet's attacks, leaving only a brigade of New Yorkers under Brig. Gen. George S. Greene behind strong, newly constructed defensive works. With reinforcements from the I and XI Corps, Greene's men held off the Confederate attackers, though giving up some of the lower earthworks on the lower part of Culp's Hill.

Early was similarly unprepared when he ordered Harry T. Hays' and Isaac E. Avery's Brigades to attack the Union XI Corps positions on East Cemetery Hill. Once started, fighting was fierce: Col. Andrew L. Harris of the Union 2nd Brigade, 1st Division, came under a withering attack, losing half his men. Avery was wounded early on, but the Confederates reached the crest of the hill and entered the Union breastworks, capturing one or two batteries. Seeing he was not supported on his right, Hays withdrew. His right was to be supported by Robert E. Rodes' Division, but Rodes—like Early and Johnson—had not been ordered up in preparation for the attack. He had twice as far to travel as Early; by the time he came in contact with the Union skirmish line, Early's troops had already begun to withdraw.

Jeb Stuart and his three cavalry brigades arrived in Gettysburg around noon but had no role in the second day's battle. Brig. Gen. Wade Hampton's brigade fought a minor engagement with newly promoted 23-year-old Brig. Gen. George Armstrong Custer's Michigan cavalry near Hunterstown to the northeast of Gettysburg.

Third day of battle

Overview map of the third day of the Battle of Gettysburg, July 3, 1863

Lee's plan

General Lee wished to renew the attack on Friday, July 3, using the same basic plan as the previous day: Longstreet would attack the Union left, while Ewell attacked Culp's Hill. However, before Longstreet was ready, Union XII Corps troops started a dawn artillery bombardment against the Confederates on Culp's Hill in an effort to regain a portion of their lost works. The Confederates attacked, and the second fight for Culp's Hill ended around 11 a.m. Harry Pfanz judged that, after some seven hours of bitter combat, "the Union line was intact and held more strongly than before."

Lee was forced to change his plans. Longstreet would command Pickett's Virginia division of his own First Corps, plus six brigades from Hill's Corps, in an attack on the Union II Corps position at the right center of the Union line on Cemetery Ridge. Prior to the attack, all the artillery the Confederacy could bring to bear on the Union positions would bombard and weaken the enemy's line.

Much has been made over the years of General Longstreet's objections to General Lee's plan. In his memoirs, Longstreet described their discussion as follows:
[Lee] rode over after sunrise and gave his orders. His plan was to assault the enemy's left centre by a column to be composed of McLaws's and Hood's divisions reinforced by Pickett's brigades. I thought that it would not do; that the point had been fully tested the day before, by more men, when all were fresh; that the enemy was there looking for us, as we heard him during the night putting up his defences; that the divisions of McLaws and Hood were holding a mile [1,600 m] along the right of my line against twenty thousand men, who would follow their withdrawal, strike the flank of the assaulting column, crush it, and get on our rear towards the Potomac River; that thirty thousand men was the minimum of force necessary for the work; that even such force would need close co-operation on other parts of the line; that the column as he proposed to organize it would have only about thirteen thousand men (the divisions having lost a third of their numbers the day before); that the column would have to march a mile [1,600 m] under concentrating battery fire, and a thousand yards [900 m] under long-range musketry; that the conditions were different from those in the days of Napoleon, when field batteries had a range of six hundred yards [550 m] and musketry about sixty yards [55 m]. He said the distance was not more than fourteen hundred yards [1280 m]. General Meade's estimate was a mile or a mile and a half [1.6 or 2.4 km] (Captain Long, the guide of the field of Gettysburg in 1888, stated that it was a trifle over a mile). He then concluded that the divisions of McLaws and Hood could remain on the defensive line; that he would reinforce by divisions of the Third Corps and Pickett's brigades, and stated the point to which the march should be directed. I asked the strength of the column. He stated fifteen thousand. Opinion was then expressed that the fifteen thousand men who could make successful assault over that field had never been arrayed for battle; but he was impatient of listening, and tired of talking, and nothing was left but to proceed.
The "High Water Mark" on Cemetery Ridge as it appears today. The monument to the 72nd Pennsylvania Volunteer Infantry Regiment ("Baxter's Philadelphia Fire Zouaves") appears at right, the Copse of Trees to the left.

The largest artillery bombardment of the war

Around 1 p.m., from 150 to 170 Confederate guns began an artillery bombardment that was probably the largest of the war. In order to save valuable ammunition for the infantry attack that they knew would follow, the Army of the Potomac's artillery, under the command of Brig. Gen. Henry Jackson Hunt, at first did not return the enemy's fire. After waiting about 15 minutes, about 80 Union cannons added to the din. The Army of Northern Virginia was critically low on artillery ammunition, and the cannonade did not significantly affect the Union position.

Pickett's Charge

Around 3 p.m., the cannon fire subsided, and 12,500 Southern soldiers stepped from the ridgeline and advanced the three-quarters of a mile (1,200 m) to Cemetery Ridge in what is known to history as "Pickett's Charge". As the Confederates approached, there was fierce flanking artillery fire from Union positions on Cemetery Hill and north of Little Round Top, and musket and canister fire from Hancock's II Corps. In the Union center, the commander of artillery had held fire during the Confederate bombardment (in order to save it for the infantry assault, which Meade had correctly predicted the day before), leading Southern commanders to believe the Northern cannon batteries had been knocked out. However, they opened fire on the Confederate infantry during their approach with devastating results. Nearly one half of the attackers did not return to their own lines.

Although the Union line wavered and broke temporarily at a jog called the "Angle" in a low stone fence, just north of a patch of vegetation called the Copse of Trees, reinforcements rushed into the breach, and the Confederate attack was repulsed. The farthest advance of Brig. Gen. Lewis A. Armistead's brigade of Maj. Gen. George Pickett's division at the Angle is referred to as the "High-water mark of the Confederacy". Union and Confederate soldiers locked in hand-to-hand combat, attacking with their rifles, bayonets, rocks and even their bare hands. Armistead ordered his Confederates to turn two captured cannons against Union troops, but discovered that there was no ammunition left, the last double canister shots having been used against the charging Confederates. Armistead was wounded shortly afterward three times.

Cavalry battles

There were two significant cavalry engagements on July 3. Stuart was sent to guard the Confederate left flank and was to be prepared to exploit any success the infantry might achieve on Cemetery Hill by flanking the Union right and hitting their trains and lines of communications. Three miles (5 km) east of Gettysburg, in what is now called "East Cavalry Field" (not shown on the accompanying map, but between the York and Hanover Roads), Stuart's forces collided with Union cavalry: Brig. Gen. David McMurtrie Gregg's division and Brig. Gen. Custer's brigade. A lengthy mounted battle, including hand-to-hand sabre combat, ensued. Custer's charge, leading the 1st Michigan Cavalry, blunted the attack by Wade Hampton's brigade, blocking Stuart from achieving his objectives in the Union rear.

Aftermath

Casualties

"The Harvest of Death": Union dead on the battlefield at Gettysburg, Pennsylvania, photographed July 5 or July 6, 1863, by Timothy H. O'Sullivan

The two armies suffered between 46,000 and 51,000 casualties, nearly one third of all total troops engaged, 28% of the Army of the Potomac and 37% of the Army of Northern Virginia. Union casualties were 23,055 (3,155 killed, 14,531 wounded, 5,369 captured or missing), while Confederate casualties are more difficult to estimate. Many authors have referred to as many as 28,000 Confederate casualties, and Busey and Martin's more recent 2005 work, Regimental Strengths and Losses at Gettysburg, documents 23,231 (4,708 killed, 12,693 wounded, 5,830 captured or missing). Nearly a third of Lee's general officers were killed, wounded, or captured. The casualties for both sides during the entire campaign were 57,225.

In addition to being the deadliest battle of the war, Gettysburg also had the highest number of generals killed in action. The Confederacy lost generals Paul Jones Semmes, William Barksdale, William Dorsey Pender, Richard Garnett, and Lewis Armistead, as well as J. Johnston Pettigrew during the retreat after the battle. The Union lost Generals John Reynolds, Samuel K. Zook, Stephen H. Weed, and Elon J. Farnsworth, as well as Strong Vincent, who after being mortally wounded was given a deathbed promotion to brigadier general. Additional senior officer casualties included the wounding of Union Generals Dan Sickles (lost a leg), Francis C. Barlow, Daniel Butterfield, and Winfield Scott Hancock. For the Confederacy, Major General John Bell Hood lost the use of his left arm, while Major General Henry Heth received a shot to the head on the first day of battle (though incapacitated for the rest of the battle, he remarkably survived without long-term injuries, credited in part due to his hat stuffed full of paper dispatches). Confederate Generals James L. Kemper and Isaac R. Trimble were severely wounded during Pickett's charge and captured during the Confederate retreat. General James J. Archer, in command of a brigade that most likely was responsible for killing Reynolds, was taken prisoner shortly after Reynolds' death. 

The following tables summarize casualties by corps for the Union and Confederate forces during the three-day battle.

John L. Burns, veteran of the War of 1812, civilian who fought at the Battle of Gettysburg with Union troops, standing with bayoneted musket. Mathew Brady's National Photographic Portrait Galleries, photographer. From the Liljenquist Family Collection of Civil War Photographs, Prints and Photographs Division, Library of Congress
 
Union Corps Casualties (k/w/m)
I Corps 6059 (666/3231/2162)
II Corps 4369 (797/3194/378)
III Corps 4211 (593/3029/589)
V Corps 2187 (365/1611/211)
VI Corps 242 (27/185/30)
XI Corps 3807 (369/1924/1514)
XII Corps 1082 (204/812/66)
Cavalry Corps 852 (91/354/407)
Artillery Reserve 242 (43/187/12)
Confederate Corps Casualties (k/w/m)
First Corps 7665 (1617/4205/1843)
Second Corps 6686 (1301/3629/1756)
Third Corps 8495 (1724/4683/2088)
Cavalry Corps 380 (66/174/140)

Bruce Catton wrote, "The town of Gettysburg looked as if some universal moving day had been interrupted by catastrophe." But there was only one documented civilian death during the battle: Ginnie Wade (also widely known as Jennie), 20 years old, was hit by a stray bullet that passed through her kitchen in town while she was making bread. Another notable civilian casualty was John L. Burns, a 69-year old veteran of the War of 1812 who walked to the front lines on the first day of battle and participated in heavy combat as a volunteer, receiving numerous wounds in the process. Despite his age and injuries, Burns survived the battle and lived until 1872. Nearly 8,000 had been killed outright; these bodies, lying in the hot summer sun, needed to be buried quickly. Over 3,000 horse carcasses were burned in a series of piles south of town; townsfolk became violently ill from the stench. Meanwhile, the town of Gettysburg, with its population of just 2,400, found itself tasked with taking care of 14,000 wounded Union troops and an additional 8,000 Confederate prisoners.

