People with alien hand syndrome feel as through their hand is possessed by a force that is outside of one’s control. The hand seems to move on its own, or grab hold of things without the cognitive effort of the individual to whom the arm belongs.
This is most often seen in people who have had the two hemispheres of their brain surgically separated, usually in order to treat severe symptoms of epilepsy. It can also be seen in people who have recently had brain surgery, a stroke, infection, a brain tumor, an aneurysm, or people who have suffered from degenerative brain disorders such as Alzheimer’s and Creutzfeldt-Jakob disease. Each of these things, and therefore alien hand syndrome in general, are associated with the frontal, occipital, and parietal lobes of the brain.
The first known case appeared in a case report that was published in Germany in 1908 by Kurt Goldstein, a preeminent German neuro-psychiatrist. In his paper, he described a right-handed woman who had suffered a stroke that affected her left side; by the time she spoke to Goldstein, she had already partially recovered. However, she described feeling as though her left arm belonged to another person, and performed actions that appeared to occur independent of her will, insisting someone else was moving her hand. His initial diagnosis was that she suffered from paranoia, but upon further observation, he noticed that the somatic sensibility on her left side was significantly impaired, and from these observations, he developed a “doctrine of motor apraxia”, in which he discussed the processes involved in voluntary action.
There are three subtypes of this disorder, resulting from damage to the corpus callosum, frontal lobe, or parietal lobe.
- Corpus Callosum: Damage to the corpus callosum can give rise to purposeful actions in the person’s non-dominant hand (e.g. a person who is left-hemisphere dominant will experience the left hand becoming alien, and the right hand will become alien if the person is right-hemisphere dominant). In the “colossal variant” the patient’s hand counteracts voluntary actions performed by the “good” hand, and people with this variant often have agnostic dyspraxia (involves compulsive automatic execution of motor commands) and diagnostic dyspraxia (involves a conflict between the unaffected hand and the affected hand).
- Frontal Lobe: Unilateral injury to the medial aspect of the brain’s frontal lobe can cause reaching, grabbing, and other purposeful movement in the contralateral hand (the hand opposite the hemisphere of the brain that is affected).
- Parietal Lobe: Damage to the parietal lobe creates a distinct posterior variant form of alien hand syndrome; in this situation, the movements are more likely to withdraw the palm from sustained contact with the surrounding environment, rather than reaching out to make contact with the surface or with environmental stimuli.