Disconnection Syndromes: Consciousness, Behavior, and Functional Neuroanatomy
Disconnection Syndromes: Consciousness, Behavior, and Functional Neuroanatomy (Updated and Reprinted from Neuropsychiatry, Neuropsychology, Clinical Neuroscience, 3rd Edition
(Academic Press, 2000)
by Rhawn Joseph, Ph.D.

Disconnection Syndromes: Consciousness, Behavior, and Functional Neuroanatomy
Rhawn Joseph, Ph.D.


As the brain consists of numerous feature detectors, and as the brain and mind can entertain and contemplate multiple contents simultaneously, the contents of consciousness can coalesce forming multi-modal imagery. However, it is also possible to keep certain thoughts separate, and to keep certain contents distinct. That is, it is possible to maintain and generate separate streams of consciousness.

Consciousness, therefore, may be fractionated, such that one aspect of consciousness may reflect upon the stimuli which has provoked yet another aspect of consciousness. That is, the consciousness associated with one region of the neocortex may reflect upon the contents which has provoked the conscious activation of yet another region of the neocortex (Barbur et al., 1993; Joseph, 1986ab, 1988b; Sperry, 1984; Zeki, 1997), just as one might become conscious of a sliver of wood that has become inserted beneath a finger nail.

I contemplate the "key" I hold in my hand. The sensations are transmitted to the primary sensory receiving areas in the parietal lobe (Brodmann's 3,1,2). The primary receiving areas are incapable of recognizing the tactile sensations as "key." Yet, they become active while holding the key, and other regions of the neocortex may be alerted to this activity, and thus become conscious of it--such as the frontal lobe (Joseph, 1999a). This tactile information is next transmitted to the secondary receiving area (Brodmann's area 5) which combines these sensations, e.g., hard, serrated, small. The secondary somesthetic receiving areas however, cannot identify these sensations as being indicative of a "key,"--though again the frontal lobes may be well aware of this neocortical activity and in fact has the capacity to prevent further processing or to promote the transfer of this data to other regions of the brain (Joseph, 1999a). This information may then transmitted to the parietal somesthetic association areas. Here this information is integrated, assimilated and recognized, non-verbally, non-visually, as a "key."

The parietal association may also demonstrate the use of the key, although it cannot name or visualize it as this tissue does not possess the neurons which supplies auditory-visual information. And it may demonstrate the use of the key, although other regions of the brain do not yet know, and are not yet conscious of what it is being held in the patient's hand--as demonstrated in cases of brain injury, i.e. disconnection syndromes (Geschwind, 1965) including the splitting apart of the two hemispheres of the brain. The disconnected aspect of consciousness may act independently.

Consciousness can be fragmented in the sense that the area of the brain that receives direct input regarding the key may know it holds a key, and can demonstrate the use of the key, even though the rest of the brain cannot visualize the key or name it--a condition referred to as agnosia. Agnosia is secondary to a lesion disconnecting the parietal lobe from the IPL and superior temporal lobe, such that the language areas cannot gain access to this tactile information. However, in the non-damage brain, even before the information regarding the key is verbalized or visualized, tissues such as the frontal lobe are aware of this parietal-activity and are conscious of it.

Once this information is transmitted to the IPL, however, not only can the use of the key be demonstrated, but it may be named and visualized, with various regions of the neocortex supplying the verbal components and other areas supplying the visual, and so on (Joseph, 1982, 1986a). Tactile consciousness becomes a tactile-verbal-visual consciousness at the level of the IPL and the individual can visualized and name the key as well as describe its use.

Because the mind is modular, and hierarchical, vertical, and laterally organized and so on, and as different regions of the brain are specialized to perform specific functions, those aspects of consciousness associated with the neocortex, for example, may be unable to gain complete access to yet other areas and may be prevented from becoming conscious of the activity occurring in other regions of the brain (Dimond, 1980; Dimond & Beaumont, 1974; Dimond et al. 1972; Galin, 1974; Geschwind, 1965; Joseph, 1982, 1988a, 1992b; Joseph et al. 1984; Marzi, 1986; Myers, 1959; Hoppe, 1977). The neocortex of one half of the brain, may in fact, be unable to gain access to information occurring or even memories stored in the other half (Bures & Buresova 1960; Doty & Overman 1977; Hasegawa et al., 1998; Kucharski et al. 1990; Levy, 1974; Risse & Gazzaniga, 1979), such that the information it receives may be incomplete, distorted, riddled with gaps, etc., such that this information becomes misinterpreted. In cases of brain injury, the consciousness associated with one half of the brain may become isolated and unable to gain access even to information within the same hemisphere, and that fractured aspect of mind may act independently; that is, with a mind of its own (Geschwind, 1965; Joseph, 1986a, 1988a). Conscious awareness is modular, hierarchical, lateralized, parallel, distributed, localized, and is thus subject to fracture. FUNCTIONAL DISCONNECTIONS AND THE SPLITTING OF CONSCIOUS-AWARENESS

Because the left hemisphere is not always able to fully comprehend the messages and signals that are processed by the right (and vice versa), and as it is also dominant for language and motor control, it will sometimes interfere with and attempt to inhibit and suppress the expression of what it does not understand (Levy, 1974; Joseph, 1988ab). That is, it will attempt to interfere with the right hemisphere even when the right is responding correctly or intelligently.

