Alien hand syndrome
Encyclopedia
Alien hand syndrome is a neurological disorder
in which the afflicted person's hand appears to take on a mind of its own. Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain
surgically separated
, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy
. It also occurs in some cases after other brain surgery, stroke
s, or infection
s.
' associated with the purposeful movement of the limb while retaining a sense of 'ownership' of the limb. They feel that they have no control over the movements of the 'alien' hand, but that, instead, the hand has the capability of acting autonomously — i.e., independent of their voluntary control. The hand effectively has 'a will of its own.' "Alien behavior" can be distinguished from reflexive behavior in that the former is flexibly purposive while the latter is obligatory. Sometimes the sufferer will not be aware of what the alien hand is doing until it is brought to his or her attention, or until the hand does something that draws their attention to its behavior.
A related syndrome described by the French neurologist François Lhermitte involves the release through disinhibition of a tendency to compulsively utilize objects that present themselves in the surrounding environment around the patient (Lhermitte 1983; Lhermitte et al. 1986). The behavior of the patient is, in a sense, obligatorily linked to the "affordances"
(using terminology introduced by the American ecological psychologist, James J. Gibson) presented by objects that are located within the immediate peri-personal environment. This condition, termed "utilization behavior
", is most often associated with extensive bilateral frontal lobe damage and might actually be thought of as "bilateral" alien hand syndrome in which the patient is compulsively directed by external environmental contingencies (e.g., the presence of a hairbrush on the table in front of them elicits the act of brushing the hair) and has no capacity to "hold back" and inhibit pre-potent motor programs that are obligatorily linked to the presence of specific external objects in the peri-personal space of the patient. When the frontal lobe damage is bilateral and generally more extensive, the patient completely loses the ability to act in a self-directed manner and becomes totally dependent upon the surrounding environmental indicators to guide his behavior in a general social context, a condition also identified by Lhermitte (1986), and referred to as "Environmental Dependency Syndrome".
Sufferers of alien hand will often personify the rogue limb, for example believing it to be "possessed" by some intelligent or alien spirit or an entity that they may name or identify. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in patients who have sustained damage to the corpus callosum
that connects the two cerebral hemispheres (see also split-brain
), the hands appear to be acting in opposition to each other. For example, one patient was observed putting a cigarette into her mouth with her intact, 'controlled' hand (her right, dominant hand), following which her alien, non-dominant, left hand came up to grasp the cigarette, pull the cigarette out of her mouth, and toss it away before it could be lit by the controlled, dominant, right hand. The patient then surmised that "I guess 'he' doesn't want me to smoke that cigarette." This type of problem has been termed "intermanual conflict" or "diagonistic Ideomotor apraxia
."
can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming alien, and the right hand will turn alien in the person with right-hemisphere dominance) as well as a problem termed "intermanual conflict" in which the two hands appear to be directed at opposing purposes.
can trigger reaching, grasping and other purposeful movements in the contralateral hand. With anteromedial frontal lobe injury, these movements are often exploratory reaching movements in which external objects are frequently grasped and utilized functionally, without the simultaneous perception on the part of the patient that they are "in control" of these movements. Once an object is maintained in the grasp of this "frontal variant" form of alien hand, the patient often has difficulty with voluntarily releasing the object from grasp and can sometimes be seen to be peeling the fingers of the hand back off the grasped object using the opposite controlled hand to enable the release of the grasped object.
and/or occipital lobe
of the brain. The movements in this situation tend to be more likely to withdraw the palmar surface of the hand away from environmental contact rather than reaching out to grasp onto objects to produce palmar tactile stimulation, as is most often seen in the frontal form of the condition. Alien movements in the posterior variant of the syndrome also tend to be less coordinated and show a coarse ataxic motion during active movement that is generally not observed in the frontal form of the condition. The alien limb in the posterior variant of the syndrome may be seen to 'levitate' upward into the air and away from contact surfaces. Alien hand movement in the posterior variant may show a typical posture, sometimes referred to as a 'parietal hand' or 'instinctive avoidance reaction' (a term introduced by neurologist Derek Denny-Brown
), in which the digits move into a highly extended position and the palmar surface is pulled back away from approaching objects. The 'alien' movements, however, remain purposeful and goal-directed, a point which clearly differentiates these movements from other forms of involuntary limb movement (e.g., athetosis
, chorea
, or myoclonus
).
controlling hand movement is isolated from Premotor cortex influences but remains generally intact in its ability to execute movements of the hand.
