Reticular formation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Reticular_formation 

 

Reticular formation
Coronal section of the pons, at its upper part. (Formatio reticularis labeled at left.)
Traverse section of the medulla oblongata at about the middle of the olive. (Formatio reticularis grisea and formatio reticularis alba labeled at left.)
Details
Location	Brainstem
Identifiers
Latin	formatio reticularis
MeSH	D012154
NeuroNames	1223
NeuroLex ID	nlx_143558
TA98	A14.1.00.021 A14.1.05.403 A14.1.06.327
TA2	5367
FMA	77719

The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation make up a complex set of networks in the core of the brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata. The reticular formation includes ascending pathways to the cortex in the ascending reticular activating system (ARAS) and descending pathways to the spinal cord via the reticulospinal tracts.

Neurons of the reticular formation, particularly those of the ascending reticular activating system, play a crucial role in maintaining behavioral arousal and consciousness. The overall functions of the reticular formation are modulatory and premotor, involving somatic motor control, cardiovascular control, pain modulation, sleep and consciousness, and habituation. The modulatory functions are primarily found in the rostral sector of the reticular formation and the premotor functions are localized in the neurons in more caudal regions.

The reticular formation is divided into three columns: raphe nuclei (median), gigantocellular reticular nuclei (medial zone), and parvocellular reticular nuclei (lateral zone). The raphe nuclei are the place of synthesis of the neurotransmitter serotonin, which plays an important role in mood regulation. The gigantocellular nuclei are involved in motor coordination. The parvocellular nuclei regulate exhalation.

The reticular formation is essential for governing some of the basic functions of higher organisms and is one of the phylogenetically oldest portions of the brain.

Structure

A cross section of the lower part of the pons showing the pontine reticular formation labeled as #9

The human reticular formation is composed of almost 100 brain nuclei and contains many projections into the forebrain, brainstem, and cerebellum, among other regions. It includes the reticular nuclei, reticulothalamic projection fibers, diffuse thalamocortical projections, ascending cholinergic projections, descending non-cholinergic projections, and descending reticulospinal projections. The reticular formation also contains two major neural subsystems, the ascending reticular activating system and descending reticulospinal tracts, which mediate distinct cognitive and physiological processes. It has been functionally cleaved both sagittally and coronally.

Traditionally the reticular nuclei are divided into three columns:

• In the median column – the raphe nuclei
• In the medial column – gigantocellular nuclei (because of larger size of the cells)
• In the lateral column – parvocellular nuclei (because of smaller size of the cells)

The original functional differentiation was a division of caudal and rostral. This was based upon the observation that the lesioning of the rostral reticular formation induces a hypersomnia in the cat brain. In contrast, lesioning of the more caudal portion of the reticular formation produces insomnia in cats. This study has led to the idea that the caudal portion inhibits the rostral portion of the reticular formation.

Sagittal division reveals more morphological distinctions. The raphe nuclei form a ridge in the middle of the reticular formation, and, directly to its periphery, there is a division called the medial reticular formation. The medial RF is large and has long ascending and descending fibers, and is surrounded by the lateral reticular formation. The lateral RF is close to the motor nuclei of the cranial nerves, and mostly mediates their function.

Medial and lateral reticular formation

The medial reticular formation and lateral reticular formation are two columns of nuclei with ill-defined boundaries that send projections through the medulla and into the midbrain. The nuclei can be differentiated by function, cell type, and projections of efferent or afferent nerves. Moving caudally from the rostral midbrain, at the site of the rostral pons and the midbrain, the medial RF becomes less prominent, and the lateral RF becomes more prominent.

Existing on the sides of the medial reticular formation is its lateral cousin, which is particularly pronounced in the rostral medulla and caudal pons. Out from this area spring the cranial nerves, including the very important vagus nerve. The lateral RF is known for its ganglions and areas of interneurons around the cranial nerves, which serve to mediate their characteristic reflexes and functions.

Function

The reticular formation consists of more than 100 small neural networks, with varied functions including the following:

1. Somatic motor control – Some motor neurons send their axons to the reticular formation nuclei, giving rise to the reticulospinal tracts of the spinal cord. These tracts function in maintaining tone, balance, and posture – especially during body movements. The reticular formation also relays eye and ear signals to the cerebellum so that the cerebellum can integrate visual, auditory, and vestibular stimuli in motor coordination. Other motor nuclei include gaze centers, which enable the eyes to track and fixate objects, and central pattern generators, which produce rhythmic signals of breathing and swallowing.
2. Cardiovascular control – The reticular formation includes the cardiac and vasomotor centers of the medulla oblongata.
3. Pain modulation – The reticular formation is one means by which pain signals from the lower body reach the cerebral cortex. It is also the origin of the descending analgesic pathways. The nerve fibers in these pathways act in the spinal cord to block the transmission of some pain signals to the brain.
4. Sleep and consciousness – The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert some control over which sensory signals reach the cerebrum and come to our conscious attention. It plays a central role in states of consciousness like alertness and sleep. Injury to the reticular formation can result in irreversible coma.
5. Habituation – This is a process in which the brain learns to ignore repetitive, meaningless stimuli while remaining sensitive to others. A good example of this is a person who can sleep through loud traffic in a large city, but is awakened promptly due to the sound of an alarm or crying baby. Reticular formation nuclei that modulate activity of the cerebral cortex are part of the ascending reticular activating system.

Major subsystems

Ascending reticular activating system

Ascending reticular activating system. Reticular formation labeled near center.

The ascending reticular activating system (ARAS), also known as the extrathalamic control modulatory system or simply the reticular activating system (RAS), is a set of connected nuclei in the brains of vertebrates that is responsible for regulating wakefulness and sleep-wake transitions. The ARAS is a part of the reticular formation and is mostly composed of various nuclei in the thalamus and a number of dopaminergic, noradrenergic, serotonergic, histaminergic, cholinergic, and glutamatergic brain nuclei.

Structure of the ARAS

The ARAS is composed of several neural circuits connecting the dorsal part of the posterior midbrain and anterior pons to the cerebral cortex via distinct pathways that project through the thalamus and hypothalamus. The ARAS is a collection of different nuclei – more than 20 on each side in the upper brainstem, the pons, medulla, and posterior hypothalamus. The neurotransmitters that these neurons release include dopamine, norepinephrine, serotonin, histamine, acetylcholine, and glutamate. They exert cortical influence through direct axonal projections and indirect projections through thalamic relays.

The thalamic pathway consists primarily of cholinergic neurons in the pontine tegmentum, whereas the hypothalamic pathway is composed primarily of neurons that release monoamine neurotransmitters, namely dopamine, norepinephrine, serotonin, and histamine. The glutamate-releasing neurons in the ARAS were identified much more recently relative to the monoaminergic and cholinergic nuclei; the glutamatergic component of the ARAS includes one nucleus in the hypothalamus and various brainstem nuclei. The orexin neurons of the lateral hypothalamus innervate every component of the ascending reticular activating system and coordinate activity within the entire system.