Consider, for example, a split-brain patient, "2-C" who demonstrated two disconnected forms of conscious awareness which acted independently and which were often in conflict (see below). In the laboratory the verbal portions of "2-C" mind would express anger about the independent tendencies of the left half of his body. He struck it with his right hand and expressed hate for it. Moreover, the right hand even attempted to prevent the left hand from following the directions and acting according to the instructions given to both halves of his brain (and mind) by this examiner (Joseph, 1988b). On one task, both hands were stimulated simultaneously (while out of view) with either the same or two different textured materials (e.g., sandpaper to the right, velvet to the left). "2-C" was required to point (with the left and right hands simultaneously) to the correct fabric by pointing to an array of fabrics hanging in view on the left and right of the testing apparatus. Although his left hand (right hemisphere) repeatedly responded correctly, his left hemisphere disagreed and vocalized: "Thats wrong!" as it apparently believed the fabric that had been rubbed on the right hand was also rubbed on the left. Repeatedly his right hand tried to force his left hand to point to the fabric experienced by the right. His left hand (right hemisphere) refused as it not only correctly perceived the tactile-stimulus, but remembered it and pointed to it, and physically resisted being forced to point at anything different. In one instance a physical struggle ensued, the right grappling with and slugging the left which then fought back.

Even among those who have never undergone "split-brain surgery" the left hemisphere may attempt to suppress the right (Hoppe, 1977; Galin, 1974). Moreover, because the left hemisphere relies on logic as well as language, it may logically explain away the feelings and other mental processes generated within the right half of the brain. For example, some left hemispheres don't believe in "intuition" and are quick to disavow "gut feelings," "warning signs," "red flags," and "alarm bells" and so on. However, this is not always due to prejudice, but rather ignorance. The left hemisphere is socially and emotionally retarded and does not posses the neural capability to adequately and correctly perceive, discriminate, or recognize social emotional nuances (Blumstein & Cooper, 1974; DeUrso et al. 1986; Dwyer & Rinn, 1981; Heilman et al. 1975, 1984; Lalande et al. 1992; Starkstein et al. 1994) including humor or mirth (Gardner et al. 1975) or even oppositional emotional qualities, e.g., "sarcasm vs irony" or "love" vs "hate" (Cicone et al. 1980; Kaplan et al. 1990). In consequence, and as also demonstrated by Levy and Trevarthen (1978), the left hemisphere may actively attempt to suppress and inhibit the right hemisphere and ignore or refuse to take into consideration its contributions when confronted with various problems even when the right hemisphere is better adept at solving these problems.

Unfortunately, this can lead to unfortunate consequences, especially in matters of the heart.


Functional dissociations are perhaps a normal aspect of psychic existence, as different regions of the brain and mind subserve wholly different capabilities and essentially speak different languages. Moreover, psychic upheavals are not uncommon, such that the neocortically equipped rational and logical aspects of mind may be completely overwhelmed by limbic and emotional concerns, including, for example, extreme fear or sexual jealousy. Under emotionally traumatizing conditions, however, the brain and the mind may be injured and may literally fracture and break apart, giving rise to a host of disconnections syndromes and associated dissociative phenomenon.

Dissociative experience, according to DSM-IV (1994, p. 477), is due to "a disruption in the usually integrated functions of consciousness, memory, identity, or perceptions of the environment." Dissociative phenomenon are typically associated with severe emotional trauma (Janet, 1927) such as rape, physical assault, or catastrophe (Courtois, 1995; Terr, 1994; van der Kolk & Fisler 1995), as well as repeated instances of severe and profound childhood sexual abuse, sometimes involving sexual torture. Typically, dissociative experiences may include dreamy states, fragmentation of consciousness, paralytic fear, and traumatic amnesia, as well as sensations or hallucinations of floating beside or above the body.

Dissociative experiences have also been associated with hypnosis (Hilgard, 1977/1986; Janet, 1927; Kihlstrom, 1985), and has been reported among neurosurgery and epilepsy patients and those who have undergone corpus callosotomy or suffered neurological injury, Under these conditions patients may also experience amnesia, the splitting of consciousness, as well as out-of-body sensations and body image distortions such as the "alien hand" and loss of memory for the left half of the body.