A 2009 fMRI study looking at the temporal sequence of activation of components of a cortical network associated with voluntary movement in normal individuals demonstrated "an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex". Therefore, with normal voluntary movement, the emergent sense of agency
appears to be associated with an orderly sequence of activation that develops initially in the anteromedial frontal cortex in the vicinity of the supplementary motor complex on the medial surface of the hemisphere prior to activation of the primary motor cortex.
A 2007 fMRI study examining the difference in functional brain activation patterns associated with alien as compared to non-alien 'volitional' movement in a patient with alien hand syndrome found that alien movement involves isolated activation of the contralateral secondary motor cortex, while non-alien movement involved the activation of primary motor cortex in concert with frontal and parietal association cortex presumably involved in a cortical network generating premotor influences on the primary motor cortex.
" that is normally associated with voluntary movement is impaired or lost. There is a dissociation between the process associated with the actual execution of the physical movements of the limb and the process that produces an internal sense of voluntary control over the movements, with this latter process thus normally creating the internal conscious sensation that the movements are being internally initiated, controlled and produced by an active self.
Recent studies have examined the neural correlates of emergence of the sense of agency
under normal circumstances. This appears to involve consistent congruence between what is being produced through efferent outflow to the musculature of the body, and what is being sensed as the presumed product in the periphery of this efferent command signal. In alien hand syndrome, the neural mechanisms involved in establishing that this congruence has occurred may be impaired. This may involve an abnormality in the brain mechanism that differentiates between "re-afference" (i.e., the return of kinesthetic sensation from the self-generated 'active' limb movement) and "ex-afference" (i.e., kinesthetic sensation generated from an externally-produced 'passive' limb movement in which an active self does not participate). This brain mechanism is proposed to involve the production of a parallel "efference copy" signal that is sent directly to the somatic sensory regions and is transformed into a "corollary discharge," an expected afferent signal from the periphery that would result from the performance driven by the issued efferent signal. The correlation of the corollary discharge signal with the actual afferent signal returned from the periphery can then be used to determine if, in fact, the intended action occurred as expected. When the sensed result of the action is congruent with the predicted result, then the action can be labelled as self-generated and associated with an emergent sense of agency
.
If, however, the neural mechanisms involved in establishing this sensorimotor linkage associated with self-generated action are faulty, it would be expected that the sense of agency
with action would not develop.
When the anteromedial frontal "escape" system is damaged, involuntary but purposive movements of an exploratory reach-and-grasp nature—what Denny-Brown (1956, 1966) referred to as a positive cortical tropism—are released in the contralateral limb. This is referred to as a positive cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that increases or enhances the eliciting stimulation through a positive feedback connection.
When the posterolateral parieto-occipital "approach" system is damaged, involuntary purposive movements of a release-and-retract nature, such as levitation and instinctive avoidance—what Denny-Brown (1956, 1966) referred to as a negative cortical tropism—are released in the contralateral limb. This is referred to as a negative cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that reduces or eliminates the eliciting stimulation through a negative feedback connection.
Each intrahemispheric agency system has the potential capability of acting autonomously in its control over the contralateral limb although unitary integrative control of the two hands is maintained through interhemispheric communication between these systems via the projections traversing the corpus callosum
at the cortical level and other interhemispheric commissures linking the two hemispheres at the subcortical level.
When there is a major disconnection between the two hemispheres resulting from callosal injury, the language-linked dominant hemisphere agent which maintains its primary control over the dominant limb loses, to some degree, its direct and linked control over the separate "agent" based in the nondominant hemisphere, and the nondominant limb, which had been previously responsive and "obedient" to the dominant conscious agent. The possibility of purposeful action occurring outside of the realm of influence of the conscious dominant agent can occur and the basic assumption that both hands are controlled through and subject to the dominant agent is proven incorrect. The sense of agency that would normally arise from movement of the nondominant limb now no longer develops, or, at least, is no longer accessible to consciousness. A new explanatory "story" for understanding the nature of the inaccessible agent moving the nondominant limb is necessitated.