Confederate retreat

Gettysburg Campaign (July 5 – July 14, 1863)

The armies stared at one another in a heavy rain across the bloody fields on July 4, the same day that, some 900 miles (1,500 km) away, the Vicksburg garrison surrendered to Maj. Gen. Ulysses S. Grant. Lee had reformed his lines into a defensive position on Seminary Ridge the night of July 3, evacuating the town of Gettysburg. The Confederates remained on the battlefield, hoping that Meade would attack, but the cautious Union commander decided against the risk, a decision for which he would later be criticized. Both armies began to collect their remaining wounded and bury some of the dead. A proposal by Lee for a prisoner exchange was rejected by Meade.

Lee started his Army of Northern Virginia in motion late the evening of July 4 towards Fairfield and Chambersburg. Cavalry under Brig. Gen. John D. Imboden was entrusted to escort the miles-long wagon train of supplies and wounded men that Lee wanted to take back to Virginia with him, using the route through Cashtown and Hagerstown to Williamsport, Maryland. Meade's army followed, although the pursuit was half-spirited. The recently rain-swollen Potomac trapped Lee's army on the north bank of the river for a time, but when the Union troops finally caught up, the Confederates had forded the river. The rear-guard action at Falling Waters on July 14 added some more names to the long casualty lists, including General Pettigrew, who was mortally wounded. General James L. Kemper, severely wounded during Pickett's charge, was captured during Lee's retreat.

In a brief letter to Maj. Gen. Henry W. Halleck written on July 7, Lincoln remarked on the two major Union victories at Gettysburg and Vicksburg. He continued:
Now, if Gen. Meade can complete his work so gloriously prosecuted thus far, by the literal or substantial destruction of Lee's army, the rebellion will be over.
Halleck then relayed the contents of Lincoln's letter to Meade in a telegram. However, the Army of the Potomac was exhausted by days of fighting and heavy losses. Furthermore, Meade was forced to detach 4,000 troops North to suppress the New York City Draft Riots, further reducing the effectiveness of his pursuit. Despite repeated pleas from Lincoln and Halleck, which continued over the next week, Meade did not pursue Lee's army aggressively enough to destroy it before it crossed back over the Potomac River to safety in the South. The campaign continued into Virginia with light engagements until July 23, in the minor Battle of Manassas Gap, after which Meade abandoned any attempts at pursuit and the two armies took up positions across from each other on the Rappahannock River.

Union reaction to the news of the victory

The news of the Union victory electrified the North. A headline in The Philadelphia Inquirer proclaimed "VICTORY! WATERLOO ECLIPSED!" New York diarist George Templeton Strong wrote:
The results of this victory are priceless. ... The charm of Robert E. Lee's invincibility is broken. The Army of the Potomac has at last found a general that can handle it, and has stood nobly up to its terrible work in spite of its long disheartening list of hard-fought failures. ... Copperheads are palsied and dumb for the moment at least. ... Government is strengthened four-fold at home and abroad.
— George Templeton Strong, Diary, p. 330.
However, the Union enthusiasm soon dissipated as the public realized that Lee's army had escaped destruction and the war would continue. Lincoln complained to Secretary of the Navy Gideon Welles that "Our army held the war in the hollow of their hand and they would not close it!" Brig. Gen. Alexander S. Webb wrote to his father on July 17, stating that such Washington politicians as "Chase, Seward and others," disgusted with Meade, "write to me that Lee really won that Battle!"

Effect on the Confederacy

In fact, the Confederates had lost militarily and also politically. During the final hours of the battle, Confederate Vice President Alexander Stephens was approaching the Union lines at Norfolk, Virginia, under a flag of truce. Although his formal instructions from Confederate President Jefferson Davis had limited his powers to negotiate on prisoner exchanges and other procedural matters, historian James M. McPherson speculates that he had informal goals of presenting peace overtures. Davis had hoped that Stephens would reach Washington from the south while Lee's victorious army was marching toward it from the north. President Lincoln, upon hearing of the Gettysburg results, refused Stephens's request to pass through the lines. Furthermore, when the news reached London, any lingering hopes of European recognition of the Confederacy were finally abandoned. Henry Adams, whose father was serving as the U.S ambassador to the United Kingdom at the time, wrote, "The disasters of the rebels are unredeemed by even any hope of success. It is now conceded that all idea of intervention is at an end."

Compounding the effects of the defeat would be the end of the Siege of Vicksburg, which surrendered to Grant's Federal armies in the West on July 4, the day after the Gettysburg battle.

The immediate reaction of the Southern military and public sectors was that Gettysburg was a setback, not a disaster. The sentiment was that Lee had been successful on July 1 and had fought a valiant battle on July 2–3, but could not dislodge the Union Army from the strong defensive position to which it fled. The Confederates successfully stood their ground on July 4 and withdrew only after they realized Meade would not attack them. The withdrawal to the Potomac that could have been a disaster was handled masterfully. Furthermore, the Army of the Potomac had been kept away from Virginia farmlands for the summer and all predicted that Meade would be too timid to threaten them for the rest of the year. Lee himself had a positive view of the campaign, writing to his wife that the army had returned "rather sooner than I had originally contemplated, but having accomplished what I proposed on leaving the Rappahannock, viz., relieving the Valley of the presence of the enemy and drawing his Army north of the Potomac." He was quoted as saying to Maj. John Seddon, brother of the Confederate secretary of war, "Sir, we did whip them at Gettysburg, and it will be seen for the next six months that that army will be as quiet as a sucking dove." Some Southern publications, such as the Charleston Mercury, were critical of Lee's actions. On August 8, Lee offered his resignation to President Davis, who quickly rejected it.

Gettysburg became a postbellum focus of the "Lost Cause", a movement by writers such as Edward A. Pollard and Jubal Early to explain the reasons for the Confederate defeat in the war. A fundamental premise of their argument was that the South was doomed because of the overwhelming advantage in manpower and industrial might possessed by the North. They also contend that Robert E. Lee, who up until this time had been almost invincible, was betrayed by the failures of some of his key subordinates at Gettysburg: Ewell, for failing to seize Cemetery Hill on July 1; Stuart, for depriving the army of cavalry intelligence for a key part of the campaign; and especially Longstreet, for failing to attack on July 2 as early and as forcefully as Lee had originally intended. In this view, Gettysburg was seen as a great lost opportunity, in which a decisive victory by Lee could have meant the end of the war in the Confederacy's favor.

After the war, General Pickett was asked why Confederates lost at Gettysburg. He was reported to have said, "I always thought the Yankees had something to do with it."

Gettysburg Address

Gettysburg, November 19, 1863. Crowd of citizens, soldiers, and etc., with a red arrow indicating Abraham Lincoln
 

The ravages of war were still evident in Gettysburg more than four months later when, on November 19, the Soldiers' National Cemetery was dedicated. During this ceremony, President Abraham Lincoln honored the fallen and redefined the purpose of the war in his historic Gettysburg Address.

Medal of Honor

There were 72 Medals of Honor awarded for the Gettysburg Campaign. 64 of the awards were for actions taken during the battle itself, with the first recipient being awarded in December 1864. The last Medal of Honor was posthumously awarded to Lieutenant Alonzo Cushing in 2014.

Historical assessment

Decisive victory controversies

The nature of the result of the Battle of Gettysburg has been the subject of controversy. Although not seen as overwhelmingly significant at the time, particularly since the war continued for almost two years, in retrospect it has often been cited as the "turning point", usually in combination with the fall of Vicksburg the following day. This is based on the observation that, after Gettysburg, Lee's army conducted no more strategic offensives—his army merely reacted to the initiative of Ulysses S. Grant in 1864 and 1865—and by the speculative viewpoint of the Lost Cause writers that a Confederate victory at Gettysburg might have resulted in the end of the war.

[The Army of the Potomac] had won a victory. It might be less of a victory than Mr. Lincoln had hoped for, but it was nevertheless a victory—and, because of that, it was no longer possible for the Confederacy to win the war. The North might still lose it, to be sure, if the soldiers or the people should lose heart, but outright defeat was no longer in the cards.
Bruce Catton, Glory Road
 
It is currently a widely held view that Gettysburg was a decisive victory for the Union, but the term is considered imprecise. It is inarguable that Lee's offensive on July 3 was turned back decisively and his campaign in Pennsylvania was terminated prematurely (although the Confederates at the time argued that this was a temporary setback and that the goals of the campaign were largely met). However, when the more common definition of "decisive victory" is intended—an indisputable military victory of a battle that determines or significantly influences the ultimate result of a conflict—historians are divided. For example, David J. Eicher called Gettysburg a "strategic loss for the Confederacy" and James M. McPherson wrote that "Lee and his men would go on to earn further laurels. But they never again possessed the power and reputation they carried into Pennsylvania those palmy summer days of 1863."

However, Herman Hattaway and Archer Jones wrote that the "strategic impact of the Battle of Gettysburg was ... fairly limited." Steven E. Woodworth wrote that "Gettysburg proved only the near impossibility of decisive action in the Eastern theater." Edwin Coddington pointed out the heavy toll on the Army of the Potomac and that "after the battle Meade no longer possessed a truly effective instrument for the accomplishments of his task. The army needed a thorough reorganization with new commanders and fresh troops, but these changes were not made until Grant appeared on the scene in March 1864." Joseph T. Glatthaar wrote that "Lost opportunities and near successes plagued the Army of Northern Virginia during its Northern invasion," yet after Gettysburg, "without the distractions of duty as an invading force, without the breakdown of discipline, the Army of Northern Virginia [remained] an extremely formidable force." Ed Bearss wrote, "Lee's invasion of the North had been a costly failure. Nevertheless, at best the Army of the Potomac had simply preserved the strategic stalemate in the Eastern Theater ..." Furthermore, the Confederacy soon proved it was still capable of winning significant victories over the Northern forces in both the East (Battle of Cold Harbor) and West (Battle of Chickamauga).

Peter Carmichael refers to the military context for the armies, the "horrendous losses at Chancellorsville and Gettysburg, which effectively destroyed Lee's offensive capacity," implying that these cumulative losses were not the result of a single battle. Thomas Goss, writing in the U.S. Army's Military Review journal on the definition of "decisive" and the application of that description to Gettysburg, concludes: "For all that was decided and accomplished, the Battle of Gettysburg fails to earn the label 'decisive battle'." The military historian John Keegan agrees. Gettysburg was a landmark battle, the largest of the war and it would not be surpassed. The Union had restored to it the belief in certain victory, and the loss dispirited the Confederacy. If "not exactly a decisive battle", Gettysburg was the end of Confederate use of Northern Virginia as a military buffer zone, the setting for Grant's Overland Campaign.

