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Alien hand syndrome
Additional recommended knowledge
An alien hand sufferer can feel normal sensation in the hand, 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 feel that they have no control over the movements of the 'alien' hand, but that, instead, the hand has the capability of acting independent of their conscious voluntary control. Alien hands can perform complex acts such as undoing buttons, removing clothing, and manipulation of tools. 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 Francois L'Hermitte 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, J.J. Gibson) presented by objects that are located within the immediate 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) 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 their behavior, a condition also identified by L'Hermitte, and referred to as "Environmental Dependency Syndrome".
Sufferers of Alien Hand will often personify the rogue limb, for example believing it "possessed" by some intelligent or alien spirit or entity that they may name or identify, and may fight or punish it in an attempt to control it. 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 apraxia".
This condition has been thought to provide a fascinating window into the nature of human consciousness as it relates to voluntary action, processes underlying decision making and conscious volition, as well as the general nature of human agency and intentionality. Besides its relevancy to the understanding of the neurobiologic basis of human action, these observations would appear to have significant relevance for the general philosophy of action. In that the recognition of this condition depends upon linking an observation of a particular behavior--the appearance of a purposeful limb behavior--to either a direct report or inference regarding the experience of the actor in the course of producing the movement, and then correlating this relation to brain pathophysiology, alien hand syndrome and its study may be viewed as within the purview of neurophenomenology.
There are several distinct subtypes of Alien Hand that appear to be associated with specific types of triggering brain injury. Damage to the corpus callosum can give rise to "purposeful" actions in the sufferer's non-dominant hand (a right-handed sufferer's left hand will turn alien, and the right hand will turn alien in the left-handed) as well as a problem termed "intermanual conflict" in which the two hands appear to be directed at opposing purposes, whereas unilateral injury to the brain's frontal lobe can trigger reaching, grasping and other purposeful movements in the contralateral hand. With 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 the "frontal" 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.
A distinct "posterior" form of alien hand syndrome is associated with damage to the 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 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 form of the syndrome also tend to be less coordinated and show a coarse ataxic motion that is generally not observed in the frontal form of the condition. The alien limb in the posterior form of the syndrome may be seen to 'levitate' upward and away from contact surfaces. Alien hand movement in the posterior form 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 fully 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., chorea, or myoclonus). In both the frontal and the posterior forms 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.
Patients thus will often indicate that the apparently purposeful movements of the alien hand are "wayward" or "disobedient", in that they are not being generated through the exertion of their own voluntary will or directed toward goals that have been consciously produced, but, instead, the alien hand appears to behave independent of conscious will, effectively "on its own". The alien hand may even engage in socially inappropriate behavior in a public venue causing significant embarrassment and distress. Patients may react with dismay and concern at the ability of the hand to perform purposeful actions that are independent of their own sense of control over the movement, a phenomenon termed "auto-criticism".
Alternatively, they may attribute the forces initiating and controlling these purposeful movements to some external being that is somehow "alien" to their self-perceived being. For example, a particularly religious woman with alien hand syndrome, when asked who or what was actually controlling the alien movements of her hand, replied that "God must be doing all of that". Some patients choose to "personify" the hand and dissociate themselves from the behavior of the hand by giving it a proper name and attributing to it a separate and distinct personality and personhood. They may choose to "hold back" these unwanted "alien" movements and behaviors by grasping and constraining the "wayward" hand with the controlled contralateral hand, an action that has been termed "self-restriction" or "self-grasping". Injuries to the cerebral cortex can give rise to aimless movements of either hand, and more complex alien hand movements are usually associated with brain tumors, aneurysm or stroke. Such alien movements and behaviors can also be seen in progressive degenerative diseases that produce a process of steady disintegration within the central nervous system, such as Creutzfeldt-Jakob Disease, and corticobasal degeneration.
Alien hand syndrome is due to damage in the medial motor frontal region of the brain.
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. There is thus 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 creating the internal conscious sensation that the movements are being internally initiated, controlled and produced by an active self. 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).
One theory posed to explain these phenomena proposes that the brain has separable neural "premotor" or "agency" systems for managing the process of transforming intent into overt action. A medial frontal 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 lateral parieto-occipital 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 hemispheric systems interact through mutual inhibition that maintains a balance between responding to and withdrawing from environmental stimuli in the behavior of the contralateral limbs. Together, these hemispheric agency systems form an integrated intrahemispheric agency system.
When the medial frontal component system is damaged, involuntary but purposive movements of an exploratory reach-and-grasp nature are released in the contralateral limb. When the posterior parieto-occipital system is damaged, involuntary purposive movements of a release-and-retract nature are released. Furthermore, each intrahemispheric agency system has the capability of acting autonomously in its control over the contralateral limb although unitary control is maintained through interhemispheric communication between these systems via the corpus callosum at the cortical level and other interhemispheric commissures linking the two hemispheres at the subcortical level. Thus, human agency can be thought of as emerging through the linked and coordinated action of at least four major agency systems, two in each hemisphere.
The critical difference between the two hemispheres, however, is the connection between the agency system in the dominant hemisphere and the encoding system based primarily in the dominant hemisphere that links action production and interpretation with language. Thus, the overarching unitary 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. Through this process of basically "telling oneself a story" about how an act occurs, a language-based "action-capable" self is constructed.
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 effectively loses its direct and linked control over the separate "agent" based in the nondominant hemisphere (and, thus, the nondominant limb), which had been previously responsive and "obedient" to the dominant agent. The possibility of purposeful action occurring outside of the realm of influence of the dominant agent, thus can occur and the basic assumption that both hands are controlled through and subject to the dominant agent is proven incorrect. A new explanatory "story" is thus necessitated.
Under such circumstances, the two agents therefore can direct actions in the two limbs that are directed at opposing purposes although the dominant hand remains linked to the dominant agent and is thus 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 frontal and posterior 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.
Proposed strategies for 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. Also, specific learned tasks can restore voluntary control of the hand to a significant degree. For example, 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. Thus, different strategies can be employed to reduce the interference of the alien hand behavior on the ongoing coherent controlled actions of the patient.
Furthermore, 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, suggesting 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 training in order to effectively override the alien behavior. Yet another approach 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 then limits the degree to which the hand can subserve 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.
There is a deep human fascination with the possibility of dissociation of intent from action/behavior and its implications. This is because of the deeply held belief in "common-sense" psychology regarding the unitary nature of behavior (i.e. that there is a single 'agent' within a single being generally built into its central nervous system) and the necessity for being able to hold a person (i.e., conscious behaving human agent) directly responsible for the production and therefore the consequences of his actions produced through the physical movement of his body segments. When this general "rule" or widely held belief regarding nature is transgressed by nature, the recognition of such disturbance has significant impact. Hence, the potential to move and entertain us and to be picked up and incorporated into various cultural references and fictional accounts that derive from a core of truth and observed reality.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Alien_hand_syndrome". A list of authors is available in Wikipedia.|