Under such circumstances, the two agents that can direct actions in the two limbs that are directed at opposing purposes although the dominant hand remains linked to the dominant consciously accessible agent and is viewed as continuing to be under "conscious control" and obedient to conscious will, while the nondominant hand is no longer "tied in" to the dominant agent and is thus identified by the conscious language-based dominant agent as having a separate and alien agency. This theory would explain the emergence of alien behavior in the nondominant limb and intermanual conflict between the two limbs in the presence of damage to the corpus callosum.
The distinct anteromedial, frontal, and posterolateral temporo-parieto-occipital forms of the alien hand syndrome would be explained by selective injury to either the frontal or the posterior agency systems within a particular hemisphere, with the alien behavior developing in the limb contralateral to the damaged hemisphere.
In the presence of unilateral damage to a single cerebral hemisphere, there is generally a gradual reduction in the frequency of alien behaviors observed over time and a gradual restoration of voluntary control over the affected hand. One theory is that neuroplasticity
in the bihemispheric and subcortical brain systems involved in voluntary movement production can serve to re-establish the connection between the executive production process and the internal self-generation and registration process. Exactly how this may occur is not well understood, but a process of gradual recovery from alien hand syndrome when the damage involves a single hemisphere has been reported.
In another approach, the patient is trained to perform a specific task, such as moving the alien hand to contact a specific object or a highly salient environmental target, which is a movement that the patient can learn to generate voluntarily through focused training in order to effectively override the alien behavior. It is possible that some of this training produces a re-organization of premotor systems within the damaged hemisphere, or, alternatively, that ipsilateral control of the limb from the intact hemisphere may be expanded. Another method involves simultaneously "muffling" the action of the alien hand and limiting the sensory feedback coming back to the hand from environmental contact by placing it in a restrictive "cloak" such as a specialized soft foam hand orthosis or, alternatively, an everyday oven mitt. Of course, this can limit the degree to which the hand can participate in addressing functional goals for the patient. Theoretically, this approach could slow down the process through which voluntary control of the hand is restored if the neuroplasticity that underlies recovery involves the exercise of voluntary will to control the actions of the hand in a functional context.
Neurological disorder
A neurological disorder is a disorder of the body's nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord, or in the nerves leading to or from them, can result in symptoms such as paralysis, muscle weakness, poor coordination, loss of sensation, seizures,...
in which the afflicted person's hand appears to take on a mind of its own. Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
surgically separated
Corpus callosotomy
Corpus callosotomy is a surgical procedure that disconnects the cerebral hemispheres, resulting in a condition called split-brain....
, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
. It also occurs in some cases after other brain surgery, stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
s, or infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s.
Symptoms
A person with alien hand syndrome can feel normal sensation in the hand and leg, but believes that the hand, while still being a part of their body, behaves in a manner that is totally distinct from the sufferer's normal behavior. They lose the 'sense of agencySense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
' associated with the purposeful movement of the limb while retaining a sense of 'ownership' of the limb. They feel that they have no control over the movements of the 'alien' hand, but that, instead, the hand has the capability of acting autonomously — i.e., independent of their voluntary control. The hand effectively has 'a will of its own.' "Alien behavior" can be distinguished from reflexive behavior in that the former is flexibly purposive while the latter is obligatory. Sometimes the sufferer will not be aware of what the alien hand is doing until it is brought to his or her attention, or until the hand does something that draws their attention to its behavior.
A related syndrome described by the French neurologist François Lhermitte involves the release through disinhibition of a tendency to compulsively utilize objects that present themselves in the surrounding environment around the patient (Lhermitte 1983; Lhermitte et al. 1986). The behavior of the patient is, in a sense, obligatorily linked to the "affordances"
Affordance
An affordance is a quality of an object, or an environment, which allows an individual to perform an action. For example, a knob affords twisting, and perhaps pushing, while a cord affords pulling...
(using terminology introduced by the American ecological psychologist, James J. Gibson) presented by objects that are located within the immediate peri-personal environment. This condition, termed "utilization behavior
Utilization behavior
Utilization behavior is a type of neurobehavioral disorder that involves patients grabbing objects in view and starting the 'appropriate' behavior associated with it at an 'inappropriate' time. Utilization behavior patients have difficulty resisting the impulse to operate or manipulate objects...