Emotional trauma can induce neurological injury ( Lupien & McEwen, 1997, Sapolsky, 1996) and create functional disconnections syndromes and a splitting of consciousness. Hence, under both emotional and neurologically traumatic conditions, the ego and thus consciousness may fracture and split apart, such that a fragmentary (and traumatized) aspect of the ego and the brain (including associated ideas, perceptions, feelings, and memories) may come to be dissociated from the dominant stream of conscious activity (Janet, 1927; Joseph, 1998b, 1999b,d). According to Janet (1927), in response to overwhelming emotional stress, and because the ego and consciousness may be "fractured," the abiltity to control or bind together all aspects of the psyche and the mind is lost. In consequence, the traumatized, injured, and broken off aspects of the mind may also act independently as if under the control of a separate personality.

Janet (1927) has argued that these dissociated elements of the ego, under some conditions, can essentially take on a life of their own and may in fact independently develop and grow (see also Jung, 1964; regarding complexes). Nevertheless, because it has been dissociated and thus disconnected from this broken off aspect of the psyche, the dominant and verbal aspect of the personality and consciousness may be unaware that the broken off segment is acting independently. Identical disturbances have been documented following neurological injury including corpus callosotomy (Joseph, 1988a,b).

It is noteworthy that although Freud (1915; Breuer & Freud 1893) also repeatedly documented cases of dissociation, in which various aspects of the psyche could come to be split off from consciousness, he also believed that under traumatic conditions that it was the emotion or impulse associated with an idea (or memory) that came to be disconnected and dissociated; i.e. repressed. Thus the emotion or impulse and the associated memory disapear into the unconscious. According to Freud (1915), through this expulsion from consciousness, painful ideas, memories, impulses and feelings could come to be repressed and dissociated from the ego. Nevertheless, this dissociation is not always complete for repressed material and related ideas can seek entry or seep into consciousness in the form of fragmented images and "reminiscences" (Breuer & Freud, 1893) and thus achieve a partial conscious realization. Similar seepage has also been demonstrated with split-brain patients (Joseph, 1986b, 1988a,b).

Freud also believed that the various components of the mind were in fact naturally separated and thus fragmented; a theory which is also supported by evidence from neurology). Thus the ego was conscious as well as unconscious, and it was the unconscious realms into which rejected and dissociated impulses could be deposited. That is, the unacceptable impulse is either rejected by the conscious mind and/or it is denied entry into consciousness by the unconscious mind (via the unconscious censors) and is repressed. Freud thus downplayed the significance of dissociation and instead embraced and developed the concept of the "unconscious" and "repression" which essentially became the "cornerstone" of psychoanalysis (Freud 1900, 1915).

Although these two clinicians essentially championed major constructs that somewhat differed from that of the other (i.e. dissociation vs repression), and although Freud argued that repression may be triggered in response to unacceptable impulses, Janet (1927) and Freud (1896,1900,1905,1916,1931, 1937), were in basic agreement as to the role of emotional and psychic trauma as a primary cause of repression and dissociative states. That is, emotional trauma can create a condition where the experience and associated memories become disconnected and dissociated from the dominant stream of verbal consciousness and thus repressed. Again, however, the same exact symptoms can be produced following neurological injury, and this is because emotional trauma can injure as well as abnormally activated the brain, thereby giving rise to a dissociative amnesia, a splitting of consciousness, and a host of related disconnection symptoms including the sensation of floating outside the body.


The brain is organized such that four distinct, albeit overlapping mental systems, are essentially localized one on top (brainstem/limbic system) and one beside the other (right/left hemisphere). However, because the "mental systems" of the brain are hierarchically organized and lateralized, they are not always able to fully communicate as they speak different languages. Indeed, given the newly evolved ability to employ language and logic, and the fact that half of the brain is depending on language for understanding whereas older social-emotional mental systems are lateralized to the right half of the cerebrum, this lateralized system of mental activity often predisposes humans to developing intra-psychic conflicts and to sometimes ignore or suppress "warning signs" and "alarm bells" when interacting with others, members of the opposite sex and business and political opponents in particular. Often the left fails to attend to or acknowledge what the right hemisphere is fully aware of, a consequence of functional disconnection secondary to functional lateralization.

Functional disconnections may be induced by conflicting emotional concerns, and under conditions of tremendous emotional stress. However, in these latter instances, the brain may in fact be damaged (Lupien & McEwen, 1997; Sapolsky, 1996). And if the brain is damaged, then so too is the mind. As noted, conscious-awareness, including linguistic-consciousness is subject to fracture if the cerebrum is sufficiently stressed or physically injured. Under conditions of severe emotional stress, various aspects of the mind may in fact come to be extinguished and completely eclipsed. For example, victims become paralyzed with fear and there may be a complete cessation of mental activity, such that even memory is abolished. Moreover, associated structures, such as the hippocampus and amygdala may be injured thereby giving rise to long term disturbances of emotion and memory as well as the development of alternative personalities.