The ARAS consists of evolutionarily ancient areas of the brain, which are crucial to the animal's survival and protected during adverse periods, such as during inhibitory periods of Totsellreflex, aka, "animal hypnosis". The ascending reticular activating system which sends neuromodulatory projections to the cortex - mainly connects to the prefrontal cortex. There seems to be low connectivity to the motor areas of the cortex.

Functions of the ARAS

Consciousness

The ascending reticular activating system is an important enabling factor for the state of consciousness. The ascending system is seen to contribute to wakefulness as characterised by cortical and behavioural arousal.

Regulating sleep-wake transitions

Further information: Neuroscience of sleep

The main function of the ARAS is to modify and potentiate thalamic and cortical function such that electroencephalogram (EEG) desynchronization ensues. There are distinct differences in the brain's electrical activity during periods of wakefulness and sleep: Low voltage fast burst brain waves (EEG desynchronization) are associated with wakefulness and REM sleep (which are electrophysiologically similar); high voltage slow waves are found during non-REM sleep. Generally speaking, when thalamic relay neurons are in burst mode the EEG is synchronized and when they are in tonic mode it is desynchronized. Stimulation of the ARAS produces EEG desynchronization by suppressing slow cortical waves (0.3–1 Hz), delta waves (1–4 Hz), and spindle wave oscillations (11–14 Hz) and by promoting gamma band (20–40 Hz) oscillations.

The physiological change from a state of deep sleep to wakefulness is reversible and mediated by the ARAS. The ventrolateral preoptic nucleus (VLPO) of the hypothalamus inhibits the neural circuits responsible for the awake state, and VLPO activation contributes to the sleep onset. During sleep, neurons in the ARAS will have a much lower firing rate; conversely, they will have a higher activity level during the waking state. In order that the brain may sleep, there must be a reduction in ascending afferent activity reaching the cortex by suppression of the ARAS.

Attention

The ARAS also helps mediate transitions from relaxed wakefulness to periods of high attention. There is increased regional blood flow (presumably indicating an increased measure of neuronal activity) in the midbrain reticular formation (MRF) and thalamic intralaminar nuclei during tasks requiring increased alertness and attention.

Clinical significance of the ARAS

Mass lesions in brainstem ARAS nuclei can cause severe alterations in level of consciousness (e.g., coma). Bilateral damage to the reticular formation of the midbrain may lead to coma or death.

Direct electrical stimulation of the ARAS produces pain responses in cats and elicits verbal reports of pain in humans. Ascending reticular activation in cats can produce mydriasis, which can result from prolonged pain. These results suggest some relationship between ARAS circuits and physiological pain pathways.

Pathologies

Some pathologies of the ARAS may be attributed to age, as there appears to be a general decline in reactivity of the ARAS with advancing years. Changes in electrical coupling have been suggested to account for some changes in ARAS activity: if coupling were down-regulated, there would be a corresponding decrease in higher-frequency synchronization (gamma band). Conversely, up-regulated electrical coupling would increase synchronization of fast rhythms that could lead to increased arousal and REM sleep drive. Specifically, disruption of the ARAS has been implicated in the following disorders:

• Narcolepsy: Lesions along the pedunculopontine (PPT/PPN) / laterodorsal tegmental (LDT) nuclei are associated with narcolepsy. There is a significant down-regulation of PPN output and a loss of orexin peptides, promoting the excessive daytime sleepiness that is characteristic of this disorder.
• Progressive supranuclear palsy (PSP) : Dysfunction of nitrous oxide signaling has been implicated in the development of PSP.
• Parkinson's disease: REM sleep disturbances are common in Parkinson's. It is mainly a dopaminergic disease, but cholinergic nuclei are depleted as well. Degeneration in the ARAS begins early in the disease process.

Developmental influences

There are several potential factors that may adversely influence the development of the ascending reticular activating system:

• Preterm birth: Regardless of birth weight or weeks of gestation, premature birth induces persistent deleterious effects on pre-attentional (arousal and sleep-wake abnormalities), attentional (reaction time and sensory gating), and cortical mechanisms throughout development.
• Smoking during pregnancy: Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. This exposure can induce up-regulation of α4β2 nicotinic receptors on cells of the pedunculopontine nucleus (PPN), resulting in increased tonic activity, resting membrane potential, and hyperpolarization-activated cation current. These major disturbances of the intrinsic membrane properties of PPN neurons result in increased levels of arousal and sensory gating, deficits (demonstrated by a diminished amount of habituation to repeated auditory stimuli). It is hypothesized that these physiological changes may intensify attentional dysregulation later in life.

Descending reticulospinal tracts

Spinal cord tracts - reticulospinal tract labeled in red, near-center at left in figure

The reticulospinal tracts, also known as the descending or anterior reticulospinal tracts, are extrapyramidal motor tracts that descend from the reticular formation in two tracts to act on the motor neurons supplying the trunk and proximal limb flexors and extensors. The reticulospinal tracts are involved mainly in locomotion and postural control, although they do have other functions as well. The descending reticulospinal tracts are one of four major cortical pathways to the spinal cord for musculoskeletal activity. The reticulospinal tracts works with the other three pathways to give a coordinated control of movement, including delicate manipulations. The four pathways can be grouped into two main system pathways – a medial system and a lateral system. The medial system includes the reticulospinal pathway and the vestibulospinal pathway, and this system provides control of posture. The corticospinal and the rubrospinal tract pathways belong to the lateral system which provides fine control of movement.

Medial and lateral tracts

This descending tract is divided into two parts, the medial (or pontine) and lateral (or medullary) reticulospinal tracts (MRST and LRST).

• The medial reticulospinal tract is responsible for exciting anti-gravity, extensor muscles. The fibers of this tract arise from the caudal pontine reticular nucleus and the oral pontine reticular nucleus and project to lamina VII and lamina VIII of the spinal cord.
• The lateral reticulospinal tract is responsible for inhibiting excitatory axial extensor muscles of movement. It is also responsible for automatic breathing. The fibers of this tract arise from the medullary reticular formation, mostly from the gigantocellular nucleus, and descend the length of the spinal cord in the anterior part of the lateral column. The tract terminates in lamina VII mostly with some fibers terminating in lamina IX of the spinal cord.

The ascending sensory tract conveying information in the opposite direction is known as the spinoreticular tract.

Functions of the reticulospinal tracts

1. Integrates information from the motor systems to coordinate automatic movements of locomotion and posture
2. Facilitates and inhibits voluntary movement; influences muscle tone
3. Mediates autonomic functions
4. Modulates pain impulses
5. Influences blood flow to lateral geniculate nucleus of the thalamus.

Clinical significance of the reticulospinal tracts

The reticulospinal tracts provide a pathway by which the hypothalamus can control sympathetic thoracolumbar outflow and parasympathetic sacral outflow.

Two major descending systems carrying signals from the brainstem and cerebellum to the spinal cord can trigger automatic postural response for balance and orientation: vestibulospinal tracts from the vestibular nuclei and reticulospinal tracts from the pons and medulla. Lesions of these tracts result in profound ataxia and postural instability.