Lee vs. Meade

Photo of a balding and bearded George Meade in a military uniform. The somewhat thin figure is standing while holding a kepi.
George G. Meade

Prior to Gettysburg, Robert E. Lee had established a reputation as an almost invincible general, achieving stunning victories against superior numbers—although usually at the cost of high casualties to his army—during the Seven Days, the Northern Virginia Campaign (including the Second Battle of Bull Run), Fredericksburg, and Chancellorsville. Only the Maryland Campaign, with its tactically inconclusive Battle of Antietam, had been less than successful. Therefore, historians have attempted to explain how Lee's winning streak was interrupted so dramatically at Gettysburg. Although the issue is tainted by attempts to portray history and Lee's reputation in a manner supporting different partisan goals, the major factors in Lee's loss arguably can be attributed to: (1) his overconfidence in the invincibility of his men; (2) the performance of his subordinates, and his management thereof; (3) his failing health, and (4) the performance of his opponent, George G. Meade, and the Army of the Potomac.

Photo of white-haired and bearded Robert E. Lee in a double breasted gray uniform with three stars on his collar
Robert E. Lee

Throughout the campaign, Lee was influenced by the belief that his men were invincible; most of Lee's experiences with the Army of Northern Virginia had convinced him of this, including the great victory at Chancellorsville in early May and the rout of the Union troops at Gettysburg on July 1. Since morale plays an important role in military victory when other factors are equal, Lee did not want to dampen his army's desire to fight and resisted suggestions, principally by Longstreet, to withdraw from the recently captured Gettysburg to select a ground more favorable to his army. War correspondent Peter W. Alexander wrote that Lee "acted, probably, under the impression that his troops were able to carry any position however formidable. If such was the case, he committed an error, such however as the ablest commanders will sometimes fall into." Lee himself concurred with this judgment, writing to President Davis, "No blame can be attached to the army for its failure to accomplish what was projected by me, nor should it be censured for the unreasonable expectations of the public—I am alone to blame, in perhaps expecting too much of its prowess and valor."

The most controversial assessments of the battle involve the performance of Lee's subordinates. The dominant theme of the Lost Cause writers and many other historians is that Lee's senior generals failed him in crucial ways, directly causing the loss of the battle; the alternative viewpoint is that Lee did not manage his subordinates adequately, and did not thereby compensate for their shortcomings. Two of his corps commanders—Richard S. Ewell and A.P. Hill—had only recently been promoted and were not fully accustomed to Lee's style of command, in which he provided only general objectives and guidance to their former commander, Stonewall Jackson; Jackson translated these into detailed, specific orders to his division commanders. All four of Lee's principal commanders received criticism during the campaign and battle:
  • James Longstreet suffered most severely from the wrath of the Lost Cause authors, not the least because he directly criticized Lee in postbellum writings and became a Republican after the war. His critics accuse him of attacking much later than Lee intended on July 2, squandering a chance to hit the Union Army before its defensive positions had firmed up. They also question his lack of motivation to attack strongly on July 2 and 3 because he had argued that the army should have maneuvered to a place where it would force Meade to attack them. The alternative view is that Lee was in close contact with Longstreet during the battle, agreed to delays on the morning of July 2, and never criticized Longstreet's performance. (There is also considerable speculation about what an attack might have looked like before Dan Sickles moved the III Corps toward the Peach Orchard.)
  • J.E.B. Stuart deprived Lee of cavalry intelligence during a good part of the campaign by taking his three best brigades on a path away from the army's. This arguably led to Lee's surprise at Hooker's vigorous pursuit; the engagement on July 1 that escalated into the full battle prematurely; and it also prevented Lee from understanding the full disposition of the enemy on July 2. The disagreements regarding Stuart's culpability for the situation originate in the relatively vague orders issued by Lee, but most modern historians agree that both generals were responsible to some extent for the failure of the cavalry's mission early in the campaign.
  • Richard S. Ewell has been universally criticized for failing to seize the high ground on the afternoon of July 1. Once again the disagreement centers on Lee's orders, which provided general guidance for Ewell to act "if practicable." Many historians speculate that Stonewall Jackson, if he had survived Chancellorsville, would have aggressively seized Culp's Hill, rendering Cemetery Hill indefensible, and changing the entire complexion of the battle. A differently worded order from Lee might have made the difference with this subordinate.
  • A.P. Hill has received some criticism for his ineffective performance. His actions caused the battle to begin and then escalate on July 1, despite Lee's orders not to bring on a general engagement (although historians point out that Hill kept Lee well informed of his actions during the day). However, Hill's illness minimized his personal involvement in the remainder of the battle, and Lee took the explicit step of temporarily removing troops from Hill's corps and giving them to Longstreet for Pickett's Charge.
Photo of dark-haired and bearded Winfield S. Hancock in a dark uniform with a determined look
Winfield S. Hancock

In addition to Hill's illness, Lee's performance was affected by heart troubles, which would eventually lead to his death in 1870; he had been diagnosed with pericarditis by his staff physicians in March 1863, though modern doctors believe he had in fact suffered a heart attack. He wrote to Jefferson Davis that his physical condition prevented him from offering full supervision in the field, and said, "I am so dull that in making use of the eyes of others I am frequently misled."

As a final factor, Lee faced a new and formidable opponent in George G. Meade, and the Army of the Potomac fought well on its home territory. Although new to his army command, Meade deployed his forces relatively effectively; relied on strong subordinates such as Winfield S. Hancock to make decisions where and when they were needed; took great advantage of defensive positions; nimbly shifted defensive resources on interior lines to parry strong threats; and, unlike some of his predecessors, stood his ground throughout the battle in the face of fierce Confederate attacks.

Lee was quoted before the battle as saying Meade "would commit no blunders on my front and if I make one ... will make haste to take advantage of it." That prediction proved to be correct at Gettysburg. Stephen Sears wrote, "The fact of the matter is that George G. Meade, unexpectedly and against all odds, thoroughly outgeneraled Robert E. Lee at Gettysburg." Edwin B. Coddington wrote that the soldiers of the Army of the Potomac received a "sense of triumph which grew into an imperishable faith in [themselves]. The men knew what they could do under an extremely competent general; one of lesser ability and courage could well have lost the battle."

Meade had his own detractors as well. Similar to the situation with Lee, Meade suffered partisan attacks about his performance at Gettysburg, but he had the misfortune of experiencing them in person. Supporters of his predecessor, Maj. Gen. Joseph Hooker, lambasted Meade before the U.S. Congress's Joint Committee on the Conduct of the War, where Radical Republicans suspected that Meade was a Copperhead and tried in vain to relieve him from command. Daniel E. Sickles and Daniel Butterfield accused Meade of planning to retreat from Gettysburg during the battle. Most politicians, including Lincoln, criticized Meade for what they considered to be his half-hearted pursuit of Lee after the battle. A number of Meade's most competent subordinates—Winfield S. Hancock, John Gibbon, Gouverneur K. Warren, and Henry J. Hunt, all heroes of the battle—defended Meade in print, but Meade was embittered by the overall experience.

Battlefield preservation

CW Arty M1857 Napoleon front.jpg
M1857 12-Pounder "Napoleon" at Gettysburg National Military Park Gettysburg, Pennsylvania.
LocationAdams, Pennsylvania, United States
WebsitePark Home (NPS.gov)

Today, the Gettysburg National Cemetery and Gettysburg National Military Park are maintained by the U.S. National Park Service as two of the nation's most revered historical landmarks. Although Gettysburg is one of the best known of all Civil War battlefields, it too faces threats to its preservation and interpretation. Many historically significant locations on the battlefield lie outside the boundaries of Gettysburg National Military Park and are vulnerable to residential or commercial development. 

On July 20, 2009, a Comfort Inn and Suites opened on Cemetery Hill, adjacent to Evergreen Cemetery, just one of many modern edifices infringing on the historic field. The Baltimore Pike corridor attracts development that concerns preservationists.

Some preservation successes have emerged in recent years. Two proposals to open a casino at Gettysburg were defeated in 2006 and most recently in 2011, when public pressure forced the Pennsylvania Gaming Control Board to reject the proposed gambling hub at the intersection of Routes 15 and 30, near East Cavalry Field. The Civil War Trust also successfully purchased and transferred 95 acres at the former site of the Gettysburg Country Club to the control of the U.S. Department of the Interior in 2011.

Less than half of the over 11,500 acres on the old Gettysburg Battlefield have been preserved for posterity thus far. The Civil War Trust (a division of the American Battlefield Trust) and its partners have acquired and preserved 1,022 acres (4.14 km2) of the battlefield in more than 30 separate transactions since 1997. Some of these acres are now among the 4,998 acres of the Gettysburg National Military Park. In 2015, the Trust made one of its most important and expensive acquisitions, paying $6 million for a four-acre parcel that included the stone house that Confederate Gen. Robert E. Lee used as his headquarters during the battle. The Trust razed a motel, restaurant and other buildings within the parcel to restore Lee's Headquarters and the site to their wartime appearance, adding interpretive signs. It opened the site to the public in October, 2016.

Commemoration in U.S. postage and coinage

Gettysburg Centennial Commemorative issue of 1963
 
Gettysburg National Military Park Quarter, issued 2011

During the Civil War Centennial, the U.S. Post Office issued five postage stamps commemorating the 100th anniversaries of famous battles, as they occurred over a four-year period, beginning with the Battle of Fort Sumter Centennial issue of 1961. The Battle of Shiloh commemorative stamp was issued in 1962, the Battle of Gettysburg in 1963, the Battle of the Wilderness in 1964, and the Appomattox Centennial commemorative stamp in 1965. A commemorative half dollar for the battle was produced in 1936. As was typical for the period, mintage for the coin was very low, just 26,928. On January 24, 2011, the America the Beautiful quarters released a 25-cent coin commemorating Gettysburg National Military Park and the Battle of Gettysburg. The reverse side of the coin depicts the monument on Cemetery Ridge to the 72nd Pennsylvania Infantry.

In popular culture

Film records survive of two Gettysburg reunions, held on the battlefield. At the 50th anniversary (1913), veterans re-enacted Pickett's Charge in a spirit of reconciliation, a meeting that carried great emotional force for both sides. At the 75th anniversary (1938), 2500 veterans attended, and there was a ceremonial mass hand-shake across a stone wall. This was recorded on sound film, and some Confederates can be heard giving the Rebel Yell.

