Alien hand syndrome

Alien hand syndrome (anarchic hand or Dr. Strangelove syndrome) is an unusual neurological disorder in which one of the sufferer's hands seems to take on a life of its own. AHS 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, strokes, or infections. more...

Symptoms

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 themselves. They feel that they have no control over the movements of their alien hand, but that, instead, the hand has the capability of acting independent of their conscious control. Alien hands can perform complex acts such as undoing buttons or removing clothing. Sometimes the sufferer will not be aware of what the hand is doing until it is brought to his or her attention. Sufferers of Alien Hand will often personify the rogue limb, for example believing it "possessed" by some intelligent or alien spirit, 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, the hands appear to be acting in opposition to each other. For example, one patient was observed to be putting a cigarette into her mouth with her intact 'controlled' hand (as might be expected, her right dominant hand), following which her alien opposite nondominant left hand then came up to grasp the cigarette, pull the cigarette out of the mouth, and toss it away before it could be lit by the controlled dominant right hand. The patient then surmised that "I guess she 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 (psychology), as well as the general nature of human agency. 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.

Causes and treatment

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 (eg. 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.

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