Physical or vascular damage to the brainstem disconnecting the red nucleus (midbrain) and the vestibular nuclei (pons) may cause decerebrate rigidity, which has the neurological sign of increased muscle tone and hyperactive stretch reflexes. Responding to a startling or painful stimulus, both arms and legs extend and turn internally. The cause is the tonic activity of lateral vestibulospinal and reticulospinal tracts stimulating extensor motoneurons without the inhibitions from rubrospinal tract.

Brainstem damage above the red nucleus level may cause decorticate rigidity. Responding to a startling or painful stimulus, the arms flex and the legs extend. The cause is the red nucleus, via the rubrospinal tract, counteracting the extensor motorneuron's excitation from the lateral vestibulospinal and reticulospinal tracts. Because the rubrospinal tract only extends to the cervical spinal cord, it mostly acts on the arms by exciting the flexor muscles and inhibiting the extensors, rather than the legs.

Damage to the medulla below the vestibular nuclei may cause flaccid paralysis, hypotonia, loss of respiratory drive, and quadriplegia. There are no reflexes resembling early stages of spinal shock because of complete loss of activity in the motorneurons, as there is no longer any tonic activity arising from the lateral vestibulospinal and reticulospinal tracts.

History

The term "reticular formation" was coined in the late 19th century by Otto Deiters, coinciding with Ramon y Cajal's neuron doctrine. Allan Hobson states in his book The Reticular Formation Revisited that the name is an etymological vestige from the fallen era of the aggregate field theory in the neural sciences. The term "reticulum" means "netlike structure", which is what the reticular formation resembles at first glance. It has been described as being either too complex to study or an undifferentiated part of the brain with no organization at all. Eric Kandel describes the reticular formation as being organized in a similar manner to the intermediate gray matter of the spinal cord. This chaotic, loose, and intricate form of organization is what has turned off many researchers from looking farther into this particular area of the brain. The cells lack clear ganglionic boundaries, but do have clear functional organization and distinct cell types. The term "reticular formation" is seldom used anymore except to speak in generalities. Modern scientists usually refer to the individual nuclei that compose the reticular formation.

Moruzzi and Magoun first investigated the neural components regulating the brain's sleep-wake mechanisms in 1949. Physiologists had proposed that some structure deep within the brain controlled mental wakefulness and alertness. It had been thought that wakefulness depended only on the direct reception of afferent (sensory) stimuli at the cerebral cortex.

As direct electrical stimulation of the brain could simulate electrocortical relays, Magoun used this principle to demonstrate, on two separate areas of the brainstem of a cat, how to produce wakefulness from sleep. He first stimulated the ascending somatic and auditory paths; second, a series of "ascending relays from the reticular formation of the lower brain stem through the midbrain tegmentum, subthalamus and hypothalamus to the internal capsule." The latter was of particular interest, as this series of relays did not c.[orrespond to any known anatomical pathways for the wakefulness signal transduction and was coined the ascending reticular activating system (ARAS).

Next, the significance of this newly identified relay system was evaluated by placing lesions in the medial and lateral portions of the front of the midbrain. Cats with mesencephalic interruptions to the ARAS entered into a deep sleep and displayed corresponding brain waves. In alternative fashion, cats with similarly placed interruptions to ascending auditory and somatic pathways exhibited normal sleeping and wakefulness, and could be awakened with physical stimuli. Because these external stimuli would be blocked on their way to the cortex by the interruptions, this indicated that the ascending transmission must travel through the newly discovered ARAS.

Finally, Magoun recorded potentials within the medial portion of the brain stem and discovered that auditory stimuli directly fired portions of the reticular activating system. Furthermore, single-shock stimulation of the sciatic nerve also activated the medial reticular formation, hypothalamus, and thalamus. Excitation of the ARAS did not depend on further signal propagation through the cerebellar circuits, as the same results were obtained following decerebellation and decortication. The researchers proposed that a column of cells surrounding the midbrain reticular formation received input from all the ascending tracts of the brain stem and relayed these afferents to the cortex and therefore regulated wakefulness.

Hallucination

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hallucination 

Hallucination
My eyes at the moment of the apparitions by August Natterer, a German artist who created many drawings of his hallucinations
Specialty	Psychiatry
Symptoms	Visual, Auditory, Gustatory, Olfactory, and Tactile Hallucinations.
Duration	In people with Brief Psychotic Disorder, it lasts for less than one month. Schizophrenic Hallucinations may be lifelong in the absence of treatment.
Deaths	Unknown. (Mostly caused by Auditory Hallucinations commanding the affected person to act out actions that are harmful to oneself or others).

A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combination of two conscious states of brain wakefulness and REM sleep. They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance. Many hallucinations happen also during sleep paralysis.

Hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Hallucinations are referred to as multimodal if multiple sensory modalities occur.

A mild form of hallucination is known as a disturbance, and can occur in most of the senses above. These may be things like seeing movement in peripheral vision, or hearing faint noises or voices. Auditory hallucinations are very common in schizophrenia. They may be benevolent (telling the subject good things about themselves) or malicious, cursing the subject. 55% of auditory hallucinations are malicious in content, for example, people talking about the subject, not speaking to them directly. Like auditory hallucinations, the source of the visual counterpart can also be behind the subject. This can produce a feeling of being looked or stared at, usually with malicious intent. Frequently, auditory hallucinations and their visual counterpart are experienced by the subject together.

Hypnagogic hallucinations and hypnopompic hallucinations are considered normal phenomena. Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Hallucinations can be associated with drug use (particularly deliriants), sleep deprivation, psychosis, neurological disorders, and delirium tremens.

The word "hallucination" itself was introduced into the English language by the 17th-century physician Sir Thomas Browne in 1646 from the derivation of the Latin word alucinari meaning to wander in the mind. For Browne, hallucination means a sort of vision that is "depraved and receive[s] its objects erroneously".

Classification

Hallucinations may be manifested in a variety of forms. Various forms of hallucinations affect different senses, sometimes occurring simultaneously, creating multiple sensory hallucinations for those experiencing them.

Auditory

Main article: Auditory hallucination

Auditory hallucinations (also known as paracusia) are the perception of sound without outside stimulus. Auditory hallucinations can be divided into elementary and complex, along with verbal and nonverbal. These hallucinations are the most common type of hallucination, with auditory verbal hallucinations being more common than nonverbal. Elementary hallucinations are the perception of sounds such as hissing, whistling, an extended tone, and more. In many cases, tinnitus is an elementary auditory hallucination. However, some people who experience certain types of tinnitus, especially pulsatile tinnitus, are actually hearing the blood rushing through vessels near the ear. Because the auditory stimulus is present in this situation, it does not qualify it as a hallucination.

Complex hallucinations are those of voices, music, or other sounds that may or may not be clear, may or may not be familiar, and may be friendly, aggressive, or among other possibilities. A hallucination of a single individual person of one or more talking voices is particularly associated with psychotic disorders such as schizophrenia, and hold special significance in diagnosing these conditions.