The Battle of Gettysburg was depicted in the 1993 film Gettysburg, based on Michael Shaara's 1974 novel The Killer Angels. The film and novel focused primarily on the actions of Joshua Lawrence Chamberlain, John Buford, Robert E. Lee, and James Longstreet during the battle. The first day focused on Buford's cavalry defense, the second day on Chamberlain's defense at Little Round Top, and the third day on Pickett's Charge

The south winning the Battle of Gettysburg is a popular premise for a point of divergence in American Civil War alternate histories. Here are some examples which either depict or make significant reference to an alternate Battle of Gettysburg (sometimes simply inserting fantasy or sci-fi elements in an account of the battle):

Saturday, June 27, 2020

Brain asymmetry

From Wikipedia, the free encyclopedia
In human neuroanatomy, brain asymmetry can refer to at least two quite distinct findings:
A stereotypical image of brain lateralisation - demonstrated to be false in neuroscientific research.
Neuroanatomical differences themselves exist on different scales, from neuronal densities, to the size of regions such as the planum temporale, to—at the largest scale—the torsion or "wind" in the human brain, reflected shape of the skull, which reflects a backward (posterior) protrusion of the left occipital bone and a forward (anterior) protrusion of the right frontal bone. In addition to gross size differences, both neurochemical and structural differences have been found between the hemispheres. Asymmetries appear in the spacing of cortical columns, as well as dendritic structure and complexity. Larger cell sizes are also found in layer III of Broca's area.

The human brain has an overall leftward posterior and rightward anterior asymmetry (or brain torque). There are particularly large asymmetries in the frontal, temporal and occipital lobes, which increase in asymmetry in the antero-posterior direction beginning at the central region. Leftward asymmetry can be seen in the Heschl gyrus, parietal operculum, Silvian fissure, left cingulate gyrus, temporo-parietal region and planum temporale. Rightward asymmetry can be seen in the right central sulcus (potentially suggesting increased connectivity between motor and somatosensory cortices in the left side of the brain), lateral ventricle, entorhinal cortex, amygdala and temporo-parieto-occipital area. Sex-dependent brain asymmetries are also common. For example, human male brains are more asymmetrically lateralized than those of females. However, gene expression studies done by Hawrylycz and colleagues and Pletikos and colleagues, were not able to detect asymmetry between the hemispheres on the population level.

History

In the mid-19th century scientists first began to make discoveries regarding lateralization of the brain, or differences in anatomy and corresponding function between the brain's two hemispheres. Franz Gall, a German anatomist, was the first to describe what is now known as the Doctrine of Cerebral Localization. Gall believed that, rather than the brain operating as a single, whole entity, different mental functions could be attributed to different parts of the brain. He was also the first to suggest language processing happened in the frontal lobes. However, Gall's theories were controversial among many scientists at the time. Others were convinced by experiments such as those conducted by Marie-Jean-Pierre Flourens, in which he demonstrated lesions to bird brains caused irreparable damage to vital functions. Flourens's methods, however, were not precise; the crude methodology employed in his experiments actually caused damage to several areas of the tiny brains of the avian models. 

Paul Broca was among the first to offer compelling evidence for localization of function when he identified an area of the brain related to speech.
In 1861 surgeon Paul Broca provided evidence that supported Gall's theories. Broca discovered that two of his patients who had suffered from speech loss had similar lesions in the same area of the left frontal lobe. While this was compelling evidence for localization of function, the connection to “sidedness” was not made immediately. As Broca continued to study similar patients, he made the connection that all of the cases involved damage to the left hemisphere, and in 1864 noted the significance of these findings—that this must be a specialized region. He also—incorrectly—proposed theories about the relationship of speech areas to “handedness”.

Accordingly, some of the most famous early studies on brain asymmetry involved speech processing. Asymmetry in the Sylvian fissure (also known as the lateral sulcus), which separates the frontal and parietal lobes from the temporal lobe, was one of the first incongruencies to be discovered. Its anatomical variances are related to the size and location of two areas of the human brain that are important for language processing, Broca's area and Wernicke's area, both in the left hemisphere.

Around the same time that Broca and Wernicke made their discoveries, neurologist Hughlings Jackson suggested the idea of a “leading hemisphere”—or, one side of the brain that played a more significant role in overall function—which would eventually pave the way for understanding hemispheric “dominance” for various processes. Several years later, in the mid-20th century, critical understanding of hemispheric lateralization for visuospatial, attention and perception, auditory, linguistic and emotional processing came from patients who underwent split-brain procedures to treat disorders such as epilepsy. In split-brain patients, the corpus callosum is cut, severing the main structure for communication between the two hemispheres. The first modern split-brain patient was a war veteran known as Patient W.J., whose case contributed to further understanding of asymmetry.

Brain asymmetry is not unique to humans. In addition to studies on human patients with various diseases of the brain, much of what is understood today about asymmetries and lateralization of function has been learned through both invertebrate and vertebrate animal models, including zebrafish, pigeons, rats, and many others. For example, more recent studies revealing sexual dimorphism in brain asymmetries in the cerebral cortex and hypothalamus of rats show that sex differences emerging from hormonal signaling can be an important influence on brain structure and function. Work with zebrafish has been especially informative because this species provides the best model for directly linking asymmetric gene expression with asymmetric morphology, and for behavioral analyses.

Brain Asymmetry in Humans

Lateralized Functional Differences and Significant regions in each side of the brain and their function

The left and right hemispheres operate the contralateral sides of the body. Each hemisphere contains sections of all 4 lobes: the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. The two hemispheres are separated along the mediated longitudinal fissure and are connected by the corpus callosum which allows for communication and coordination of stimuli and information. The corpus callosum is the largest collective pathway of white matter tissue in the body that is made of more than 200 million nerve fibers. The left and right hemispheres are associated with different functions and specialize in interpreting the same data in different ways, referred to as lateralization of the brain. The left hemisphere is associated with language and calculations, while the right hemisphere is more closely associated with visual-spatial recognition and facial recognition. This lateralization of brain function results in some specialized regions being only present in a certain hemisphere or being dominant in one hemisphere versus the other. Some of the significant regions included in each hemisphere are listed below.

Left Hemisphere

Broca's area is located in the left hemisphere prefrontal cortex above the cingulate gyrus in the third frontal convolution. Broca's area was discovered by Paul Broca in 1865. This area handles speech production. Damage to this area would result in Broca aphasia which causes the patient to become unable to formulate coherent appropriate sentences.

Wernicke's area was discovered in 1976 by Carl Wernicke and was found to be the site of language comprehension. Wernicke's area is also found in the left hemisphere in the temporal lobe. Damage to this area of the brain results in the individual losing the ability to understand language. However, they are still able to produce sounds, words, and sentence although they are not used in the appropriate context.

Right Hemisphere

The Fusiform Face Area (FFA) is an area that has been studied to be highly active when faces are being attended to in the visual field. A FFA is found to be present in both hemispheres, however, studies have found that the FFA is predominantly lateralized in the right hemisphere where a more in-depth cognitive processing of faces is conducted. The left hemisphere FFA is associated with rapid processing of faces and their features.

Other Regions and Associated Diseases

Some significant regions that can present as asymmetrical in the brain can result in either of the hemispheres due to factors such as genetics. An example would include handedness. Handedness can result from asymmetry in the motor cortex of one hemisphere. For right handed individuals, since the brain operates the contralateral side of the body, they could have a more induced motor cortex in the left hemisphere.

Several diseases have been found to exacerbate brain asymmetries that are already present in the brain. Researchers are starting to look into the effect and relationship of brain asymmetries to diseases such as schizophrenia and dyslexia.





Schizophrenia is a complex long-term mental disorder that causes hallucinations, delusions and a lack of concentration, thinking, and motivation in an individual. Studies have found that individuals with schizophrenia have a lack in brain asymmetry thus reducing the functional efficiency of affected regions such as the frontal lobe. Conditions include leftward functional hemispheric lateralization, loss of laterality for language comprehension, a reduction in gyrification, brain torsion etc.

As study earlier, language is usually dominant in the left hemisphere. Developmental language disorders, such as dyslexia, have been researched using brain imaging techniques to understand the neuronal or structural changes associated with the disorder. Past research has exhibited that hemispheric asymmetries that are usually found in healthy adults such as the size of the temporal lobe is not present in adult patients with dyslexia. In conjunction, past research has exhibited that patients with dyslexia lack a lateralization of language in their brain compared to healthy patients. Instead patients with dyslexia showed to have a bilateral hemispheric dominance for language.

Current Research on Brain Asymmetry


Lateralization of function and asymmetry in the human brain continues to propel a popular branch of neuroscientific and psychological inquiry. Technological advancements for brain mapping have enabled researchers to see more parts of the brain more clearly, which has illuminated previously undetected lateralization differences that occur during different life stages. As more information emerges, researchers are finding insights into how and why early human brains may have evolved the way that they did to adapt to social, environmental and pathological changes. This information provides clues regarding plasticity, or how different parts of the brain can sometimes be recruited for different functions.

Continued study of brain asymmetry also contributes to the understanding and treatment of complex diseases. Neuroimaging in patients with Alzheimer's disease, for example, shows significant deterioration in the left hemisphere, along with a rightward hemispheric dominance—which could relate to recruitment of resources to that side of the brain in the face of damage to the left. These hemispheric changes have been connected to performance on memory tasks.

As has been the case in the past, studies on language processing and the implications of left- and right- handedness also dominate current research on brain asymmetry.

Dual consciousness

From Wikipedia, the free encyclopedia
 
Dual consciousness is a theoretical concept in neuroscience. It is proposed that it is possible that a person may develop two separate conscious entities within their one brain after undergoing a corpus callosotomy. The idea first began circulating in the neuroscience community after some split-brain patients exhibited the alien hand syndrome, which led some scientists to believe that there must be two separate consciousnesses within the brain's left and right hemispheres in competition with one another once the corpus callosum is severed.

The idea of dual consciousness has caused controversy in the neuroscience community. It has not been conclusively proven or disproven.

Background

During the first half of the 20th Century, some neurosurgeons concluded that the best option of treating severe epilepsy was by severing the patient's corpus callosum. The corpus callosum is the primary communication mechanism between the brain's two cerebral hemispheres. For example, communication across the callosum allows information from both the left and right visual fields to be interpreted by the brain in a way that makes sense to comprehend the person's actual experience (visual inputs from both eyes are interpreted by the brain to make sense of the experience that you are looking at a computer that is directly in front of you). The procedure of surgically removing the corpus callosum is called a corpus callosotomy. Patients who have undergone a corpus callosotomy are colloquially referred to as "split-brain patients". They are called so because now their brain's left and right hemispheres are no longer connected by the corpus callosum.

