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. Patient suffering from AHS feels that one's hand is possessed by a force outside of ones control and feels 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. Hence, syndrome is name as Alien hand syndrome.The first case of AHS was reported 1908 in German by the preeminent German psychiatrist, Kurt Goldstein. 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.
Causes of AHS:
Different types of brain injuries cause different subtypes alien hand syndrome:
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.
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').
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).
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 collateral 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. found that an irritating alarm activated by biofeedback reduced the time the alien hand held an object.
-Written by Devesh Chaudhari
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