", is most often associated with extensive bilateral frontal lobe damage and might actually be thought of as "bilateral" alien hand syndrome in which the patient is compulsively directed by external environmental contingencies (e.g., the presence of a hairbrush on the table in front of them elicits the act of brushing the hair) and has no capacity to "hold back" and inhibit pre-potent motor programs that are obligatorily linked to the presence of specific external objects in the peri-personal space of the patient. When the frontal lobe damage is bilateral and generally more extensive, the patient completely loses the ability to act in a self-directed manner and becomes totally dependent upon the surrounding environmental indicators to guide his behavior in a general social context, a condition also identified by Lhermitte (1986), and referred to as "Environmental Dependency Syndrome".
Sufferers of alien hand will often personify the rogue limb, for example believing it to be "possessed" by some intelligent or alien spirit or an entity that they may name or identify. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in patients who have sustained damage to the corpus callosum
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
that connects the two cerebral hemispheres (see also split-brain
Split-brain
Split-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. The surgical operation to produce this condition is called corpus callosotomy and is usually used as a last resort to treat otherwise intractable epilepsy...
), the hands appear to be acting in opposition to each other. For example, one patient was observed putting a cigarette into her mouth with her intact, 'controlled' hand (her right, dominant hand), following which her alien, non-dominant, left hand came up to grasp the cigarette, pull the cigarette out of her mouth, and toss it away before it could be lit by the controlled, dominant, right hand. The patient then surmised that "I guess 'he' doesn't want me to smoke that cigarette." This type of problem has been termed "intermanual conflict" or "diagonistic Ideomotor apraxia
Apraxia
Apraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements...
."
Subtypes
There are several distinct subtypes of alien hand syndrome that appear to be associated with specific distributions of associated brain injury.Corpus Callosum
Damage to the corpus callosumCorpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming alien, and the right hand will turn alien in the person with right-hemisphere dominance) as well as a problem termed "intermanual conflict" in which the two hands appear to be directed at opposing purposes.
Frontal lobe
Unilateral injury to the brain's frontal lobeFrontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
can trigger reaching, grasping and other purposeful movements in the contralateral hand. With anteromedial frontal lobe injury, these movements are often exploratory reaching movements in which external objects are frequently grasped and utilized functionally, without the simultaneous perception on the part of the patient that they are "in control" of these movements. Once an object is maintained in the grasp of this "frontal variant" form of alien hand, the patient often has difficulty with voluntarily releasing the object from grasp and can sometimes be seen to be peeling the fingers of the hand back off the grasped object using the opposite controlled hand to enable the release of the grasped object.
Parietal and occipital lobes
A distinct "posterior variant" form of alien hand syndrome is associated with damage to the posterolateral parietal lobeParietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
and/or occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
of the brain. The movements in this situation tend to be more likely to withdraw the palmar surface of the hand away from environmental contact rather than reaching out to grasp onto objects to produce palmar tactile stimulation, as is most often seen in the frontal form of the condition. Alien movements in the posterior variant of the syndrome also tend to be less coordinated and show a coarse ataxic motion during active movement that is generally not observed in the frontal form of the condition. The alien limb in the posterior variant of the syndrome may be seen to 'levitate' upward into the air and away from contact surfaces. Alien hand movement in the posterior variant may show a typical posture, sometimes referred to as a 'parietal hand' or 'instinctive avoidance reaction' (a term introduced by neurologist Derek Denny-Brown
Derek Denny-Brown (doctor)
Derek Ernest Denny-Brown OBE was a neurologist. Working in Oxford, London and Boston, he made major contributions to the field of neurology, such as the development of electromyography, physiology of micturition and the treatment of Wilson's disease.-Biography:Born in New Zealand, he studied at...
), in which the digits move into a highly extended position and the palmar surface is pulled back away from approaching objects. The 'alien' movements, however, remain purposeful and goal-directed, a point which clearly differentiates these movements from other forms of involuntary limb movement (e.g., athetosis
Athetosis
Athetosis is a symptom characterized by involuntary convoluted, writhing movements of the fingers, arms, legs, and neck. Movements typical of athetosis are sometimes called athetoid movements. Lesions to the brain are most often the direct cause of the symptoms, particularly to thecorpus striatum...
, chorea
Chorea (disease)
Choreia is an abnormal involuntary movement disorder, one of a group of neurological disorders called dyskinesias. The term choreia is derived from the Greek word χορεία , see choreia , as the quick movements of the feet or hands are vaguely comparable to dancing or piano playing.The term...