Split-brain patients have been subjects for numerous psychological experiments that sought to discover what occurs in the brain now that the primary interhemispheric pathways have been disrupted. Notable researchers in the field include Roger Sperry, one of the first to publish ideas involving a dual consciousness, and his famous graduate student, Michael Gazzaniga. Their results found a pattern among patients: severing the entire corpus callosum stops the interhemispheric transfer of perceptual, sensory, motor, and other forms of information. For most cases, corpus callosotomies did not in any way affect patients' real world functioning, however, those psychology experiments have demonstrated some interesting differences between split-brain patients and normal subjects.

Split-brain patients and the corpus callosotomy

The first successful corpus callosotomies on humans were performed in the 1930s. The purpose of the procedure was to alleviate the effects of epilepsy when other forms of treatment (medications) had failed to stop the violent convulsions associated with the disorder. Epileptic seizures occur because of abnormal electrical discharges that spread across areas of the brain. William Van Wagenen proposed the idea of severing the corpus callosum to eliminate transcortical electrical signals across the brain's hemispheres. If this could be achieved, then the seizures should be reduced or even completely eliminated. 

The general procedure of a corpus callosotomy is as follows. The patient is put under anesthesia. Once the patient is in deep sleep, a craniotomy is performed. This procedure removes a section of the skull, leaving the brain exposed and accessible to the surgeon. The dura mater is pulled back so the deeper areas of the brain, including the corpus callosum, can be seen. Specialized instruments are placed into the brain that allows safe severing of the corpus. Initially, a partial callosotomy is performed, which only severs the front two thirds of the callosum. It is important to note that because the back section of the callosum is preserved, visual information is still sent across both hemispheres. Though the corpus callosum loses a majority of its functioning during a partial callosotomy, it does not completely lose its capabilities. If this operation does not succeed in reducing the seizures, a complete callosotomy is needed to reduce the severity of the seizures.

A similar type of procedure, known as a, involves severing a number of interhemispheric tracts (such as the anterior commissure, the hippocampal commissure and the massa intermedia of the thalamus) in addition to the corpus callosum.

After surgery, the split-brain patients are often given extensive neuropsychological assessments. An interesting finding among split-brain patients is many of them claim to feel normal after the surgery and do not feel that their brains are "split". The corpus callosotomy and commissurotomy have been successful in reducing, and in some cases, completely eliminating epileptic seizures. Van Wagenen's theory was correct.

Alien hand syndrome

Alien hand syndrome, sometimes used synonymously with anarchic hand is a neurological disorder in which the afflicted person's hand appears to take on a mind of its own. Alien hand syndrome has been documented in some split brain patients.

Symptoms

The classic sign of Alien Hand Syndrome is that the affected person cannot control one of their hands. For example, if a split-brain patient with Alien Hand Syndrome is asked to pick up a glass with their right hand, as the right hand moves over to the glass, the left hand will interfere with the action, thwarting the right hand's task. The interference from the left hand is completely out of the control of the patient and is not being done “on purpose”. Affected patients at times cannot control the movements of their hands. Another example included patients unbuttoning a shirt with one hand, and the other hand simultaneously re-buttoning the shirt (although some reported feeling normal after their surgery).

Relationship to dual consciousness

When scientists first started observing the alien hand syndrome in split-brain patients, they began to question the nature of consciousness and began to theorize that perhaps when the corpus callosum is cut, consciousness also is split into two separate entities. This development added to the general appeal of split-brain research.

Gazzaniga and LeDoux's experiment

Procedure and results

In 1978, Michael Gazzaniga and Joseph DeLoux discovered a unique phenomenon among split-brain patients who were asked to perform a simultaneous concept task. The patient was shown 2 pictures: of a house in the winter time and of a chicken's claw. The pictures were positioned so they would exclusively be seen in only one visual field of the brain (the winter house was positioned so it would only be seen in the patient's left visual field (LVF), which corresponds to the brain's right hemisphere, and the chicken's claw was placed so it would only be seen in the patient's right visual field (RVF), which corresponds to the brain's left hemisphere).

A series of pictures was placed in front of the patients. Gazzaniga and LeDoux then asked the patient to choose a picture with his right hand and a picture with his left hand. The paradigm was set up so the choices would be obvious for the patients. A snow shovel is used for shoveling the snowy driveway of the winter house and a chicken's head correlates to the chicken's claw. The other pictures do not in any way correlate with the 2 original pictures. In the study, a patient chose the snow shovel with his left hand (corresponding to his brain's right hemisphere) and his right hand chose the chicken's head (corresponding to the brain's left hemisphere). When the patient was asked why he had chosen the pictures he had chosen, the answer he gave was “The chicken claw goes with the chicken head, and you need a snow shovel to clean out the chicken shed”.

Why would he say this? Wouldn't it be obvious that the shovel goes with the winter house? For people with an intact corpus callosum, yes it is obvious, but not for a split-brain patient. Both the winter house and the shovel are being projected to the patient from his LVF, so his right hemisphere is receiving and processing the information and this input is completely independent from what is going on in the RVF, which involves the chicken's claw and head (the information being processed in the left hemisphere). The human brain's left hemisphere is primarily responsible interpreting the meaning of the sensory input it receives from both fields, however the left hemisphere has no knowledge of the winter house. Because it has no knowledge of the winter house, it must invent a logical reason for why the shovel was chosen. Since the only objects it has to work with are the chicken's claw and head, the left hemisphere interprets the meaning of choosing the shovel as “it is an object necessary to help the chicken, which lives in a shed, therefore, the shovel is used to clean the chicken’s shed”. Gazzaniga famously coined the term left brain interpreter to explain this phenomenon.

Interpreting Gazzaniga's "left brain interpreter"

What does the results of Gazzaniga and LeDoux's work suggest about the existence of a dual consciousness? There are varying possibilities.
  • The left hemisphere dominates all interpretation of the split-brain patient's perceptual field, with the right hemisphere having little importance in these processes.
  • If so, one could by extension claim there are 2 separate conscious entities that do not interact with each other or are in competition with each other and have separate interpretations of the stimuli, the left hemisphere winning the struggle.
  • Or perhaps the right hemisphere is unconscious of the snow house and shovel while the left hemisphere retains a conscious perception of its objects.

Other experiments

Sperry–Gazzaniga

The Gazzaniga–LeDoux studies were based on previous studies done by Sperry and Gazzaniga. Sperry examined split-brain patients. Sperry's experiment included a subject being seated at a table, with a shield blocking the visions from the subject's hands, including the objects on the table and the examiner seated across. The shield was also used as a viewing screen. On the shield, the examiner can select to present the visual material to both hemispheres or to selective hemispheres by means of having the patient look at certain points on the viewing screen. The patient is briefly exposed to the stimuli on the viewing screen. The stimuli shown to the left eye goes to the right hemisphere and the visual material shown to the right eye will be projected to the left hemisphere. During the experiment, when the stimulus was shown to the left side of the screen, the patient indicated he did not see anything. Patients have shown the inability to describe in writing or in speech the stimuli that was shown briefly to the left side. The speaking hemisphere, which in most people is the left hemisphere, would not have awareness of stimulus being shown to the right hemisphere (left visual field), except the left hand was able to point to the correct object. Based off his observations and data, Sperry concluded each hemisphere possessed its own consciousness.

Revonsuo

Revonsuo explains a procedure that was similar in nature to the Sperry–Gazzaniga design. Split-brain patients are shown a picture with two objects: a flower and a rabbit. The flower is exclusively shown in the right visual field, which is interpreted by the left hemisphere and the rabbit is exclusively shown in the left visual field, which is interpreted by the right hemisphere. The left brain is seeing the flower as the right brain is simultaneously viewing the rabbit. When the patients were asked what they saw, patients said they only saw the flower and did not see the rabbit. The flower is in the right visual field and the left hemisphere can only see the flower. The left hemisphere dominates the interpretation of the stimulus and since it cannot see the rabbit (only being represented in the right hemisphere), patients do not believe they saw a rabbit. They can, however, still point to the rabbit with their left hand. Revonsuo stated that it seemed that one consciousness saw the flower and another consciousness saw the rabbit independently from one another.

Joseph

Rhawn Joseph observed two patients who had both undergone a complete corpus callosotomy. Joseph observed that one of the patient's right hemisphere is able to gather, comprehend, and express information. The right hemisphere was able to direct activity to the patient's left arm and leg. The execution of the left arm and leg's action as was inhibited by the left hemisphere. Joseph found that the patient's left leg would attempt to move forward as if to walk straight but the right leg would either refuse move or begin to walk in the opposite direction. After observing the struggles of the execution of activities involving the left and right arms and legs, led Joseph to believe that the two hemispheres possessed their own consciousness.

Joseph also noted that the patient had other specific instances of conflict between the right and left hemispheres including, the left hand (right hemisphere) carrying out actions contrary to the left hemisphere's motives such as the left hand turning off the television immediately after the right hand turned it on. Joseph found that the patient's left leg would only allow the patient to return home when the patient was going for a walk and would reject continuing to go for that walk.

Further observations by Joseph

In the laboratory, a patient was given two different fabrics: a wire screen in his left hand and a piece of sandpaper in his right hand. The patient received two different fabrics out of his view so that neither eye nor hemisphere visually seen what his hands were given. When the patient was indicating what fabric was in the left hand, he was able to correctly indicate and point with the left hand to the wire screen after it had been set on a table. As he pointed with his left hand, however, the right hand tried to stop the left hand and make the left hand point to the fabric that the right hand was holding. The left hand continued to point at the correct fabric, even though the right hand tried to forcefully move the left hand. During the struggle, the patient also verbalized feelings of animosity by saying, “That’s wrong!” and “I hate this hand.” Joseph concluded that the left hemisphere did not understand at all why the left hand (right hemisphere) would point to a different material.

Controversy and alternative explanations

Proponents of the dual consciousness theory have caused a great amount of controversy and debate within the neuroscience community. The magnitude of such a claim: that consciousness can be split into two entities within the one brain are considered by some scientists to be audacious. There is no concrete evidence to validate the theory and the current evidence provided is, at best, anecdotal.