The brain and the mind can also become fractured and disconnected from yet other regions of the brain and mind due to head injury, stroke, tumor, or epilepsy. In some cases, the neocortex may be disconnected from limbic sources of input, the right hemisphere may be disconnected from the left hemisphere and the language dependent mind, and in some cases the language axis itself may be fractured such that Broca's area may be unable to communicate with Wernicke's area.

For example, if Broca's area is disconnected from Wernicke's area and the IPL due to a lesion of the arcuate fasciculus, the patient will suffer an extreme "tip of the tongue" word finding difficulty, and might completely lose the ability to produce speech altogether, though they still "know" what they wish to say; referred to as conduction aphasia, or in the less extreme, anomia (Goodglass & Kaplan 1999). However, in some instances the linguistic aspects of consciousness may remain intact, but become disconnected and thus dissociated from a non-verbal region of the mind (Bogen, 1993; Critchley, 1964; Freud, 1891; Geschwind, 1965; Joseph, 1986a,b, 1988a,b; Sperry, 1966, 1982). If that occurs, the disconnected aspect of non-verbal awareness may act independently of that portion of the mind associated with language and verbal thought.


In some instances of cerebral trauma, the language axis may become disconnected from yet another region of the brain that remains intact and which subserves a different aspect of consciousness. That is, conscious awareness may be split and fragmented. However, the broken off portions of consciousness may retain the ability to engage in complex actions as well as store these experiences in memory (Bogen, 1969, 1993; Geschwind, 1965; Joseph, 1986b, 1988b; Sperry, 1966, 1982). For example, if a patient suffers a discrete lesion in the left occipital-temporal visual associations areas, although vision is preserved and the patient can see (due to preservation of the primary visual cortex), they will be unable to verbally recognize, describe, or name objects that are shown to them, even if encouraged to guess or if provided multiple choices. This is because the language axis is disconnected from the visual association areas and cannot receive complex visual associations. It cannot name what it sees because it cannot match an auditory equivalent with the visual image due to disconnection. Instead, the language axis may confabulate and call a "glass of water" a "clock" or a "comb" a "harmonica" or "toothbrush," and so on, and they may fail to realize an error has been made (Freud, 1891; Geschwind, 1965). Although unable to name or identify a glass of water, or explain its function or utility, once they became thirsty they might pick up the glass and drink from it (Geschwind 1965). Nevertheless they may remain unable to name the item even during the course of utilizing it (depending on the extent of disconnection).

If instead the lesion disconnected the Language Axis from the left superior parietal lobule and the primary receiving areas for somasthesis, although able to correct name what they see, the patient would be unable to name whatever object might be secretly placed in their right hand, e.g. a "comb;" for example, if they were blindfolded, a condition referred to as stereoagnosia. In fact, they may not consciously (verbally) realize something was placed in their hand. They cannot name objects explored by touch alone because that aspect of consciousness associated with language is disconnected from that portion of consciousness that recognizes objects by touch. However, although unable to name, for example, a comb that had been placed in their hand, they can still demonstrate its use by combing their hair (Freud, 1891; Geschwind, 1965).

These unusual disturbances are not due to "word finding" difficulties for if provided multliple choices they may still fail to pick the right word (Geschwind 1965). The object cannot be verbally identified because the Language Axis and verbal-consciousness have been disconnected and thus dissociated from the area of perception; a result of a lesion that destroys the axonal interconnections that normally link these neocortical tissues. Hence, if provided the correct word or descriptive phrase; i.e. "Is it a comb or a toothbrush?" the patient may still chose the wrong word or confabulate (Joseph 1982, 1986ab, 1988ab). They are unable to match the word with the visual or somesthetic image due to disconnection.

As demonstrated above, the dissociated area of perception can sometimes continue to act in isolation and can maintain a fragmentary non-verbal awareness which "it" may act on independently (Geschwind 1965). That is, the disconnected brain area that has been isolated from the Language Axis, may respond "normally". Hence, if asked to draw the object, or to show how it is used, they can do so, even though consciously, they cannot verbally describe or recognize what the object is. Thus, under these conditions, that aspect of the mind and personality that drinks from the glass or demonstrates the use of a comb, represents a broken off and disconnected fragment of the "mind" that is no longer attached to the dominant verbal stream of consciousness. However, this broken-off fragment of consciousness remains fully capable of acting independently and in a purposeful and intelligent manner. As stated by Geschwind (1965), under these conditions "we are dealing with more than one patient. The patient that speaks to you is not the patient who is perceiving--they are, in fact separate."