, or myoclonus
Myoclonus
Myoclonus is brief, involuntary twitching of a muscle or a group of muscles. It describes a medical sign and, generally, is not a diagnosis of a disease. Brief twitches are perfectly normal. The myoclonic twitches are usually caused by sudden muscle contractions; they also can result from brief...
).
Similarities between frontal and posterior variants
In both the frontal and the posterior variants of the alien hand syndrome, the patient's reactions to the limb's apparent capability to perform goal-directed actions independent of conscious volition is similar. In both of these variants of alien hand syndrome, the alien hand emerges in the hand contralateral to the damaged hemisphere.Explanatory theories
The common emerging factor in alien hand syndrome is that the primary motor cortexPrimary motor cortex
The primary motor cortex is a brain region that in humans is located in the posterior portion of the frontal lobe. Itworks in association with pre-motor areas to plan and execute movements. M1 contains large neurons known as Betz cells, which send long axons down the spinal cord to synapse onto...
controlling hand movement is isolated from Premotor cortex influences but remains generally intact in its ability to execute movements of the hand.
A 2009 fMRI study looking at the temporal sequence of activation of components of a cortical network associated with voluntary movement in normal individuals demonstrated "an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex". Therefore, with normal voluntary movement, the emergent sense of agency
Sense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
appears to be associated with an orderly sequence of activation that develops initially in the anteromedial frontal cortex in the vicinity of the supplementary motor complex on the medial surface of the hemisphere prior to activation of the primary motor cortex.
A 2007 fMRI study examining the difference in functional brain activation patterns associated with alien as compared to non-alien 'volitional' movement in a patient with alien hand syndrome found that alien movement involves isolated activation of the contralateral secondary motor cortex, while non-alien movement involved the activation of primary motor cortex in concert with frontal and parietal association cortex presumably involved in a cortical network generating premotor influences on the primary motor cortex.
Disconnection
It is theorized that alien hand syndrome results when disconnection occurs between different parts of the brain that are engaged in different aspects of the control of bodily movement. As a result, different regions of the brain are able to command bodily movements, but cannot generate a conscious feeling of self-control over these movements. As a result, the "sense of agencySense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
" that is normally associated with voluntary movement is impaired or lost. There is a dissociation between the process associated with the actual execution of the physical movements of the limb and the process that produces an internal sense of voluntary control over the movements, with this latter process thus normally creating the internal conscious sensation that the movements are being internally initiated, controlled and produced by an active self.
Recent studies have examined the neural correlates of emergence of the sense of agency
Sense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
under normal circumstances. This appears to involve consistent congruence between what is being produced through efferent outflow to the musculature of the body, and what is being sensed as the presumed product in the periphery of this efferent command signal. In alien hand syndrome, the neural mechanisms involved in establishing that this congruence has occurred may be impaired. This may involve an abnormality in the brain mechanism that differentiates between "re-afference" (i.e., the return of kinesthetic sensation from the self-generated 'active' limb movement) and "ex-afference" (i.e., kinesthetic sensation generated from an externally-produced 'passive' limb movement in which an active self does not participate). This brain mechanism is proposed to involve the production of a parallel "efference copy" signal that is sent directly to the somatic sensory regions and is transformed into a "corollary discharge," an expected afferent signal from the periphery that would result from the performance driven by the issued efferent signal. The correlation of the corollary discharge signal with the actual afferent signal returned from the periphery can then be used to determine if, in fact, the intended action occurred as expected. When the sensed result of the action is congruent with the predicted result, then the action can be labelled as self-generated and associated with an emergent sense of agency
Sense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
.
If, however, the neural mechanisms involved in establishing this sensorimotor linkage associated with self-generated action are faulty, it would be expected that the sense of agency
Sense of agency
The "sense of agency" refers to the subjective awareness that one is initiating, executing, and controlling one's own volitional actions in the world. It is the pre-reflective awareness or implicit sense that it is me who is presently executing bodily movement or thinking thoughts...
with action would not develop.
