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Alien hand syndrome is a rare disorder that typically affects the hand, but can also occur
in the leg.
In a patient suffering from alien hand syndrome, their hand may seem to act independent of
their desires.
It may interact with objects the patient has no desire to interact with, or even interfere
with tasks performed with the other hand.
One early case report described a patient whose own hand tried to choke her.
Many patients also begin to feel that their hand is not actually their own.
Alien hand syndrome most commonly occurs as part of corticobasal syndrome, but there are
many other causes as well, like stroke and Creutzfeldt-Jakob disease.
Although there are a number of areas of the brain that may be damaged in alien hand syndrome,
some of the most common variants of the syndrome involve damage to the corpus callosum, medial
frontal lobe, and/or parietal lobe.
It is still not fully understood how damage to these areas leads to alien hand syndrome,
but researchers have proposed a number of hypotheses.
The corpus callosum is a large collection of nerve fibers that connects the two cerebral
hemispheres.When the corpus callosum is damaged, it may impair the ability of the left and
right cerebral hemispheres to coordinate movement between limbs, and to inhibit unwanted movements
in the alien hand while one is making intentional movements with the functional hand.
The medial frontal lobe contains the supplementary motor area, which is thought to be involved
in the initiation of movement as well as the inhibition of unwanted movements.
Damage to this area thus may lead to an impaired ability to inhibit unwanted movements in the
alien limb.
Because the parietal lobe is an important area for processing sensory information, damage
here may result in a deficit of sensory input from the alien limb, which may contribute
to problems coordinating movement in the alien limb and also lead to the patient perceiving
the limb as foreign.