The most powerful claims against the dual consciousness theory are:
  • There is no universally accepted definition of “consciousness”.
  • Split-brain patients are not the only people to exhibit the Alien Hand Syndrome. People with intact brains who have suffered a stroke may also have the Alien Hand Syndrome. It also has been observed in patients with Alzheimer's disease or in patients who have brain tumors.
  • Other existing and established neurological mechanisms can account for an explanation of the same phenomena.
Gonzalo Munevar has proposed an alternative explanation to demonstrate that these strange behaviors are spawned from areas in the brain and not by a dual consciousness. Two cortical areas in particular, the supplementary motor area and the premotor cortex, are crucial in the planning of executing motor tasks to external stimuli presented in the person's perceptual field. For example, a person may pick up a glass of water with his right hand and put it up to his lips for a drink. The person may have picked up the glass with his right hand, but well before this action takes place, the PMC and SMA consider a variety of different possibilities of how this action could be performed. He could have picked it up with his left hand, his mouth, even his foot! He could have done it quickly or slowly. Many possibilities are entertained, but few are actually executed. These actions are sent from the PMC to the Motor Cortex for execution. The rest are inhibited by the SMA and are not performed.

It is also important to understand that the processes of the SMA and PMC are done unconsciously. The SMA and PMC consider the many alternative actions many milliseconds before the chosen action takes place. The person is never consciously aware of these alternative possibilities the brain has juggled with before he picks it up with the right hand; he just does it. The action of picking up the glass with the right hand is also performed unconsciously. It may be preferable to use his right hand because he is right handed and doing so is therefore more comfortable or perhaps the glass is placed on his right side and the possibility that expends the least amount of energy is using the right hand to pick it up.

Another important fact about the PMC is that its activation is bilateral. When it is activated, it is activated in both hemispheres of the brain. Gazzaniga observed and wrote about this phenomenon. When the corpus callosum is severed, many interhemispheric interactions are disrupted. Many areas of the brain become compromised, including the SMA. If the SMA has trouble regulating and inhibiting the actions of the PMC, it is very possible that conflicting sets of actions may be sent to the MC and performed (accounting for both hands reaching for the glass, even if only one hand is intended to grab it). It would make the appearance that there is a dual consciousness competing for dominance over the other for control of the brain, but it is not the case.

The fact that the Alien Hand Syndrome eventually goes away in some split-brain patients is not evidence of one consciousness “defeating” the other and taking complete control of the brain. It is likely that the plasticity of the brain may be the cause for alleviating the disorder. Eventually the split patient's brain may find adaptive routes to compensate for the lost interhemispheric communication, such as alternative pathways involving subcortical structures that perform subcortical interhemispheric inhibition to regain a sense of normalcy between the two hemispheres.

Models of multiple consciousnesses

Michael Gazzaniga, while working on the model of dual consciousness, came to the conclusion that simple dual consciousness (i.e. right-brain/left-brain model of the mind) is a gross oversimplification and the brain is organized into hundreds maybe even thousands of modular-processing systems.

The theory of a division of consciousness was touched upon by Carl Jung in 1935 when he stated, "The so-called unity of consciousness is an illusion... we like to think that we are one but we are not."

Similar models (which also claim that mind is formed from many little agents, i.e. the brain is made up of a constellation of independent or semi-independent agents) were also described by:
  • Marvin Minsky'sSociety of Mind” model claims that mind is built up from the interactions of simple parts called agents, which are themselves mindless.
  • Thomas R. Blakeslee described the brain model which claims that brain is composed of hundreds of independent centers of thought called “modules”.
  • Neurocluster Brain Model describes the brain as a massively parallel computing machine in which huge number of neuroclusters process information independently from each other. The neurocluster which most of the time has the access to actuators (i.e. neurocluster which most of the time acts upon an environment using actuators) is called the main personality. Other neuroclusters which do not have access to actuators or which have only short duration and limited access to actuators are called “autonomous neuroclusters”.
  • Michio Kaku described the brain model using the analogy of large corporation which is controlled by CEO.
  • Robert E. Ornstein claimed that the mind is a squadron of simpletons.
  • Ernest Hilgard described neodissociationist theory which claims that a “hidden observer” is created in the mind while hypnosis is taking place and this “hidden observer” has his own separate consciousness.
  • George Ivanovich Gurdjieff in year 1915 taught his students that man has no single, big I; man is divided into a multiplicity of small I’s.

Alien hand syndrome

From Wikipedia, the free encyclopedia
 
Alien hand syndrome
Other namesAHS; alien limb syndrome; ALS; Dr. Strangelove syndrome
SpecialtyPsychiatry, Neurology

Alien hand syndrome (AHS) or Dr. Strangelove syndrome is a category of conditions in which a person experiences their limbs acting seemingly on their own, without conscious control over the actions. There are a variety of clinical conditions that fall under this category, which most commonly affects the left hand. There are many similar terms for the various forms of the condition, but they are often used inappropriately. The afflicted person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the controllable hand to restrain the alien hand. While under normal circumstances, thought, as intent, and action can be assumed to be deeply mutually entangled, the occurrence of alien hand syndrome can be usefully conceptualized as a phenomenon reflecting a functional "disentanglement" between thought and action.

Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain surgically separated, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy and epileptic psychosis, e.g., temporal lobe epilepsy. It also occurs in some cases after brain surgery, stroke, infection, tumor, aneurysm, migraine and specific degenerative brain conditions such as Alzheimer's disease, Corticobasal degeneration and Creutzfeldt–Jakob disease. Other areas of the brain that are associated with alien hand syndrome are the frontal, occipital, and parietal lobes.

Signs and symptoms

"Alien behavior" can be distinguished from reflexive behavior in that the former is flexibly purposive while the latter is obligatory. Sometimes the sufferer will not be aware of what the alien hand is doing until it is brought to his or her attention, or until the hand does something that draws their attention to its behavior. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in patients who have sustained damage to the corpus callosum that connects the two cerebral hemispheres (see also split-brain), the hands appear to be acting in opposition to each other.

A related syndrome described by the French neurologist François Lhermitte involves the release through disinhibition of a tendency to compulsively utilize objects that present themselves in the surrounding environment around the patient. The behavior of the patient is, in a sense, obligatorily linked to the "affordances" (using terminology introduced by the American ecological psychologist, James J. Gibson) presented by objects that are located within the immediate peri-personal environment.

This condition, termed "utilization behavior", is most often associated with extensive bilateral frontal lobe damage and might actually be thought of as "bilateral" alien hand syndrome in which the patient is compulsively directed by external environmental contingencies (e.g. the presence of a hairbrush on the table in front of them elicits the act of brushing the hair) and has no capacity to "hold back" and inhibit pre-potent motor programs that are obligatorily linked to the presence of specific external objects in the peri-personal space of the patient. When the frontal lobe damage is bilateral and generally more extensive, the patient completely loses the ability to act in a self-directed manner and becomes totally dependent upon the surrounding environmental indicators to guide his behavior in a general social context, a condition referred to as "environmental dependency syndrome".

In order to deal with the alien hand, some patients engage in personification of the affected hand. Usually these names are negative in nature, from mild such as "cheeky" to malicious "monster from the moon". For example, Doody and Jankovic described a patient who named her alien hand "baby Joseph". When the hand engaged in playful, troublesome activities such as pinching her nipples (akin to biting while nursing), she would experience amusement and would instruct baby Joseph to "stop being naughty". Furthermore, Bogen suggested that certain personality characteristics, such as a flamboyant personality, contribute to frequent personification of the affected hand.

Neuroimaging and pathological research shows that the frontal lobe (in the frontal variant) and corpus callosum (in the callosal variant) are the most common anatomical lesions responsible for the alien hand syndrome. These areas are closely linked in terms of motor planning and its final pathways.

The callosal variant includes advanced willed motor acts by the non-dominant hand, where patients frequently exhibit "intermanual conflict" in which one hand acts at cross-purposes with the other "good hand". For example, one patient was observed putting a cigarette into her mouth with her intact, "controlled" hand (her right, dominant hand), following which her alien, non-dominant, left hand came up to grasp the cigarette, pull the cigarette out of her mouth, and toss it away before it could be lit by the controlled, dominant, right hand. The patient then surmised that "I guess 'he' doesn't want me to smoke that cigarette." Another patient was observed to be buttoning up her blouse with her controlled dominant hand while the alien non-dominant hand, at the same time, was unbuttoning her blouse. The frontal variant most often affects the dominant hand, but can affect either hand depending on the lateralization of the damage to medial frontal cortex, and includes grasp reflex, impulsive groping toward objects or/and tonic grasping (i.e. difficulty in releasing grip).

In most cases, classic alien-hand signs derive from damage to the medial frontal cortex, accompanying damage to the corpus callosum. In these patients the main cause of damage is unilateral or bilateral infarction of cortex in the territory supplied by the anterior cerebral artery or associated arteries. Oxygenated blood is supplied by the anterior cerebral artery to most medial portions of the frontal lobes and to the anterior two-thirds of the corpus callosum, and infarction may consequently result in damage to multiple adjacent locations in the brain in the supplied territory. As the medial frontal lobe damage is often linked to lesions of the corpus callosum, frontal variant cases may also present with callosal form signs. Cases of damage restricted to the callosum however, tend not to show frontal alien-hand signs.

Cause

The common emerging factor in alien hand syndrome is that the primary motor cortex controlling hand movement is isolated from premotor cortex influences but remains generally intact in its ability to execute movements of the hand.

A 2009 fMRI study looking at the temporal sequence of activation of components of a cortical network associated with voluntary movement in normal individuals demonstrated "an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex". Therefore, with normal voluntary movement, the emergent sense of agency appears to be associated with an orderly sequence of activation that develops initially in the anteromedial frontal cortex in the vicinity of the supplementary motor complex on the medial surface of the frontal aspect of the hemisphere (including the supplementary motor area) prior to activation of the primary motor cortex in the pre-central gyrus on the lateral aspect of the hemisphere, when the hand movement is being generated. Activation of the primary motor cortex, presumed to be directly involved in the execution of the action via projections into the corticospinal component of the pyramidal tracts, is then followed by activation of the posterior parietal cortex, possibly related to the receipt of recurrent or re-afferent somatosensory feedback generated from the periphery by the movement which would normally interact with the efference copy transmitted from primary motor cortex to permit the movement to be recognized as self-generated rather than imposed by an external force. That is, the efference copy allows the recurrent afferent somatosensory flow from the periphery associated with the self-generated movement to be recognized as re-afference as distinct from ex-afference. Failure of this mechanism may lead to a failure to distinguish between self-generated and externally generated movement of the limb. This anomalous situation in which re-afference from a self-generated movement is mistakenly registered as ex-afference due to a failure to generate and successfully transmit an efference copy to sensory cortex, could readily lead to the interpretation that what is in actuality a self-generated movement has been produced by an external force as a result of the failure to develop a sense of agency in association with emergence of the self-generated movement (see below for a more detailed discussion).