Loss of inhibitions
One theory posed to explain these phenomena proposes that the brain has separable neural "premotor" or "agency" systems for managing the process of transforming intentions into overt action. An anteromedial frontal premotor system is engaged in the process of directing exploratory actions based on "internal" drive by releasing or reducing inhibitory control over such actions. Damage to this system produces disinhibition and release of such actions which then occur autonomously. A posterolateral temporo-parieto-occipital premotor system has a similar inhibitory control over actions that withdraw from environmental stimuli as well as the ability to excite actions that are contingent upon and driven by external stimulation, as distinct from internal drive. These two intrahemispheric systems, each of which activates an opposing cortical "tropism", interact through mutual inhibition that maintains a dynamic balance between approaching toward (ie. with "intent-to-capture" in which contact with and grasping onto the attended object is sought) versus withdrawing from (ie. with "intent-to-escape" in which distancing from the attended object is sought) environmental stimuli in the behavior of the contralateral limbs (Denny-Brown, 1956, 1958, 1966). Together, these two intrahemispheric agency systems form an integrated transhemispheric agency system.When the anteromedial frontal "escape" system is damaged, involuntary but purposive movements of an exploratory reach-and-grasp nature—what Denny-Brown (1956, 1966) referred to as a positive cortical tropism—are released in the contralateral limb. This is referred to as a positive cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that increases or enhances the eliciting stimulation through a positive feedback connection.
When the posterolateral parieto-occipital "approach" system is damaged, involuntary purposive movements of a release-and-retract nature, such as levitation and instinctive avoidance—what Denny-Brown (1956, 1966) referred to as a negative cortical tropism—are released in the contralateral limb. This is referred to as a negative cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that reduces or eliminates the eliciting stimulation through a negative feedback connection.
Each intrahemispheric agency system has the potential capability of acting autonomously in its control over the contralateral limb although unitary integrative control of the two hands is maintained through interhemispheric communication between these systems via the projections traversing the corpus callosum
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
at the cortical level and other interhemispheric commissures linking the two hemispheres at the subcortical level.
Disconnection of hemispheres due to injury
One major difference between the two hemispheres is the direct connection between the agency system of the dominant hemisphere and the encoding system based primarily in the dominant hemisphere that links action production and its interpretation with language. The overarching unitary conscious agent that emerges in the intact brain is based primarily in the dominant hemisphere and is closely connected to the organization of language capacity. It is proposed that while action precedes linguistic capacity during development, a process ensues through the course of development through which linguistic constructs are linked to action elements in order to produce a language-based encoding of action-oriented knowledge.When there is a major disconnection between the two hemispheres resulting from callosal injury, the language-linked dominant hemisphere agent which maintains its primary control over the dominant limb loses, to some degree, its direct and linked control over the separate "agent" based in the nondominant hemisphere, and the nondominant limb, which had been previously responsive and "obedient" to the dominant conscious agent. The possibility of purposeful action occurring outside of the realm of influence of the conscious dominant agent can occur and the basic assumption that both hands are controlled through and subject to the dominant agent is proven incorrect. The sense of agency that would normally arise from movement of the nondominant limb now no longer develops, or, at least, is no longer accessible to consciousness. A new explanatory "story" for understanding the nature of the inaccessible agent moving the nondominant limb is necessitated.
Under such circumstances, the two agents that can direct actions in the two limbs that are directed at opposing purposes although the dominant hand remains linked to the dominant consciously accessible agent and is viewed as continuing to be under "conscious control" and obedient to conscious will, while the nondominant hand is no longer "tied in" to the dominant agent and is thus identified by the conscious language-based dominant agent as having a separate and alien agency. This theory would explain the emergence of alien behavior in the nondominant limb and intermanual conflict between the two limbs in the presence of damage to the corpus callosum.
The distinct anteromedial, frontal, and posterolateral temporo-parieto-occipital forms of the alien hand syndrome would be explained by selective injury to either the frontal or the posterior agency systems within a particular hemisphere, with the alien behavior developing in the limb contralateral to the damaged hemisphere.
Treatment
Although there is no known formal (primary) treatment for alien hand syndrome at this time, the symptoms can be reduced and managed to some degree by keeping the alien hand occupied and involved in a task, for example by giving it an object to hold in its grasp. Specific learned tasks can restore voluntary control of the hand to a significant degree. One patient with the "frontal" form of alien hand who would reach out to grasp onto different objects (e.g., door handles) as he was walking was given a cane to hold in the alien hand while walking, even though he really did not need a cane for its usual purpose of assisting with balance and facilitating ambulation. With the cane firmly in the grasp of the alien hand, it would generally not release the grasp and drop the cane in order to reach out to grasp onto a different object. Different strategies can be employed to reduce the interference of the alien hand behavior on the ongoing coherent controlled bodily actions of the patient.In the presence of unilateral damage to a single cerebral hemisphere, there is generally a gradual reduction in the frequency of alien behaviors observed over time and a gradual restoration of voluntary control over the affected hand. One theory is that neuroplasticity
Neuroplasticity
Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
in the bihemispheric and subcortical brain systems involved in voluntary movement production can serve to re-establish the connection between the executive production process and the internal self-generation and registration process. Exactly how this may occur is not well understood, but a process of gradual recovery from alien hand syndrome when the damage involves a single hemisphere has been reported.
