What is alien hand syndrome?

The rare neurological disorder Alien Hand Syndrome (AHS) causes the sufferer's hands to move independently, without his control over the action. People with AHS have been known to punch or choke themselves and tear at their clothing without meaning to do so, and may even need to use the healthy hand to curb the alien hand. The condition typically arises after trauma to the brain, brain surgery, or stroke. "Let's all give it up for E.T.!" {audience applauds}. That's what I thought Alien Hand Syndrome was.