A 2007 fMRI study examining the difference in functional brain activation patterns associated with alien as compared to non-alien "volitional" movement in a patient with alien hand syndrome found that alien movement involved anomalous isolated activation of the primary motor cortex in the damaged hemisphere contralateral to the alien hand, while non-alien movement involved the normal process of activation described in the preceding paragraph in which primary motor cortex in the intact hemisphere activates in concert with frontal premotor cortex and posterior parietal cortex presumably involved in a normal cortical network generating premotor influences on the primary motor cortex along with immediate post-motor re-afferent activation of the posterior parietal cortex.

Combining these two fMRI studies, one could hypothesize that the alien behavior that is unaccompanied by a sense of agency emerges due to autonomous activity in the primary motor cortex acting independently of premotor cortex pre-activating influences that would normally be associated with the emergence of a sense of agency linked to the execution of the action. 

As noted above, these ideas can also be linked to the concept of efference copy and re-afference, where efference copy is a signal postulated to be directed from premotor cortex (activated normally in the process associated with emergence of an internally generated movement) over to somatosensory cortex of the parietal region, in advance of the arrival of the "re-afferent" input generated from the moving limb, that is, the afferent return from the moving limb associated with the self-generated movement produced. It is generally thought that a movement is recognized as internally generated when the efference copy signal effectively "cancels out" the re-afference. The afferent return from the limb is effectively correlated with the efference copy signal so that the re-afference can be recognized as such and distinguished from "ex-afference", which would be afferent return from the limb produced by an externally imposed force. When the efference copy is no longer normally generated, then the afferent return from the limb associated with the self-generated movement is mis-perceived as externally produced "ex-afference" since it is no longer correlated with or canceled out by the efference copy. As a result, the development of the sense that a movement is not internally generated even though it actually is (i.e. the failure of the sense of agency to emerge in conjunction with the movement), could indicate a failure of the generation of the efference copy signal associated with the normal premotor process through which the movement is prepared for execution.

Since there is no disturbance of the sense of ownership of the limb (a concept discussed in the Wikipedia entry on sense of agency) in this situation, and there is no clearly apparent physically ostensible explanation for how the owned limb could be moving in a purposive manner without an associated sense of agency, effectively through its own power, a cognitive dissonance is created which may be resolved through the assumption that the goal-directed limb movement is being directed by an "alien" unidentifiable external force with the capacity for directing goal-directed actions of one's own limb.

Disconnection

It is theorized that alien hand syndrome results when disconnection occurs between different parts of the brain that are engaged in different aspects of the control of bodily movement. As a result, different regions of the brain are able to command bodily movements, but cannot generate a conscious feeling of self-control over these movements. As a result, the "sense of agency" that is normally associated with voluntary movement is impaired or lost. There is a dissociation between the process associated with the actual execution of the physical movements of the limb and the process that produces an internal sense of voluntary control over the movements, with this latter process thus normally creating the internal conscious sensation that the movements are being internally initiated, controlled and produced by an active self.

Recent studies have examined the neural correlates of emergence of the sense of agency under normal circumstances. This appears to involve consistent congruence between what is being produced through efferent outflow to the musculature of the body, and what is being sensed as the presumed product in the periphery of this efferent command signal. In alien hand syndrome, the neural mechanisms involved in establishing that this congruence has occurred may be impaired. This may involve an abnormality in the brain mechanism that differentiates between "re-afference" (i.e., the return of kinesthetic sensation from the self-generated "active" limb movement) and "ex-afference" (i.e., kinesthetic sensation generated from an externally produced 'passive' limb movement in which an active self does not participate). This brain mechanism is proposed to involve the production of a parallel "efference copy" signal that is sent directly to the somatic sensory regions and is transformed into a "corollary discharge", an expected afferent signal from the periphery that would result from the performance driven by the issued efferent signal. The correlation of the corollary discharge signal with the actual afferent signal returned from the periphery can then be used to determine if, in fact, the intended action occurred as expected. When the sensed result of the action is congruent with the predicted result, then the action can be labelled as self-generated and associated with an emergent sense of agency.

If, however, the neural mechanisms involved in establishing this sensorimotor linkage associated with self-generated action are faulty, it would be expected that the sense of agency with action would not develop as discussed in the previous section.

Loss of inhibitions

One theory posed to explain these phenomena proposes that the brain has separable neural "premotor" or "agency" systems for managing the process of transforming intentions into overt action. An anteromedial frontal premotor system is engaged in the process of directing exploratory actions based on "internal" drive by releasing or reducing inhibitory control over such actions.

A recent paper reporting on neuronal unit recording in the medial frontal cortex in human subjects showed a clear pre-activation of neurons identified in this area up to several hundred milliseconds prior to the onset of an overt self-generated finger movement and the authors were able to develop a computational model whereby volition emerges once a change in internally generated firing rate of neuronal assemblies in this part of the brain crossed a threshold. Damage to this anteromedial premotor system produces disinhibition and release of such exploratory and object acquisition actions which then occur autonomously. A posterolateral temporo-parieto-occipital premotor system has a similar inhibitory control over actions that withdraw from environmental stimuli as well as the ability to excite actions that are contingent upon and driven by external stimulation, as distinct from internal drive. These two intrahemispheric systems, each of which activates an opposing cortical "tropism", interact through mutual inhibition that maintains a dynamic balance between approaching toward (i.e. with "intent-to-capture" in which contact with and grasping onto the attended object is sought) versus withdrawing from (i.e. with "intent-to-escape" in which distancing from the attended object is sought) environmental stimuli in the behavior of the contralateral limbs. Together, these two intrahemispheric agency systems form an integrated trans-hemispheric agency system.

When the anteromedial frontal "escape" system is damaged, involuntary but purposive movements of an exploratory reach-and-grasp nature—what Denny-Brown referred to as a positive cortical tropism—are released in the contralateral limb. This is referred to as a positive cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that increases or enhances the eliciting stimulation through a positive feedback connection (see discussion above in section entitled "Parietal and Occipital Lobes").

When the posterolateral parieto-occipital "approach" system is damaged, involuntary purposive movements of a release-and-retract nature, such as levitation and instinctive avoidance – what Denny-Brown referred to as a negative cortical tropism – are released in the contralateral limb. This is referred to as a negative cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that reduces or eliminates the eliciting stimulation through a negative feedback connection (see discussion above in section entitled "Parietal and Occipital Lobes").

Each intrahemispheric agency system has the potential capability of acting autonomously in its control over the contralateral limb although unitary integrative control of the two hands is maintained through interhemispheric communication between these systems via the projections traversing the corpus callosum at the cortical level and other interhemispheric commissures linking the two hemispheres at the subcortical level.

Disconnection of hemispheres due to injury

One major difference between the two hemispheres is the direct connection between the agency system of the dominant hemisphere and the encoding system based primarily in the dominant hemisphere that links action to its production and through to its interpretation with language and language-encoded thought. The overarching unitary conscious agent that emerges in the intact brain is based primarily in the dominant hemisphere and is closely connected to the organization of language capacity. It is proposed that while relational action in the form of embodied inter-subjective behavior precedes linguistic capacity during infant development, a process ensues through the course of development through which linguistic constructs are linked to action elements in order to produce a language-based encoding of action-oriented knowledge.

When there is a major disconnection between the two hemispheres resulting from callosal injury, the language-linked dominant hemisphere agent which maintains its primary control over the dominant limb loses, to some degree, its direct and linked control over the separate "agent" based in the nondominant hemisphere, and the nondominant limb, which had been previously responsive and "obedient" to the dominant conscious agent. The possibility of purposeful action occurring outside of the realm of influence of the conscious dominant agent can occur and the basic assumption that both hands are controlled through and subject to the dominant agent is proven incorrect. The sense of agency that would normally arise from movement of the nondominant limb now no longer develops, or, at least, is no longer accessible to consciousness. A new explanatory narrative for understanding the situation in which the now inaccessible nondominant hemisphere based agent is capable of activating the nondominant limb is necessitated.

Under such circumstances, the two separated agents can control simultaneous actions in the two limbs that are directed at opposing purposes although the dominant hand remains linked to the dominant consciously accessible language-linked agent and is viewed as continuing to be under "conscious control" and obedient to conscious will and intent as accessible through thought, while the nondominant hand, directed by an essentially non-verbal agent whose intent can only be inferred by the dominant agent after the fact, is no longer "tied in" and subject to the dominant agent and is thus identified by the conscious language-based dominant agent as having a separate and inaccessible alien agency and associated existence. This theory would explain the emergence of alien behavior in the nondominant limb and intermanual conflict between the two limbs in the presence of damage to the corpus callosum.

The distinct anteromedial, frontal, and posterolateral temporo-parieto-occipital variants of the alien hand syndrome would be explained by selective injury to either the frontal or the posterior components of the agency systems within a particular hemisphere, with the relevant and specific form of alien behavior developing in the limb contralateral to the damaged hemisphere.

Diagnosis

Corpus callosum

Damage to the corpus callosum can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming alien, and the right hand will turn alien in the person with right-hemisphere dominance).

In "the callosal variant", the patient's hand counteracts voluntary actions performed by the other, "good" hand. Two phenomena that are often found in patients with callosal alien hand are agonistic dyspraxia and diagonistic dyspraxia.

Agonistic dyspraxia involves compulsive automatic execution of motor commands by one hand when the patient is asked to perform movements with the other hand. For example, when a patient with callosal damage was instructed to pull a chair forward, the affected hand would decisively and impulsively push the chair backwards. Agonistic dyspraxia can thus be viewed as an involuntary competitive interaction between the two hands directed toward completion of a desired act in which the affected hand competes with the unaffected hand to complete a purposive act originally intended to be performed by the unaffected hand.

Diagonistic dyspraxia, on the other hand, involves a conflict between the desired act in which the unaffected hand has been engaged and the interfering action of the affected hand which works to oppose the purpose of the desired act intended to be performed by the unaffected hand. For instance, when Akelaitis's patients underwent surgery to the corpus callosum to reduce epileptic seizures, one patient's left alien hand would frequently interfere with the right hand. For instance, while trying to turn over to the next page with the right hand, his left hand would try to close the book.

In another case of callosal alien hand, the patient did not suffer from intermanual conflict between the hands but rather from a symptom characterized by involuntary mirror movements of the affected hand. When the patient was asked to perform movements with one hand, the other hand would involuntarily perform a mirror image movement which continued even when the involuntary movement was brought to the attention of the patient, and the patient was asked to restrain the mirrored movement. The patient suffered from a ruptured aneurysm near the anterior cerebral artery, which resulted in the right hand being mirrored by the left hand. The patient described the left hand as frequently interfering and taking over anything the patient tried to do with the right hand. For instance, when trying to grasp a glass of water with the right hand with a right side approach, the left hand would involuntary reach out and grasp hold of the glass through a left side approach.