It is noteworthy that some academics claim that there is no evidence that consciousness can be fragmented or split apart following a brain lesion or as a consequence of emotional trauma. Nevertheless, as should be evident, those who make those claims are woefully uninformed. Indeed, not only does emotional trauma induce dissociative abnormalities, but all forms of dissociation are directly related to neurological abnormalities. If the brain is injured it is not uncommon for different mental systems to become disconnected and to act independently, as is the case with blind sight, and following split-brain surgery or medial frontal injuries.


Following damage to the primary visual neocortex patients will become "blind" (cortically blind) and will be unable to see, name or describe complex visual stimuli, though they may perceive motion or gradations in lighting (Holmes, 1918; Scharli, Harman & Hogben, 1999; Weiskrantz, 1986, 1996). Although blind, these patients may avoid obstacles, and correctly retrieve desired objects, and thus appear to have some residual visual functions even though they verbally claim no conscious awareness of the visual stimulus and thus have no verbal awareness that they can see (Poppel, Held & Frost, 1973). Nevertheless, although the verbal aspects of consciousness have been disconnected from the visual cortex and claims it cannot see, the patient continues to behave as if visual input is still being received; hence the term "blind sight."

Specifically, those who are "cortically" blind but demonstrate "blind sight" accomplish these acts apparently because undamaged midbrain, thalamic, and neocortical tissues (e.g. temporal/parietal lobe) involved in visual functioning continue to function normally (Milner & Goodale, 1995; Stoerig, 1996; Ziki, 1997), although completely dissociated from the "dominant" stream of verbal consciousness mediated by the left hemisphere.

For example, although "cortically blind" the eyes are functional, and visual impressions are transmitted via the optic nerve directly to the midbrain visual colliculus, and via the optic tracts and optic radiations to the lateral geniculate nucleus of the thalamus and other forebrain structures including the visual areas in the temporal and parietal lobe (Milner & Goodale, 1995; Stoerig, 1996). In some cases, this residual visual input may be transmitted to those islands of striate cortex which remain intact (Wessinger et al., 1997). However, in other cases, there is no evidence for functional activity in the primary visual receiving areas as residual vision appears to be due to the preservation of a visual area located in the temporal occipital border and which responds to visual motion (Barbou, et al., 1993; Zeki, 1997); and/or the midbrain visual colliculus (see chapter 17).

Nevertheless, in cases of "blindi sight" these intact areas are unable to communicate with the language areas of the brain, which, in failing to receive visual signals, claims to have no knowledge of the visual world, other than "non-visual feelings" (Scharli, et al., 1999). However, although disconnected form the language axis, which reports only "non-visual feelings" these isolated visual areas may continue to mediate behavior, perhaps via connections with the midbrain--a structure which responds to visual motion, and which can direct head and orienting movements (Blessing, 1997, Klemm & Vertes, 1990)

Consider, for example, the classic cases of blindsight first described by Riddoch (1917). According to Riddoch (1917) although these patients had suffered extensive destruction of the primary visual areas, they remained "conscious of something moving when the object oscillate... and that.... the consciousness of something moving kept up a continual desire to turn the head."

The fact that these and other patients with blind sight may have a feeling of seeing movement (Scharli et al., 1999; Zeki, 1997), are/or experience a desire to turn the head (Riddoch, 1917), and/or correctly reach out and grasp or move around objects, directly implicates the midbrain visual colliculus as this structure is able to detect movement and different gradations of light and shadow (Davidson & Bender, 1991), and (via the lower brainstem) can direct head turning, groping and grasping, and even walking (Blessing, 1997; Klemm & Vertes, 1990).

For example, because the midbrain visual colliculus is able to detect movement and different gradations of light and shadow (Davidson & Bender, 1991), and (via the lower brainstem) can direct head turning, groping and grasping, and even walking (Blessing, 1997; Joseph, 1999c; Klemm & Vertes, 1990), this may explain why patients with blindsight can still motorically respond to visual stimuli. Indeed, one does not need language or a neocortex in order to perform complex movements, which is why creatures such as reptiles, frogs, etc., are capable of complex visually guided behaviors even though they never evolved language or neocortex.

Humans, however, have evolved neocortex, and the primary visual receiving areas hierarchically analyze these subcortical visual signals which are then transferred to the adjoining visual association areas thereby forming complex visual associations (Kaas & Krubitzer, 1991; Milner & Goodale, 1995; Sereno, Dale, & Reppas, 1995). These complex associations are then transmitted to the language axis which then names and verbally describes what the individual sees (Critchley, 1964; Geschwind, 1965; Joseph, 1982). These visual impressions come to be associated with language and thus with linguistic consciousness. However, with massive injuries to the primary visual cortex, the language axis no longer receives visual input, and the patient reports that he or she is blind and cannot see, though they avoid obstacles and can reach for desired objects and or report non-visual "feelings."