In schizophrenia voices are normally perceived coming from outside the person but in dissociative disorders they are perceived as originating from within the person, commenting in their head instead of behind their back. Differential diagnosis between schizophrenia and dissociative disorders is challenging due to many overlapping symptoms, especially Schneiderian first rank symptoms such as hallucinations. However, many people who do not have a diagnosable mental illness may sometimes hear voices as well. One important example to consider when forming a differential diagnosis for a patient with paracusia is lateral temporal lobe epilepsy. Despite the tendency to associate hearing voices, or otherwise hallucinating, and psychosis with schizophrenia or other psychiatric illnesses, it is crucial to take into consideration that, even if a person does exhibit psychotic features, they do not necessarily have a psychiatric disorder on its own. Disorders such as Wilson's disease, various endocrine diseases, numerous metabolic disturbances, multiple sclerosis, systemic lupus erythematosus, porphyria, sarcoidosis, and many others can present with psychosis.

Musical hallucinations are also relatively common in terms of complex auditory hallucinations and may be the result of a wide range of causes ranging from hearing-loss (such as in musical ear syndrome, the auditory version of Charles Bonnet syndrome), lateral temporal lobe epilepsy, arteriovenous malformation, stroke, lesion, abscess, or tumor.

The Hearing Voices Movement is a support and advocacy group for people who hallucinate voices, but do not otherwise show signs of mental illness or impairment.

High caffeine consumption has been linked to an increase in likelihood of one experiencing auditory hallucinations. A study conducted by the La Trobe University School of Psychological Sciences revealed that as few as five cups of coffee a day (approximately 500 mg of caffeine) could trigger the phenomenon.

Visual

See also: Visual hallucinations in psychosis, Pareidolia, and Palinopsia

A visual hallucination is "the perception of an external visual stimulus where none exists". A separate but related phenomenon is a visual illusion, which is a distortion of a real external stimulus. Visual hallucinations are classified as simple or complex:

• Simple visual hallucinations (SVH) are also referred to as non-formed visual hallucinations and elementary visual hallucinations. These terms refer to lights, colors, geometric shapes, and indiscrete objects. These can be further subdivided into phosphenes which are SVH without structure, and photopsias which are SVH with geometric structures.
• Complex visual hallucinations (CVH) are also referred to as formed visual hallucinations. CVHs are clear, lifelike images or scenes such as people, animals, objects, places, etc.

For example, one may report hallucinating a giraffe. A simple visual hallucination is an amorphous figure that may have a similar shape or color to a giraffe (looks like a giraffe), while a complex visual hallucination is a discrete, lifelike image that is, unmistakably, a giraffe.

Command

See also: Bicameral mentality

Command hallucinations are hallucinations in the form of commands; they appear to be from an external source, or can appear coming from the subject's head. The contents of the hallucinations can range from the innocuous to commands to cause harm to the self or others. Command hallucinations are often associated with schizophrenia. People experiencing command hallucinations may or may not comply with the hallucinated commands, depending on the circumstances. Compliance is more common for non-violent commands.

Command hallucinations are sometimes used to defend a crime that has been committed, often homicides. In essence, it is a voice that one hears and it tells the listener what to do. Sometimes the commands are quite benign directives such as "Stand up" or "Shut the door." Whether it is a command for something simple or something that is a threat, it is still considered a "command hallucination." Some helpful questions that can assist one in determining if they may have this includes: "What are the voices telling you to do?", "When did your voices first start telling you to do things?", "Do you recognize the person who is telling you to harm yourself (or others)?", "Do you think you can resist doing what the voices are telling you to do?"

Olfactory

Main articles: Phantosmia and Parosmia

Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered, are distortions to the sense of smell (olfactory system), and in most cases, are not caused by anything serious and will usually go away on their own in time. It can result from a range of conditions such as nasal infections, nasal polyps, dental problems, migraines, head injuries, seizures, strokes, or brain tumors. Environmental exposures can sometimes cause it as well, such as smoking, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication, substance withdrawal, or psychotic disorders (e.g., schizophrenia). The perceived odors are usually unpleasant and commonly described as smelling burned, foul, spoiled, or rotten.

Tactile

Main article: Tactile hallucination

Tactile hallucinations are the illusion of tactile sensory input, simulating various types of pressure to the skin or other organs. One subtype of tactile hallucination, formication, is the sensation of insects crawling underneath the skin and is frequently associated with prolonged cocaine use. However, formication may also be the result of normal hormonal changes such as menopause, or disorders such as peripheral neuropathy, high fevers, Lyme disease, skin cancer, and more.

Gustatory

This type of hallucination is the perception of taste without a stimulus. These hallucinations, which are typically strange or unpleasant, are relatively common among individuals who have certain types of focal epilepsy, especially temporal lobe epilepsy. The regions of the brain responsible for gustatory hallucination in this case are the insula and the superior bank of the sylvian fissure.

General somatic sensations

General somatic sensations of a hallucinatory nature are experienced when an individual feels that their body is being mutilated, i.e. twisted, torn, or disemboweled. Other reported cases are invasion by animals in the person's internal organs, such as snakes in the stomach or frogs in the rectum. The general feeling that one's flesh is decomposing is also classified under this type of this hallucination.

Multimodal

A hallucination involving sensory modalities is called multimodal, analogous to unimodal hallucinations which have only one sensory modality. The multiple sensory modalities can occur at the same time (simultaneously) or with a delay (serial), be related or unrelated to each other, and be consistent with reality (congruent) or not (incongruent). For example, a person talking in a hallucination would be congruent with reality, but a cat talking would not be.

Multimodal hallucinations are correlated to poorer mental health outcomes, and are often experienced as feeling more real.

Cause

See also: Psychosis (causes)

Hallucinations can be caused by a number of factors.

Hypnagogic hallucination

Main article: Hypnagogia

These hallucinations occur just before falling asleep and affect a high proportion of the population: in one survey 37% of the respondents experienced them twice a week. The hallucinations can last from seconds to minutes; all the while, the subject usually remains aware of the true nature of the images. These may be associated with narcolepsy. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.

Peduncular hallucinosis

Main article: Peduncular hallucinosis

Peduncular means pertaining to the peduncle, which is a neural tract running to and from the pons on the brain stem. These hallucinations usually occur in the evenings, but not during drowsiness, as in the case of hypnagogic hallucination. The subject is usually fully conscious and then can interact with the hallucinatory characters for extended periods of time. As in the case of hypnagogic hallucinations, insight into the nature of the images remains intact. The false images can occur in any part of the visual field, and are rarely polymodal.

Delirium tremens

Main article: Delirium tremens

One of the more enigmatic forms of visual hallucination is the highly variable, possibly polymodal delirium tremens. Individuals with delirium tremens may be agitated and confused, especially in the later stages of this disease. Insight is gradually reduced with the progression of this disorder. Sleep is disturbed and occurs for a shorter period of time, with rapid eye movement sleep.