More recently, Geschwind et al. described the case of a woman who suffered severe coronary heart disease. One week after undergoing coronary artery bypass grafting, she noticed that her left hand started to "live a life of its own". It would unbutton her gown, try to choke her while asleep and would automatically fight with the right hand to answer the phone. She had to physically restrain the affected hand with the right hand to prevent injury, a behavior which has been termed "self-restriction". The left hand also showed signs of severe ideomotor apraxia. It was able to mimic actions but only with the help of mirror movements executed by the right hand (enabling synkinesis). Using magnetic resonance imaging (MRI), Geschwind et al. found damage to the posterior half of the callosal body, sparing the anterior half and the splenium extending slightly into the white matter underlying the right cingulate cortex.

Park et al. also described two cases of infarction as the origin of alien hand symptoms. Both individuals had suffered an infarction of the anterior cerebral artery (ACA). One individual, a 72 year-old male, had difficulty controlling his hands, as they often moved involuntarily, despite his trying to stabilize them. Furthermore, he often could not let go of objects after grasping them with his palms. The other individual, a 47 year-old female who suffered an ACA in a different location of the artery, complained that her left hand would move on its own and she could not control its movements. Her left hand could also sense when her right hand was holding an object and would involuntarily, forcibly take the object out of her right hand.

Frontal lobe

Unilateral injury to the medial aspect of the brain's frontal lobe can trigger reaching, grasping and other purposeful movements in the contralateral hand. With anteromedial frontal lobe injuries, these movements are often exploratory reaching movements in which external objects are frequently grasped and utilized functionally, without the simultaneous perception on the part of the patient that they are "in control" of these movements. Once an object has been acquired and is maintained in the grasp of this "frontal variant" form of alien hand, the patient often has difficulty with voluntarily releasing the object from grasp and can sometimes be seen to be peeling the fingers of the hand back off the grasped object using the opposite controlled hand to enable the release of the grasped object (also referred to as tonic grasping or the "instinctive grasp reaction"). Some (for example, the neurologist Derek Denny-Brown) have referred to this behavior as "magnetic apraxia"

Goldberg and Bloom described a woman who suffered a large cerebral infarction of the medial surface of the left frontal lobe in the territory of the left anterior cerebral artery which left her with the frontal variant of the alien hand involving the right hand. There were no signs of callosal disconnection nor was there evidence of any callosal damage. The patient displayed frequent grasp reflexes; her right hand would reach out and grab objects without releasing them. In regards to tonic grasping, the more the patient tried to let go of the object, the more the grip of the object tightened. With focused effort the patient was able to let go of the object, but if distracted, the behaviour would re-commence. The patient could also forcibly release the grasped object by peeling her fingers away from contact with the object using the intact left hand. Additionally, the hand would scratch at the patient's leg to the extent that an orthotic device was required to prevent injury. Another patient reported not only tonic grasping towards objects nearby, but the alien hand would take hold of the patient's penis and engage in public masturbation.

Parietal and occipital lobes

A distinct "posterior variant" form of alien hand syndrome is associated with damage to the posterolateral parietal lobe and/or occipital lobe of the brain. The movements in this situation tend to be more likely to withdraw the palmar surface of the hand away from sustained environmental contact rather than reaching out to grasp onto objects to produce palmar tactile stimulation, as is most often seen in the frontal form of the condition. In the frontal variant, tactile contact on the ventral surface of the palm and fingers facilitates finger flexion and grasp of the object through a positive feedback loop (i.e. the stimulus generates movement that reinforces, strengthens and sustains the triggering stimulation).

In contrast, in the posterior variant, tactile contact on the ventral surface of the palm and fingers is actively avoided through facilitation of extension of the fingers and withdrawal of the palm in a negative feedback loop (i.e. the stimulus, and even anticipation of stimulation of the palmar surface of the hand, generates movement of the palm and fingers that reduces and effectively counteracts and eliminates the triggering stimulation, or, in the case of anticipated palmar contact, decreases the likelihood of such contact). Alien movements in the posterior variant of the syndrome also tend to be less coordinated and show a coarse ataxic motion during active movement that is generally not observed in the frontal form of the condition. This is generally thought to be due to an optic form of ataxia since it is facilitated by the visual presence of an object with visual attention directed toward the object. The apparent instability could be due to an unstable interaction between the tactile avoidance tendency biasing toward withdrawal from the object, and the visually based acquisition bias tendency pushing toward an approach to the object.

The alien limb in the posterior variant of the syndrome may be seen to "levitate" upward into the air withdrawing away from contact surfaces through the activation of anti-gravity musculature. Alien hand movement in the posterior variant may show a typical posture, sometimes referred to as a "parietal hand" or the "instinctive avoidance reaction" (a term introduced by neurologist Derek Denny-Brown as an inverse form of the "magnetic apraxia" seen in the frontal variant, as noted above), in which the digits move into a highly extended position with active extension of the interphalangeal joints of the digits and hyper-extension of the metacarpophalangeal joints, and the palmar surface of the hand is actively pulled back away from approaching objects or up and away from supporting surfaces. The "alien" movements, however, remain purposeful and goal-directed, a point which clearly differentiates these movements from other disorganized non-purposeful forms of involuntary limb movement (e.g. athetosis, chorea, or myoclonus).

Similarities between frontal and posterior variants

In both the frontal and the posterior variants of the alien hand syndrome, the patient's reactions to the limb's apparent capability to perform goal-directed actions independent of conscious volition is similar. In both of these variants of alien hand syndrome, the alien hand emerges in the hand contralateral to the damaged hemisphere.

Treatment

There is no cure for the alien hand syndrome. However, the symptoms can be reduced and managed to some degree by keeping the alien hand occupied and involved in a task, for example by giving it an object to hold in its grasp. Specific learned tasks can restore voluntary control of the hand to a significant degree. One patient with the "frontal" form of alien hand who would reach out to grasp onto different objects (e.g., door handles) as he was walking was given a cane to hold in the alien hand while walking, even though he really did not need a cane for its usual purpose of assisting with balance and facilitating ambulation. With the cane firmly in the grasp of the alien hand, it would generally not release the grasp and drop the cane in order to reach out to grasp onto a different object. Other techniques proven to be effective includes; wedging the hand between the legs or slapping it; warm water application and visual or tactile contact. Additionally, Wu et al. found that an irritating alarm activated by biofeedback reduced the time the alien hand held an object.

In the presence of unilateral damage to a single cerebral hemisphere, there is generally a gradual reduction in the frequency of alien behaviors observed over time and a gradual restoration of voluntary control over the affected hand. Actually, when AHS originates from focal injury of acute onset, recovery usually occurs within a year. One theory is that neuroplasticity in the bihemispheric and subcortical brain systems involved in voluntary movement production can serve to re-establish the connection between the executive production process and the internal self-generation and registration process. Exactly how this may occur is not well understood, but a process of gradual recovery from alien hand syndrome when the damage is confined to a single cerebral hemisphere has been reported. In some instances, patients may resort to constraining the wayward, undesirable and sometimes embarrassing actions of the impaired hand by voluntarily grasping onto the forearm of the impaired hand using the intact hand. This observed behavior has been termed "self-restriction" or "self-grasping".

In another approach, the patient is trained to perform a specific task, such as moving the alien hand to contact a specific object or a highly salient environmental target, which is a movement that the patient can learn to generate voluntarily through focused training in order to effectively override the alien behavior. It is possible that some of this training produces a re-organization of premotor systems within the damaged hemisphere, or, alternatively, that ipsilateral control of the limb from the intact hemisphere may be expanded.

Another method involves simultaneously "muffling" the action of the alien hand and limiting the sensory feedback coming back to the hand from environmental contact by placing it in a restrictive "cloak" such as a specialized soft foam hand orthosis or, alternatively, an everyday oven mitt. Other patients have reported using an orthotic device to restrict perseverative grasping or restraining the alien hand by securing it to the bed pole. Of course, this can limit the degree to which the hand can participate in addressing functional goals for the patient and may be considered to be an unjustifiable restraint.
Theoretically, this approach could slow down the process through which voluntary control of the hand is restored if the neuroplasticity that underlies recovery involves the recurrent exercise of voluntary will to control the actions of the hand in a functional context and the associated experiential reinforcement through successful willful suppression of the alien behavior.

History

The first known case described in the medical literature appeared in a detailed case report published in German in 1908 by the preeminent German neuro-psychiatrist, Kurt Goldstein. In this paper, Goldstein described a right-handed woman who had suffered a stroke affecting her left side from which she had partially recovered by the time she was seen. However, her left arm seemed as though it belonged to another person and performed actions that appeared to occur independent of her will.

The patient complained of a feeling of "strangeness" in relationship to the goal-directed movements of the left hand and insisted that "someone else" was moving the left hand, and that she was not moving it herself. When the left hand grasped an object, she could not voluntarily release it. The senses of touch and proprioception of the left side were impaired. The left hand would make spontaneous movements, such as wiping the face or rubbing the eyes, but these were relatively infrequent. With significant effort, she was able to move her left arm in response to spoken command, but conscious movements were slower or less precise than similar involuntary motions.

Goldstein developed a "doctrine of motor apraxia" in which he discussed the generation of voluntary action and proposed a brain structure for temporal and spatial cognition, will and other higher cognitive processes. Goldstein maintained that a structure conceptually organizing both the body and external space was necessary for object perception as well as for voluntary action on external objects.
In his classic papers reviewing the wide variety of disconnection syndromes associated with focal brain pathology, Norman Geschwind commented that Kurt Goldstein "was perhaps the first to stress the non-unity of the personality in patients with callosal section, and its possible psychiatric effects".

In popular culture

  • In Stanley Kubrick's 1964 film Dr. Strangelove, the eponymous character played by Peter Sellers apparently suffers from alien hand syndrome, as he can't stop himself from doing the Nazi salute. "Dr. Strangelove syndrome" was suggested as the official name for AHS. This was not approved, though it is sometimes used as an alternative name.
  • In the 1999 American horror comedy film Idle Hands, the teenage boy protagonist finds out that his right hand has become possessed and is responsible for killing his parents and harming others.
  • In the House episode "Both Sides Now", a patient suffers from alien hand syndrome.
  • An episode of Dark Matters: Twisted But True—a documentary show on Discovery Science—described alien hand syndrome and traced its history.
  • The 2017 Indian Tamil dark comedy film Peechankai is about a person who suffers from AHS.
  • In Season 2 of Scream Queens, Dr. Brock Holt appears to suffer from alien hand syndrome.
  • An episode of the NPR show Invisibilia centers on a lady who developed alien hand syndrome after brain surgery.

Cooperative

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