In another approach, the patient is trained to perform a specific task, such as moving the alien hand to contact a specific object or a highly salient environmental target, which is a movement that the patient can learn to generate voluntarily through focused training in order to effectively override the alien behavior. It is possible that some of this training produces a re-organization of premotor systems within the damaged hemisphere, or, alternatively, that ipsilateral control of the limb from the intact hemisphere may be expanded. Another method involves simultaneously "muffling" the action of the alien hand and limiting the sensory feedback coming back to the hand from environmental contact by placing it in a restrictive "cloak" such as a specialized soft foam hand orthosis or, alternatively, an everyday oven mitt. Of course, this can limit the degree to which the hand can participate in addressing functional goals for the patient. Theoretically, this approach could slow down the process through which voluntary control of the hand is restored if the neuroplasticity that underlies recovery involves the exercise of voluntary will to control the actions of the hand in a functional context.
In popular culture
- In Stanley KubrickStanley KubrickStanley Kubrick was an American film director, writer, producer, and photographer who lived in England during most of the last four decades of his career...
's 1964 film, Dr. Strangelove, the eponymous character played by Peter SellersPeter SellersRichard Henry Sellers, CBE , known as Peter Sellers, was a British comedian and actor. Perhaps best known as Chief Inspector Clouseau in The Pink Panther film series, he is also notable for playing three different characters in Dr...
is shown to be suffering from alien hand syndrome. - The film Idle HandsIdle HandsIdle Hands is a 1999 horror comedy film directed by Rodman Flender, written by Terri Hughes and Ron Milbauer, and starring Devon Sawa, Seth Green, Elden Henson, Jessica Alba, and Vivica A. Fox...
is very loosely based on the conditions associated with alien hand syndrome. - In Tales of Monkey IslandTales of Monkey IslandTales of Monkey Island is a 2009 graphic adventure video game developed by Telltale Games and LucasArts. It is the fifth game in the Monkey Island series, released nearly a decade after the previous installment, Escape from Monkey Island. Developed for Windows and the Wii console, the game was...
, Guybrush ThreepwoodGuybrush ThreepwoodGuybrush Ulysses Threepwood is the main character of the Monkey Island series of computer adventure games by LucasArts. The voice of Guybrush is actor Dominic Armato in the third, fourth and fifth games, as well as the enhanced remakes of The Secret of Monkey Island and Monkey Island 2: LeChuck's...
's poxed hand also has a mind of its own, providing a comical effect. - In the HouseHouse (TV series)House is an American television medical drama that debuted on the Fox network on November 16, 2004. The show's central character is Dr. Gregory House , an unconventional and misanthropic medical genius who heads a team of diagnosticians at the fictional Princeton-Plainsboro Teaching Hospital in...
episode "Both Sides NowBoth Sides Now (House)"Both Sides Now" is the twenty-fourth episode and season finale of the fifth season of House. It originally aired on May 11, 2009.-Plot:...
", the patient suffers from alien hand syndrome. - In The Evil DeadThe Evil Dead (franchise)The Evil Dead is a trilogy of horror films created by Sam Raimi. The films focus on the protagonist, Ashley "Ash" J. Williams, played by Bruce Campbell, who deals with "deadites", which are undead antagonists created by the Necronomicon Ex-Mortis. The film series has since expanded into other...
the lead character Ash's hand becomes possessed.
Selected references from medical literature
External links
- Recent review article on Alien Hand Syndrome by LA Scepkowski & A Cronin-Golomb
- Editorial paper regarding the different forms of Alien Hand Syndrome by G Goldberg
- Recent review article from the Archives of Neurology by I. Biran and A. Chatterjee
- Information about the rare disorder, as well as how many times it has influenced the media.
- BBC Video: Woman with Alien Hand Syndrome