Thus patients with "blind sight" demonstrate at least two disconnected streams of mental activity, one of which utilizes language to deny visual experience other than through the experience of "feelings", and a second non-verbal form of subcortical or isolated neocortical mental activity that is capable of seeing and/or controlling movements of the body in response to certain visual stimuli. Moreover, these multiple modes of conscious-awareness, including those supporting blindsight may wax and wane, "resulting in blindsight in some test sessions and in conscious awareness of the same stimuli in others... which raises the interesting question of whether the brain switches from one neural system to another during the waxing and waning of consciousness (Zeki, 1997, p. 175).


In contrast to those who display blindsight, in some cases immediately following massive injury to the visual neocortex and the surrounding visual association areas, although cortically blind, patients may initially deny blindness (Redlich & Dorsey, 1945; Joseph, 1986a) --a condition referred to as Anton's syndrome. For example, a number of patients described by Redlich and Dorsey (1945), refused to acknowledge blindness, even when they bumped into furniture, tripped and fell to the floor, and were unable to describe or name objects shown to them. Rather, when told of their disability by doctors and family, they instead invented elaborate excuses for their errors; e.g. claiming that it is a little dark and they need their glasses, or conversely, that they see better at home. That is, these patients confabulate due to disconnection of the language axis and its propensity to fill the gaps in the information received with related ideations (Joseph, 1982, 1986a, 1988a,b).

Specifically, because all visual cortices including the association areas have been destroyed, the language axis is completely disconnected and receives absolutely no information regarding the visual status of the brain and cannot be informed that it no longer sees (Critchley, 1964; Geschwind, 1965). The intact (non-visual) portion of the brain does not know it is blind (due to the destruction of all neocortical visual areas), just as the brain of a creature that never evolved sight does not know that it cannot see--a condition also referred to agnosagnosia (not knowing that they do not know). Instead, the language area fills the gaps and discrepancies in the information available by confabulating an explanation as to why they cannot see, i.e. "I see better at home." By contrast, those who admit to blindness receive signals form the still intact visual association areas which inform the language axis that no visual signals are being received from the damaged primary visual cortex.


Dr: "Give me your left hand!" (The patient presents the right hand. The doctor takes hold of the right hand.)

Dr: "Give me your left hand!" (The patient looked puzzled and did not move.) Dr: "Is there anything wrong with your left hand?"
Pt: "No, doctor."
Dr. "Why don't you move it, then?" (The left hand was held before her eyes.)
Pt.: "I don't know."
Dr: "Is this your hand?"
Pt: "Not mine, doctor."
Dr: "Whose hand is it, then?"
Pt: "I supposed it's yours, doctor."
Dr: "No, it's not. I've already got two hands. Look at it carefully."
Pt. "It is not mine, doctor."
Dr: "Yes it is, look at that ring; whose ring is it?"
Pt.: "That's my ring; you've got my ring, doctor."
Dr: "Look at it--it is your hand.
Pt: "Oh, no doctor."
Dr: "Where is your left hand then?"
Pt: "Somewhere here, I think." (Making groping movements near her left shoulder.)

With massive destruction of the visual cortex, patients may deny blindness. However, with massive destruction of the right superior parietal lobe--a neocortical area which maintains a memory of the body image--patients may deny the existence of half their body (Bisiach, & Geminiani, 1991; Critchley, 1953; Heilman, 1993; Joseph, 1986a, 1988a; Sandifer, 1946).

The primary somatosensory areas receives somesthetic and proprioceptive stimuli (Kaas, 1993; Kaas, Nelson, Sur, & Merzenich, 1981). However, because the right parietal lobe maintains a bilateral memory-image of the body (whereas the left lobe maintains only a right sided-body image), if destroyed, all left-sided somatosensory memories may be abolished and the language axis will become amnesic for half the body (Joseph, 1986a); a condition also referred to as unilateral neglect and inattention (Bartolomeo et al., 1994; Binder et al. 1992; Bisiach et al., 1983; Bisiach, & Geminiani,1991; Heilman, 1993). These patients (i.e. the intact left hemisphere) will also fail to comb, wash, or dress the left half of their head, face, and body, and when shown their left arm or leg, they may claim that it belongs to the doctor or a patient in the next room. Indeed, "patients with severe unilateral neglect behave as if a whole system of beliefs have vanished, as if one half of the inner model of the environment were simply deleted from their mind (Bisiach et al., 1983, p. 35).


Because all memories of the left side of the body are abolished, the language axis may fill the gap in its knowledge by referring to their left side with ego-alien language, attributing its presence to relatives, a patient in the next room, or the doctor. For example, Gerstmann (1942) describes a patient who "did not realize and on being questioned denied, that she was paralyzed on the left side of the body, did not recognize her left limbs as her own, ignored them as if they did not exist, and entertained confabulatory and delusional ideas in regard to her left extremities. She said another person was in bed with her, a little Negro girl, whose arm had slipped into the patient's sleeve" (p. 894). Another declared, (speaking of her left limbs), "That's an old man. He stays in bed all the time."