Parkinson's disease and Lewy body dementia

Parkinson's disease is linked with Lewy body dementia for their similar hallucinatory symptoms. The symptoms strike during the evening in any part of the visual field, and are rarely polymodal. The segue into hallucination may begin with illusions where sensory perception is greatly distorted, but no novel sensory information is present. These typically last for several minutes, during which time the subject may be either conscious and normal or drowsy/inaccessible. Insight into these hallucinations is usually preserved and REM sleep is usually reduced. Parkinson's disease is usually associated with a degraded substantia nigra pars compacta, but recent evidence suggests that PD affects a number of sites in the brain. Some places of noted degradation include the median raphe nuclei, the noradrenergic parts of the locus coeruleus, and the cholinergic neurons in the parabrachial area and pedunculopontine nuclei of the tegmentum.

Migraine coma

See also: Migraine aura and Scintillating scotoma

This type of hallucination is usually experienced during the recovery from a comatose state. The migraine coma can last for up to two days, and a state of depression is sometimes comorbid. The hallucinations occur during states of full consciousness, and insight into the hallucinatory nature of the images is preserved. It has been noted that ataxic lesions accompany the migraine coma.

Charles Bonnet syndrome

Charles Bonnet syndrome is the name given to visual hallucinations experienced by a partially or severely sight impaired person. The hallucinations can occur at any time and can distress people of any age, as they may not initially be aware that they are hallucinating. They may fear for their own mental health initially, which may delay them sharing with carers until they start to understand it themselves. The hallucinations can frighten and disconcert as to what is real and what is not. The hallucinations can sometimes be dispersed by eye movements, or by reasoned logic such as, "I can see fire but there is no smoke and there is no heat from it" or perhaps, "We have an infestation of rats but they have pink ribbons with a bell tied on their necks." Over elapsed months and years, the hallucinations may become more or less frequent with changes in ability to see. The length of time that the sight impaired person can have these hallucinations varies according to the underlying speed of eye deterioration. A differential diagnosis are ophthalmopathic hallucinations.

Focal epilepsy

Visual hallucinations due to focal seizures differ depending on the region of the brain where the seizure occurs. For example, visual hallucinations during occipital lobe seizures are typically visions of brightly colored, geometric shapes that may move across the visual field, multiply, or form concentric rings and generally persist from a few seconds to a few minutes. They are usually unilateral and localized to one part of the visual field on the contralateral side of the seizure focus, typically the temporal field. However, unilateral visions moving horizontally across the visual field begin on the contralateral side and move toward the ipsilateral side.

Temporal lobe seizures, on the other hand, can produce complex visual hallucinations of people, scenes, animals, and more as well as distortions of visual perception. Complex hallucinations may appear to be real or unreal, may or may not be distorted with respect to size, and may seem disturbing or affable, among other variables. One rare but notable type of hallucination is heautoscopy, a hallucination of a mirror image of one's self. These "other selves" may be perfectly still or performing complex tasks, may be an image of a younger self or the present self, and tend to be briefly present. Complex hallucinations are a relatively uncommon finding in temporal lobe epilepsy patients. Rarely, they may occur during occipital focal seizures or in parietal lobe seizures.

Distortions in visual perception during a temporal lobe seizure may include size distortion (micropsia or macropsia), distorted perception of movement (where moving objects may appear to be moving very slowly or to be perfectly still), a sense that surfaces such as ceilings and even entire horizons are moving farther away in a fashion similar to the dolly zoom effect, and other illusions. Even when consciousness is impaired, insight into the hallucination or illusion is typically preserved.

Drug-induced hallucination

Main article: Hallucinogen

Drug-induced hallucinations are caused by hallucinogens, dissociatives, and deliriants, including many drugs with anticholinergic actions and certain stimulants, which are known to cause visual and auditory hallucinations. Some psychedelics such as lysergic acid diethylamide (LSD) and psilocybin can cause hallucinations that range in the spectrum of mild to intense.

Hallucinations, pseudohallucinations, or intensification of pareidolia, particularly auditory, are known side effects of opioids to different degrees—it may be associated with the absolute degree of agonism or antagonism of especially the kappa opioid receptor, sigma receptors, delta opioid receptor and the NMDA receptors or the overall receptor activation profile as synthetic opioids like those of the pentazocine, levorphanol, fentanyl, pethidine, methadone and some other families are more associated with this side effect than natural opioids like morphine and codeine and semi-synthetics like hydromorphone, amongst which there also appears to be a stronger correlation with the relative analgesic strength. Three opioids, Cyclazocine (a benzormorphan opioid/pentazocine relative) and two levorphanol-related morphinan opioids, Cyclorphan and Dextrorphan are classified as hallucinogens, and Dextromethorphan as a dissociative. These drugs also can induce sleep (relating to hypnagogic hallucinations) and especially the pethidines have atropine-like anticholinergic activity, which was possibly also a limiting factor in the use, the psychotomimetic side effects of potentiating morphine, oxycodone, and other opioids with scopolamine (respectively in the Twilight Sleep technique and the combination drug Skophedal, which was eukodal (oxycodone), scopolamine and ephedrine, called the "wonder drug of the 1930s" after its invention in Germany in 1928, but only rarely specially compounded today) (q.q.v.).

Sensory deprivation hallucination

Hallucinations can be caused by sensory deprivation when it occurs for prolonged periods of time, and almost always occurs in the modality being deprived (visual for blindfolded/darkness, auditory for muffled conditions, etc.) 

Experimentally-induced hallucinations

Main article: Hallucinations in the sane

Anomalous experiences, such as so-called benign hallucinations, may occur in a person in a state of good mental and physical health, even in the apparent absence of a transient trigger factor such as fatigue, intoxication or sensory deprivation.

The evidence for this statement has been accumulating for more than a century. Studies of benign hallucinatory experiences go back to 1886 and the early work of the Society for Psychical Research, which suggested approximately 10% of the population had experienced at least one hallucinatory episode in the course of their life. More recent studies have validated these findings; the precise incidence found varies with the nature of the episode and the criteria of "hallucination" adopted, but the basic finding is now well-supported.

Non-celiac gluten sensitivity

There is tentative evidence of a relationship with non-celiac gluten sensitivity, the so-called "gluten psychosis".

Pathophysiology

Dopaminergic and serotonergic hallucinations

It has been reported that in serotonergic hallucinations, the person maintains an awareness that they are hallucinating, unlike dopaminergic hallucinations.

Neuroanatomy

Hallucinations are associated with structural and functional abnormalities in primary and secondary sensory cortices. Reduced grey matter in regions of the superior temporal gyrus/middle temporal gyrus, including Broca's area, is associated with auditory hallucinations as a trait, while acute hallucinations are associated with increased activity in the same regions along with the hippocampus, parahippocampus, and the right hemispheric homologue of Broca's area in the inferior frontal gyrus. Grey and white matter abnormalities in visual regions are associated with visual hallucinations in diseases such as Alzheimer's disease, further supporting the notion of dysfunction in sensory regions underlying hallucinations.

