Alien Hand Syndrome

Definition

Definition of Alien Hand Syndrome
Alien hand syndrome is a rare neurological disorder in which one hand functions involuntarily, with the victim completely unaware of its action. While the example above may be extreme, people who suffer from AHS have exhibited similar symptoms in certain cases. Less horrifying symptoms include involuntary reaching and grasping, touching the face or tearing at clothing. More extreme cases have involved involuntarily stuffing food in the mouth, preventing the normal hand from completing simple tasks and self inflicted punching or choking. While it's viewed as more of a nuisance than a medical threat, its sufferers often experience psychological problems and embarrassment and are occasionally put in harm's way as result of the renegade limb's actions.

Symptoms

Symptoms of Alien Hand Syndrome
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 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).

Causes

Causes of Alien Hand Syndrome
A person with the alien hand syndrome can feel sensation in the affected hand but thinks that the hand is not part of their body and that they have no control over its movement, that it belongs to an alien.

Subtypes

Subtypes of Alien Hand Syndrome
There are several distinct subtypes of alien hand syndrome that appear to be associated with specific distributions of associated brain injury.

1. 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) as well as a problem termed "intermanual conflict" in which the two hands appear to be directed at opposing purposes.
2. Frontal Lobe: Unilateral injury to 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 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.

Treatment

Treatment of Alien Hand Syndrome
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 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.