Another patient engaged in peculiar erotic behavior with his left limbs which he believed belonged to a woman. A patient described by Bisiach and Berti (1987, p. 185) "would become perplexed and silent whenever the conversation touched upon the left half of his body; even attempts to evoke memories of it were unsuccessful." Moreover, although "acknowledging that all people have a right and a left side, he could not apply the notion to himself. He would affirm that a woman was lying on his left side; he would utter witty remarks about this and sometimes caress his left arm".

Some patients may develop a dislike for their left limbs, try to throw them away, become agitated when they are referred to, entertain persecutory delusions regarding them, and even complain of strangers sleeping in their beds (Bisiach & Berti, 1987; Critchley, 1953; Gerstmann, 1942). Likewise, the left hemisphere of some split-brain patients may verbally claim to hate the left half of their body and attribute to it disagreeable personality traits or claim that it has engaged in behavior which the speaking half of the brain finds unpleasant, strange, objectionable, embarrassing, or contrary to it's wishes (Joseph, 1988ab).

Moreover, just a the left hemisphere of some "split-brain" patients may view the left half of the body as being controlled by a separate personality, patients with massive right parietal lesions may react in a similar fashion when confronted with their left arms and legs. One woman who was confronted with her paralyzed left arm said it belonged to another person whom she thought was in bed with her. Another declared (speaking of her left limbs), "That's an old man. He stays in bed all the time."

One patient complained that this other person tried to push her out of the bed and threatened to sue the hospital. Another complained about "a hospital that makes people sleep together." Another patient, after bumping into her left arm and leg all night, bitterly complained about "a hospital that makes people sleep together." She expressed not only anger but concern least her husband should find out; she was convinced it was a man in her bed.

As discussed and detailed in chapter 10, the right hemisphere is dominant for the establishment of emotional and personal memories, including memories associated with the body image which are maintained in the right parietal lobe. Hence, with massive right parietal injuries all memories of the left half of the body are erased, resulting in a dissociative amnesia for half of the body.

Essentially, with massive right parietal lesions, the left hemisphere and language dependent aspects of consciousness aree denied access to all memories regarding the left half of the body which have been destroyed. In consequence, the left hemisphere may be unable to recognize or remember the left half of their body as all memories have been erased. The language axis of the intact left hemisphere, when confronted with the left half of their body, will experiences it as completely alien and as perhaps belonging to someone else, such as the examining physician. That is, the language axis may fill the gaps in its knowledge and available memories by making up explanations which it accepts as truth (Joseph, 1986a, 1988ab; Joseph et al., 1984). It conjures up false memories; confabulations which go uncorrected as all associated memories regarding the left half of the body have been erased from consciousness.


As is well known, the right versus the left hemisphere controls the left versus the right hand and subserves different aspects of conscious experience, e.g. emotion, visual spatial functioning, and non-verbal memory (Borod et al., 1992; Brewer et al., 1998; Cimino et al., 1991; Freeman & Traugott, 1993; Heilman & Bowers 1995; Joseph, 1988a,b), versus mathematical reasoning and the grammatical, verbal components of expressive/receptive speech and memory (Bastiaanse, 1995; Goodglass & Kaplan, 1999; Njemanze, 1991; Wagner et al., 1998). Unity in the stream of consciousness, including coordination of movement and goal directed activity, is made possible, in part, through a massive rope of axonal fibers, the medially located corpus callosum. The corpus callosum interconnects the right and left hemisphere and enables the two halves of the brain to share cognitions, memories, and coordinates goal directed motor activities. If the corpus callosum, or adjoining medially located tissues are injured, this unity will be fractured to varying degrees depending on the extent of the lesion.

For example, Goldberg (1987, p 290) described a 53 year old right-handed women, "B.D." who while at work was overcome with a "feeling of nausea and began to notice that her left leg felt 'as if it did not belong to me.' This feeling of being dissociated from her body spread to the rest of her left side. At home, her symptoms began to worsen." Subsequent CT scan and MRI indiciated an infarct to the medial frontal lobe and damage to the body of the corpus callosum. "While sleeping one night a few days after admission to the hospital, she woke up sudden and notice her own left hand scratching her shoulder.... She would frequently look down to find the hand doing something that she had no idea it had been doing. She found this very disturbing and was convinced that she was going crazy."

Another patient described by Goldberg (1987, p. 295) reported "an incident in which she was lying in bed with the window open when suddenly the impaired limb reached down and pulled up the covers, functioning entirely in the alien mode. She concluded that 'it' must have felt cold and needed to cover her up. She felt that frequently the 'alien' did things that were generally 'good for her.'"