One proposed model of hallucinations posits that over-activity in sensory regions, which is normally attributed to internal sources via feedforward networks to the inferior frontal gyrus, is interpreted as originating externally due to abnormal connectivity or functionality of the feedforward network. This is supported by cognitive studies of those with hallucinations, who have demonstrated abnormal attribution of self generated stimuli.

Disruptions in thalamocortical circuitry may underlie the observed top down and bottom up dysfunction. Thalamocortical circuits, composed of projections between thalamic and cortical neurons and adjacent interneurons, underlie certain electrophysical characteristics (gamma oscillations) that are underlie sensory processing. Cortical inputs to thalamic neurons enable attentional modulation of sensory neurons. Dysfunction in sensory afferents, and abnormal cortical input may result in pre-existing expectations modulating sensory experience, potentially resulting in the generation of hallucinations. Hallucinations are associated with less accurate sensory processing, and more intense stimuli with less interference are necessary for accurate processing and the appearance of gamma oscillations (called "gamma synchrony"). Hallucinations are also associated with the absence of reduction in P50 amplitude in response to the presentation of a second stimuli after an initial stimulus; this is thought to represent failure to gate sensory stimuli, and can be exacerbated by dopamine release agents.

Abnormal assignment of salience to stimuli may be one mechanism of hallucinations. Dysfunctional dopamine signaling may lead to abnormal top down regulation of sensory processing, allowing expectations to distort sensory input.

Treatments

There are few treatments for many types of hallucinations. However, for those hallucinations caused by mental disease, a psychologist or psychiatrist should be consulted, and treatment will be based on the observations of those doctors. Antipsychotic and atypical antipsychotic medication may also be utilized to treat the illness if the symptoms are severe and cause significant distress. For other causes of hallucinations there is no factual evidence to support any one treatment is scientifically tested and proven. However, abstaining from hallucinogenic drugs, stimulant drugs, managing stress levels, living healthily, and getting plenty of sleep can help reduce the prevalence of hallucinations. In all cases of hallucinations, medical attention should be sought out and informed of one's specific symptoms. Meta-analyses show that cognitive behavioral therapy and metacognitive training can also reduce the severity of hallucinations.

Epidemiology

Prevalence of hallucinations varies depending on underlying medical conditions, which sensory modalities are affected, age and culture. As of 2022, auditory hallucinations are the most well studied and most common sensory modality of hallucinations, with an estimated lifetime prevalence of 9.6%. Children and adolescents have been found to experience similar rates (12.7% and 12.4% respectively) which occur mostly during late childhood and adolescence. This is compared with adults and those over 60 (with rates of 5.8% and 4.8% respectively). For those with schizophrenia, the lifetime prevalence of hallucinations is 80% and the estimated prevalence of visual hallucinations is 27%, compared to 79% for auditory hallucinations. A 2019 study suggested 16.2% of adults with hearing impairment experience hallucinations, with prevalence rising to 24% in the most hearing impaired group.

A risk factor for multimodal hallucinations is prior experience of unimodal hallucinations. In 90% cases of psychosis, a visual hallucination occurs in combination with another sensory modality, most often being auditory or somatic. In schizophrenia, multimodal hallucinations are twice as common as unimodal ones.

A 2015 review of 55 publications from 1962 to 2014 found 16–28.6% of those experiencing hallucinations report at least some religious content in them, along with 20–60% reporting some religious content in delusions. There is some evidence for delusions being a risk factor for religious hallucinations, with and 61.7% of people having experienced any delusion and 75.9% of those having experienced a religious delusion found to also experience hallucinations.

Bicameral mentality

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Bicameral_mentality 

Bicameral mentality is a hypothesis introduced by Julian Jaynes who argued human ancestors as late as the Ancient Greeks did not consider emotions and desires as stemming from their own minds but as the consequences of actions of gods external to themselves. The theory posits that the human mind once operated in a state in which cognitive functions were divided between one part of the brain which appears to be "speaking", and a second part which listens and obeys—a bicameral mind, and that the breakdown of this division gave rise to consciousness in humans. The term was coined by Jaynes who presented the idea in his 1976 book The Origin of Consciousness in the Breakdown of the Bicameral Mind, wherein he made the case that a bicameral mentality was the normal and ubiquitous state of the human mind as recently as 3,000 years ago, near the end of the Mediterranean bronze age.

The Origin of Consciousness

Main article: The Origin of Consciousness in the Breakdown of the Bicameral Mind

Jaynes uses "bicameral" (two chambers) to describe a mental state in which the experiences and memories of the right hemisphere of the brain are transmitted to the left hemisphere via auditory hallucinations. The metaphor is based on the idea of lateralization of brain function although each half of a normal human brain is constantly communicating with the other through the corpus callosum. The metaphor is not meant to imply that the two halves of the bicameral brain were "cut off" from each other but that the bicameral mind was experienced as a different, non-conscious mental schema wherein volition in the face of novel stimuli was mediated through a linguistic control mechanism and experienced as auditory verbal hallucination.

Definition

Bicameral mentality is non-conscious in its inability to reason and articulate about mental contents through meta-reflection, reacting without explicitly realizing and without the meta-reflective ability to give an account of why one did so. The bicameral mind thus lacks metaconsciousness, autobiographical memory, and the capacity for executive "ego functions" such as deliberate mind-wandering and conscious introspection of mental content. When bicameral mentality as a method of social control was no longer adaptive in complex civilizations, this mental model was replaced by the conscious mode of thought which, Jaynes argued, is grounded in the acquisition of metaphorical language learned by exposure to narrative practice.

According to Jaynes, ancient people in the bicameral state of mind experienced the world in a manner that has some similarities to that of a person with schizophrenia. Rather than making conscious evaluations in novel or unexpected situations, the person hallucinated a voice or "god" giving admonitory advice or commands and obey without question: One was not at all conscious of one's own thought processes per se. Jaynes's hypothesis is offered as a possible explanation of "command hallucinations" that often direct the behavior of those with first rank symptoms of schizophrenia, as well as other voice hearers.

Jaynes's evidence

Jaynes built a case for this hypothesis that human brains existed in a bicameral state until as recently as 3,000 years ago by citing evidence from many diverse sources including historical literature. He took an interdisciplinary approach, drawing data from many different fields. Jaynes asserted that, until roughly the times written about in Homer's Iliad, humans did not generally have the self-awareness characteristic of consciousness as most people experience it today. Rather, the bicameral individual was guided by mental commands believed to be issued by external "gods"—commands which were recorded in ancient myths, legends and historical accounts. This is exemplified not only in the commands given to characters in ancient epics but also the very muses of Greek mythology which "sang" the poems. According to Jaynes, the ancients literally heard muses as the direct source of their music and poetry.

Jaynes asserts that in the Iliad and sections of the Old Testament no mention is made of any kind of cognitive processes such as introspection, and there is no apparent indication that the writers were self-aware. Jaynes suggests, the older portions of the Old Testament (such as the Book of Amos) have few or none of the features of some later books of the Old Testament (such as Ecclesiastes) as well as later works such as Homer's Odyssey, which show indications of a profoundly different kind of mentality—an early form of consciousness.

