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.
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.
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.
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 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.
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's “Society 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.
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 (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
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.
The title refers to the "fail-safe point" used by the Strategic Air Command (SAC) to prevent an SAC bomber from accidentally crossing into Soviet airspace and precipitating a nuclear war. In general, a fail safe
ensures that, as far as possible, the machine or process will not make
things worse in the event of something going wrong. The title's irony is
that the nature of SAC's fail-safe protocols could make things worse,
causing the event it was intended to prevent.
Plot summary
A US Air Force command center receives information that an unknown aircraft is approaching from Europe. The alert status of the Strategic Air Command's
(SAC) bomber forces is raised, a standard precaution against a sneak
attack. The unknown aircraft then disappears from radar, causing the
alert status to continue to increase, eventually leading to the bombers
being sent into the air to the fail-safe
points. From there, they can proceed to their targets only if they
receive a special attack code. After a short time, the unknown target is
re-acquired and identified as an airliner. The threat level is
immediately reduced, and the SAC fleet is sent a recall order.
A technical failure at the height of the alert allows the attack
code to be accidentally transmitted to Group Six, which consists of six
Vindicator supersonic bombers (footage of Convair B-58 Hustler
bombers is used in the film). Colonel Grady, the head of the group,
tries to contact Omaha to verify the fail-safe order (called Positive
Check), but Soviet radio jamming prevents Grady from hearing them.
Concluding that the fail-safe order and the radio jamming could mean
only nuclear war, Grady orders the Group Six crew towards Moscow, their intended destination.
At meetings in Omaha, at the Pentagon, and in the fallout shelter of the White House,
American politicians and scholars debate the implications of the
attack. Professor Groteschele, a civilian adviser, suggests that the
United States follow this accidental attack with a full-scale attack to
force the Soviets to surrender. The President of the United States (unnamed but apparently modeled on John F. Kennedy) refuses to consider such a course of action.
Instead, the President orders the Air Force to shoot down the
bombers. Air Force brass protest, stating that the fighters cannot
easily catch the bombers and will run out of fuel over the Arctic Ocean in the attempt. The President orders them to try anyway, and the six "Skyscrapper" supersonic fighters (F-104 Starfighter-like aircraft) in the area engage their afterburners and fire their rockets in an attempt to hit the bombers. The fighters crash into the sea, and the pilots are lost.
The President contacts the Premier of the Soviet Union, identified in the book as Nikita Khrushchev,
and offers assistance in attacking the group. The Soviets decline at
first; however, they soon decide to accept it. At SAC headquarters, a
fight breaks out over the very idea of working with the Soviets to shoot
down their own aircraft. Air Force General Bogan attempts to stop the
attack, but his executive officer, Colonel Cascio, wants it to continue.
Cascio attempts to take over command of SAC, but is stopped by the Air Police. However, precious time has been wasted.
Meanwhile, the Soviet PVO Strany
air defense corps has managed to shoot down two of the six planes. The
Soviets accept American help and shoot down a third plane. Two bombers
and a support plane remain on course to Moscow. Bogan tells Marshal
Nevsky, the Soviet commander, to ignore Plane #6 (the support plane)
because it has no weapons. Nevsky, who mistrusts Bogan, instead orders
his Soviet aircraft to attack all three planes. Plane 6's last feint
guarantees that the two remaining bombers can successfully attack.
Following the failure, Nevsky collapses.
As the two planes approach Moscow, Colonel Grady uses the radio
to contact SAC to inform them that they are about to make the strike. As
a last-minute measure, the Soviets fire a barrage of nuclear-tipped
missiles to form a fireball in an attempt to knock the low-flying
Vindicator out of the sky. The Vindicators shoot up one last decoy,
which successfully leads the Soviet missiles high in the air. However,
one missile explodes earlier than expected; the second bomber blows up,
but Colonel Grady's plane survives. With the radio channel still open,
the President attempts to persuade Grady that there is no war. Believing
that such a late recall attempt must be a Soviet trick, Grady ignores
them.
The nearby explosion of the Soviet missiles has given the bomber
crew a huge radiation dose, and Grady tells his crew, "We're not just
walking wounded, we're walking dead men." He intends to fly the aircraft
over Moscow and detonate the bombs in the plane. His co-pilot agrees,
noting, "There's nothing to go home to" under the belief that the United
States has already been devastated by a full-scale nuclear attack from
the Soviet Union.
When it becomes apparent that one bomber will get through Soviet
defenses and destroy Moscow, the American President states that he will
order an American bomber to destroy New York City at the same time, with the Empire State Building as ground zero;
that also involves a grave personal sacrifice, as the First Lady is
visiting New York, and the President decides not to warn her. On hearing
this, the supposedly atheist Communist leader bursts out with "Holy Mother of God!"
He is appalled but realizes that it is the only way to prevent a
worldwide nuclear war which will probably destroy humanity as "others"
(presumably the Soviet military) would not accept the unilateral
destruction of Moscow, and would depose him and retaliate. The bomb is
dropped by a senior general within SAC, who orders his crew to let him
handle the entire bombing run by himself to assume all the
responsibility; he then takes his own life.