McNabb, Caroll, and Mastaglia (1988, pp. 219, 221) describe a woman with extensive damage involving the medial left frontal lobe and anterior corpus callosum, whose right "hand showed an uncontrollable tendency to reach out and take hold of objects and then was unable to release them. At times the right hand interfered with tasks being performed by the left hand. She attempted to restrain it by wedging it between her legs or by holding or slapping it with her left hand. The patient would repeatedly express astonishment at these actions." When yet another patient was "attempting to write with her left hand, the right would reach over and take the pencil. The left hand would respond by grasping the right hand to restrain it."

A patient described by Gasquoine (1993) had a propensity to reach out with his right hand and touch female breasts. This caused him great embarrassment and he would typically take hold of his right with his left hand to restrain it.

Similar problems have plagued patients following complete (surgical) destruction of the corpus callosum. For example, Akelaitis (1945, p. 597) described a female "split-brain" patient who became quite depressed and irritated about the actions of the left half of her body. On several occasions it tried to slam a drawer on her right hand, and on a number of instances the left hand (right hemisphere) attempted to take her clothes off, even though that is not what she (i.e. the left hemisphere) desired to do. Another patient experienced difficulty while shopping, the right hand would place something in the cart and the left hand would put it right back again. A recently divorced male patient noted that on several occasions while walking about town he found himself forced to go in another direction by the left half of his body which insisted on leading him to the home of his ex-wife.

Bogen (1993) reports that almost all of his "complete commissurotomy patients manifested some degree of intermanual conflict in the early postoperative period." One patient, Rocky, experienced situations in which his hands were uncooperative; the right would button up a shirt and the left would undo the buttons. For years, he complained of difficulty getting his left leg to go in the direction he (or rather his left hemisphere) desired.

Geschwind (1981) reports a callosal patient who complained that his left hand on several occasions suddenly struck his wife--much to the embarrassment of his left (speaking) hemisphere. In another case, a patient's left hand attempted to choke the patient himself and had to be wrestled away.

A split-brain patient described by Dimond (1980, p. 434) reported that once when she had overslept her left hand began slapping her face until she (her left hemisphere) woke up. This same patient, in fact, complained of several instances where her left hand had acted violently. Another split brain individual's left hand would not allow the patient to smoke, and would pluck lit cigarettes from his mouth and put them out (Joseph, 1988a).

These independent activities are not limited to the hands or legs, for following corpus callosotomy the two cerebral hemispheres may demonstrate different attitudes, and will form separate memories and essentially demonstrate two separate and dissociated streams of consciousness.

For example, one "slit-brain" patient, following a break up with his girlfriend, was asked if he wanted to get back with her (Joseph, 1986b). Although he said "no," when asked to indicate with a thumbs up or down, his non-verbal hemisphere repeatedly gave a thumbs up. The left and right hemisphere of another split-brain patient ("2-C") enjoyed different foods and television shows. Once, after "2-C" retrieved something from the refrigerator, his left hand grabbed the food from his right hand, put it back on the shelf and retrieved a completely different item "Even though that's not what I wanted to eat!" his left (speaking) hemisphere complained. On at least one occasion, his left leg refused to continue "going for a walk" and would only allow him to return home.

Split brain surgery obviously produces two dissociated forms of consciousness. If tactually stimulated on the left side, the verbal portion of consciousness which resides in the left hemisphere, may fail to realize that the body has been touched, though it responds correctly if the right side of the body is stimulated. The left hemisphere fails to name objects placed in the left hand, and fails to verbally report the presence of a moving or stationary stimulus in the left (but not right) half of their visual field. It cannot verbally describe pictures or auditory stimuli tachistoscopically or dichotically presented to the right cerebrum, and it is often completely mystified when the left half of their body responds or behaves in a particular purposeful manner, such as when the right hemisphere is selectively given a command (Bogen, 1969, 1993; Joseph, 1988b; Levy, 1974, Sperry, 1966, 1982).

However, by raising their left hand (which is controlled by the right half of the cerebrum) the disconnected right hemisphere is able to indicate when it is tactually or visually stimulated on the left side. When tachistoscopically presented with words to the left of visual midline, although unable to name them, when offered mutiple visual choices the right hemisphere will point with the left hand to the correct item. Thus although disconnected from "verbal" consciousness, right cerebral mental activity, including complex memory functioning and purposeful, goal directed behavior, continues unabated.

As summed up by Nobel Lauriate Roger Sperry (1966, p. 299): "Everything we have seen indicates that the surgery has left these people with two separate minds, that is, two separate spheres of consciousness."

Copyright: 1996, 2000, 2010, 2018 - Rhawn Joseph, Ph.D.