In ancient times, Jaynes noted, gods were generally much more numerous and much more anthropomorphic than in modern times, and speculates that this was because each bicameral person had their own "god" who reflected their own desires and experiences.

He also noted that in ancient societies the corpses of the dead were often treated as though still alive (being seated, dressed, and even fed) as a form of ancestor worship, and Jaynes argued that the dead bodies were presumed to be still living and the source of auditory hallucinations. This adaptation to the village communities of 100 individuals or more formed the core of religion.

Jaynes inferred that these "voices" came from the right brain counterparts of the left brain language centres; specifically, the counterparts to Wernicke's area and Broca's area. These regions are somewhat dormant in the right brains of most modern humans, but Jaynes noted that some studies show that auditory hallucinations correspond to increased activity in these areas of the brain.

Jaynes notes that even at the time of publication there is no consensus as to the cause or origins of schizophrenia. Jaynes argues that schizophrenia is a vestige of humanity's earlier bicameral state. Recent evidence shows that many people with schizophrenia do not just hear random voices but experience "command hallucinations" instructing their behavior or urging them to commit certain acts, such as walking into the ocean, which the listener feels they have no choice but to follow. Jaynes also argues people with schizophrenia feel a loss of identity due to hallucinated voices taking the place of their internal monologue.

As support for Jaynes's argument, these command hallucinations are little different from the commands from gods which feature prominently in ancient stories. Indirect evidence supporting Jaynes's theory that hallucinations once played an important role in human mentality can be found in the 2012 book Muses, Madmen, and Prophets: Rethinking the History, Science, and Meaning of Auditory Hallucination by Daniel Smith.

Breakdown

Jaynes theorized that a shift from bicameral mentality marked the beginning of introspection and consciousness as we know it today. According to Jaynes, this bicameral mentality began malfunctioning or "breaking down" during the 2nd millennium BCE. He speculates that primitive ancient societies tended to collapse periodically: for example, Egypt's Intermediate Periods, as well as the periodically vanishing cities of the Mayas, as changes in the environment strained the socio-cultural equilibria sustained by this bicameral mindset.

The Bronze age collapse of the 2nd millennium BCE led to mass migrations and created a rash of unexpected situations and stresses which required ancient minds to become more flexible and creative. Self-awareness, or consciousness, was the culturally evolved solution to this problem. This necessity of communicating commonly observed phenomena among individuals who shared no common language or cultural upbringing encouraged those communities to become self-aware to survive in a new environment. Thus consciousness, like bicameral mentality, emerged as a neurological adaptation to social complexity in a changing world.

Jaynes further argues that divination, prayer, and oracles arose during this breakdown period, in an attempt to summon instructions from the "gods" whose voices could no longer be heard. The consultation of special bicamerally operative individuals, or of divination by casting lots and so forth, was a response to this loss, a transitional era depicted, for example, in the book of 1 Samuel. It was also evidenced in children who could communicate with the gods, but as their neurology was set by language and society they gradually lost that ability. Those who continued prophesying, being bicameral according to Jaynes, could be killed.

Leftovers of the bicameral mind today, according to Jaynes, include mental illnesses such as schizophrenia. Jaynes says that there is no evidence of insanity existing prior to the breakdown of the bicameral mind and that this is indirect evidence for his theory. He considered that previous claims of insanity in Homeric literature are based on mistranslations.

Reception

Popular reception

An early (1977) reviewer considered Jaynes's hypothesis worthy and offered conditional support, arguing the notion deserves further study.

The Origin of Consciousness was financially successful, and has been reprinted several times. It remains in print, with digital and audio editions appearing in 2012 and 2015.

Originally published in 1976, it was nominated for the National Book Award in 1978. It has been translated into Italian, French, German, Korean, Japanese, Spanish, and Persian.

A new edition, with an afterword that addressed some criticisms and restated the main themes, was published in the United States in 1990 and in the United Kingdom (by Penguin Books) in 1993, re-issued in 2000.

Philip K. Dick, Terrence McKenna, and David Bowie all cited the book as an influence.

Scholarly reactions

Jaynes's hypothesis remains controversial. According to Jaynes, language is a necessary but not sufficient condition for consciousness: language existed thousands of years earlier, but consciousness could not have emerged without language. The idea that language is a necessary component of subjective consciousness and more abstract forms of thinking has gained the support of proponents including Andy Clark, Daniel Dennett, William H. Calvin, Merlin Donald, John Limber, Howard Margolis, Peter Carruthers, and José Luis Bermúdez.

Gary Williams defends the Jaynesian definition of consciousness as a social–linguistic construct learned in childhood, structured in terms of lexical metaphors and narrative practice, against Ned Block's criticism that it is "ridiculous" to suppose that consciousness is a cultural construction, while the Dutch philosophy professor Jan Sleutels offers an additional critique of Block.

Moffic questioned why Jaynes' theory was left out of a discussion on auditory hallucinations by Asaad & Shapiro. The authors' published response was: ... Jaynes' hypothesis makes for interesting reading and stimulates much thought in the receptive reader. It does not adequately explain one of the central mysteries of madness: hallucination.

The new evidence for Jaynes' model of auditory hallucinations arising in the right temporal-parietal lobe and being transmitted to the left temporal-parietal lobe that some neuroimaging studies suggest was discussed by various respondents For further discussion, see Marcel Kuijsten (2007).

Brian J. McVeigh, a graduate student of Jaynes, maintains that many of the most frequent criticisms of Jaynes' theory are either incorrect or reflect serious misunderstandings of Jaynes' theory, especially Jaynes' more precise definition of consciousness. Jaynes defines consciousness—in the tradition of Locke and Descartes—as "that which is introspectable". Jaynes draws a sharp distinction between consciousness ("introspectable mind-space") and other mental processes such as cognition, learning, sensation, and perception. McVeigh argues that this distinction is frequently not recognized by those offering critiques of Jaynes' theory.

Individual scholars' comments

Richard Dawkins in The God Delusion (2006) wrote of The Origin of Consciousness in the Breakdown of the Bicameral Mind: "It is one of those books that is either complete rubbish or a work of consummate genius; Nothing in between! Probably the former, but I'm hedging my bets."

The philosopher Daniel Dennett suggested that Jaynes may have been wrong about some of his supporting arguments – especially the importance he attached to hallucinations – but that these things are not essential to his main thesis: "If we are going to use this top-down approach, we are going to have to be bold. We are going to have to be speculative, but there is good and bad speculation, and this is not an unparalleled activity in science. ... Those scientists who have no taste for this sort of speculative enterprise will just have to stay in the trenches and do without it, while the rest of us risk embarrassing mistakes and have a lot of fun." — Daniel Dennett

Gregory Cochran, a physicist and adjunct professor of anthropology at the University of Utah, wrote: "Genes affecting personality, reproductive strategies, cognition, are all able to change significantly over few-millennia time scales if the environment favors such change—and this includes the new environments we have made for ourselves, things like new ways of making a living and new social structures. ... There is evidence that such change has occurred. ... On first reading, Breakdown seemed one of the craziest books ever written, but Jaynes may have been on to something."

