Alien hand syndrome

Alien hand syndrome, (AHS) is a rare neurological disorder that causes hand movement without the person being aware of what is happening or having control over the action. The afflicted person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the healthy hand to restrain the alien hand.

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 brain surgery, stroke, infection, tumor, aneurysm and specific degenerative brain conditions such as Alzheimer's disease and Creutzfeldtâ€"Jakob disease. Other areas of the brain that are associated with alien hand syndrome are the frontal, occipital and parietal lobes.

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

The patient complained of a feeling of "strangeness" in relationship to the goal-directed movements of the left hand and insisted that "someone else" was moving the left hand, and that she was not moving it herself. Goldstein reported that, as a result of this report, "she was regarded at first as a paranoiac." When the left hand grasped an object, she could not voluntarily release it. The somatic sensibility of the left side was reported to be impaired, especially with aspects of sensation having to do with the orienting of the limb. Some spontaneous movements were noted to occur involving the left hand, such as wiping the face or rubbing the eyes; but these were relatively infrequent. Only with significant effort was she able to perform simple movements with the left arm in response to spoken command, but these movements were performed slowly and often incompletely even if these same movements had been involuntarily performed with relative ease before while in the abnormal 'alien' control mode.

Based on these remarkable observations, Goldstein developed a "doctrine of motor apraxia" in which he discussed the process involved in the generation of voluntary action and interpreted these findings in the context of a proposed central structure organized around the perception and internal representation of the space-time continuum encompassing memory, will, and other higher cognitive processes. Goldstein maintained that a unified conceptual organization and general gestalt of space-time in which all aspects of relevant sensory perception of both the physical body (i.e. via interoception) and external space (i.e. via exteroception) were integrated was necessary both for object perception as well as for successful goal-directed dynamic bodily action in relationship to extrapersonal space and the objects located therein. In his classic papers reviewing the wide variety of disconnection syndromes associated with focal brain pathology, Norman Geschwind commented that Kurt Goldstein "was perhaps the first to stress the non-unity of the personality in patients with callosal section, and its possible psychiatric effects."

Anarchic hand syndrome and alien hand syndrome are two similar but separate disorders. In both there are unintended but purposeful and autonomous movements of the upper limb and intermanual conflict. Anarchic hand is usually diagnosed as opposed to alien hand syndrome because it tends to be more associated with motor impairments as the patients acknowledge the hand as theirs but are frustrated by its unintended actions. In alien hand syndrome the individual tends to display more sensory deficits as they dissociate themselves from the hand and its actions, frequently remarking on the hand's behaviour as if it does not belong to them.

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 agency' 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 autonomouslyâ€"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. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in patients who have sustained damage to the corpus callosum that connects the two cerebral hemispheres (see also split-brain), the hands appear to be acting in opposition to each other.

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

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

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

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

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

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

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

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

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

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

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

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

Frontal lobe

Unilateral injury to the mesial aspect of the brain's frontal lobe can trigger reaching, grasping and other purposeful movements in the contralateral hand. With anteromedial frontal lobe injuries, these movements are often exploratory reaching movements in which external objects are frequently grasped and utilized functionally, without the simultaneous perception on the part of the patient that they are "in control" of these movements. Once an object has been acquired and is maintained in the grasp of this "frontal variant" form of alien hand, the patient often has difficulty with voluntarily releasing the object from grasp and can sometimes be seen to be peeling the fingers of the hand back off the grasped object using the opposite controlled hand to enable the release of the grasped object (also referred to as tonic grasping or the 'instinctive grasp reaction'). Some (for example, the neurologist Derek Denny-Brown) have referred to this behavior as "magnetic apraxia" (see: http://emedicine.medscape.com/article/1136037-overview/ ).

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

Parietal and occipital lobes

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

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

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

Similarities between frontal and posterior variants

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

Explanatory theories

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

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

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

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

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

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

Disconnection

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

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

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

Loss of inhibitions

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

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

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

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

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

Disconnection of hemispheres due to injury

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

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

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

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

Treatment

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

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

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

Another method involves simultaneously "muffling" the action of the alien hand and limiting the sensory feedback coming back to the hand from environmental contact by placing it in a restrictive "cloak" such as a specialized soft foam hand orthosis or, alternatively, an everyday oven mitt. Other patients have reported using an orthotic device to restrict perseverative grasping or restraining the alien hand by securing it to the bed pole. Of course, this can limit the degree to which the hand can participate in addressing functional goals for the patient and may be considered to be an unjustifiable restraint.

Theoretically, this approach could slow down the process through which voluntary control of the hand is restored if the neuroplasticity that underlies recovery involves the recurrent exercise of voluntary will to control the actions of the hand in a functional context and the associated experiential reinforcement through successful willful suppression of the alien behavior.

In popular culture

• In Stanley Kubrick's 1964 film, Dr. Strangelove, the eponymous character played by Peter Sellers is shown to be suffering from alien hand syndrome, hence the condition's common association with the character.
• In the House episode "Both Sides Now", the patient suffers from alien hand syndrome.
• In L'Arbre des Possibilitées by Bernard Werber a policeman has a hand that commits murder while suffering from alien hand syndrome.
• An episode of Dark Matters: Twisted But Trueâ€"a documentary show on Discovery Scienceâ€"described alien hand syndrome and traced its history.
• A severed corpus callosum plays a major part in the plot of Stanislaw Lem's novel Peace on Earth.
• In the South Park episode "Fat Butt and Pancake Head", Eric Cartman suffers from alien hand syndrome.