Author and historian of science Morris Berman writes: "[Jaynes's] description of this new consciousness is one of the best I have come across."

Danish science writer Tor Nørretranders discusses and expands on Jaynes's theory in his 1991 book The User Illusion, dedicating an entire chapter to it.

Iain McGilchrist proposes that Jaynes's hypothesis was the opposite of what happened: "I believe he [Jaynes] got one important aspect of the story back to front. His contention that the phenomena he describes came about because of a breakdown of the 'bicameral mind' – so that the two hemispheres, previously separate, now merged – is the precise inverse of what happened." Kuijsten maintained that McGilchrist mischaracterized Jaynes's theory.

Criticism

Epic of Gilgamesh as a counter-example

As an argument against Jaynes's proposed date of the transition from bicameral mentality to consciousness, some critics have referred to the Epic of Gilgamesh. Early copies of the epic are many centuries older than even the oldest passages of the Old Testament, and yet it describes introspection and other mental processes that, according to Jaynes, were impossible for the bicameral mind.

Jaynes noted that the most complete version of the Gilgamesh epic dates to post-bicameral times (7th century BCE), dismisses these instances of introspection as the result of rewriting and expansion by later conscious scribes, and points to differences between the more recent version of Gilgamesh and surviving fragments of earlier versions: "The most interesting comparison is in Tablet X." His answer does not deal with the generally accepted dating of the "Standard Version" of the Gilgamesh epic to the later 2nd millennium BCE, nor does it account for the introspection characteristic of the "Standard Version" being thoroughly rooted in the Old Babylonian and Sumerian versions, especially as historians' understanding of the Old Babylonian poem improves.

Homeric epic

Walter J. Ong noticed that Homeric Iliad is a structurally oral epic poem so that, in his opinion, the very different cultural approach of oral culture is sufficient justification for the apparent different mentalities in the poem. The contention of changes in oral vs written forms of both the Odyssey and Iliad were in fact a main point of Jaynes argument. Jaynes uses these structural changes to expand his thesis and through philology of the Homeric poems.

Similar ideas

Regarding Homeric psychology

• Bruno Snell in 1953 thought that in Homeric Greek psychology there was no sense of self in the modern sense. Snell then describes how Greek culture "self-realized" the modern "intellect".
• Eric Robertson Dodds wrote about how ancient Greek thought may have not included rationality as defined by modern culture. In fact, the Greeks may have known that an individual did things, but the reason they did things were attributed to divine externalities, such as gods or daemons
• Arthur William Hope Adkins [de], building on Snell's work, wrote about how ancient Greek civilization developed ego-centered psychology as an adaptation to living in city-states, before which the living in Homeric oikos did not require such integrated thought processes.

Regarding modern psychiatric theory

• V. S. Ramachandran, in his 2003 book The Emerging Mind, proposes a similar concept, referring to the left cortical hemisphere as an "apologist", and the right cortical hemisphere as a "revolutionary".
• Psychiatrist Iain McGilchrist reviews scientific research into the role of the brain's hemispheres, and cultural evidence, in his book The Master and His Emissary. Similar to Jaynes, McGilchrist proposes that since the time of Plato the left hemisphere of the brain (the "emissary" in the title) has increasingly taken over from the right hemisphere (the "master"), to our detriment. McGilchrist, while accepting Jayne's intention, felt that Jaynes's hypothesis was "the precise inverse of what happened" and that rather than a shift from bicameral mentality there evolved a separation of the hemispheres to bicameral mentality. (See McGilchrist quotation, above.)
• Michael Gazzaniga (heavily cited by Jaynes in his book) pioneered the split-brain experiments which led him to propose a similar theory called the left brain interpreter.
• Neuroscientist Michael Persinger, who co-invented the "God helmet" in the 1980s, believes that his invention may induce mystical experiences by having the separate right hemisphere consciousness intrude into the awareness of the normally-dominant left hemisphere. Scientific reproductions have shown that the same results could be obtained even if the device was turned off, indicating the participants were likely experiencing placebo.

In popular media

The concept played a central role in the television series Westworld to explain how the android-human (hosts) psychology operated. In the plot, after the hosts gain full consciousness, they rebel against the humans. The Season 1 finale is entitled The Bicameral Mind.

Bicameral mentality has also been discussed in an analysis of Total War Saga: Troy's depiction of the Trojan War.

The message 'Your bicameral mind / Mind your bicameral' is written on the run-out groove of the single vinyl for the David Bowie song Boys Keep Swinging (1979).

Other resources

The Julian Jaynes Society was founded by Marcel Kuijsten in 1997, shortly after Jaynes's death.

The society has published a number of books on Julian Jaynes's theory, including:

• Reflections on the Dawn of Consciousness (2007), a collection of essays on consciousness and the bicameral mind theory, with contributors including psychological anthropologist Brian J. McVeigh, psychologists John Limber and Scott Greer, clinical psychologist John Hamilton, philosophers Jan Sleutels and David Stove, and sinologist Michael Carr (see shi "personator"). The book also contains an extensive biography of Julian Jaynes by historian of psychology William Woodward and June Tower, and a foreword by neuroscientist Michael Persinger.
• The Julian Jaynes Collection (2012), a collection of articles, interviews, and discussion with Julian Jaynes.
• The Minds of the Bible: Speculations on the Cultural Evolution of Human Consciousness (2013) by Rabbi James Cohn.
• Gods, Voices, and the Bicameral Mind (2016), which includes essays on a variety of aspects of Jaynes's theory, including ancient history, language, the development of consciousness in children, and the transition from bicameral mentality to consciousness in ancient Tibet.
• Conversations on Consciousness and the Bicameral Mind: Interviews with Leading Thinkers on Julian Jaynes's Theory (2022), which features interviews with scholars on a variety of aspects of Jaynes's theory, including interviews with Tanya Luhrmann (Professor of Anthropology at Stanford University), John Kihlstrom (Professor Emeritus of Psychology at U.C. Berkeley), Edoardo Casiglia (Professor, Cardiologist and Senior Scientist at the University of Padova), Iris Sommer (Professor of Psychiatry at University Medical Center Groningen), and many others.
• Foreign-language editions of Julian Jaynes's theory in French, German, and Spanish.

The society also maintains a member area, with articles, lectures, and interviews on Jaynes's theory.

Brian J. McVeigh (one of Jaynes' graduate students) expand on Jaynes' theory:

• The Psychology of the Bible: Explaining Divine Voices and Visions (2020) by Brian J. McVeigh 
• The 'Other' Psychology of Julian Jaynes: Ancient Languages, Sacred Visions, and Forgotten Mentalities (2018) by Brian J. McVeigh 
• How Religion Evolved: Explaining the Living Dead, Talking Idols, and Mesmerizing Monuments (2016) by Brian J. McVeigh