How Your Brain Can Drain Your Hand

A new study says hypnotists can paralyse your hand by simply butting in on the process that normally makes it move

How can a hypnotist paralyse your hand simply with words? By making a part of your brain butt in on the process that normally makes your hand move, says a study. So the brain region that’s ready to move your hand ignores its usual inputs and listens to this interloper. The study, conducted by the University of Geneva in Switzerland, used brain scans to show what happened when 12 volunteers tried to move a hand paralysed by hypnosis. Results showed the right motor cortex prepared itself as usual to tell the left hand to move. But the cortex appeared to be ignoring the parts of the brain it normally communicates with in controlling movement. Instead, it acted more in sync than usual with a different brain region called the precuneus. The precuneus is involved in mental imagery and memory about oneself. The study suggests it was brimming with metaphors that participants heard from the hypnotist, such as: your hand is very heavy, it is stuck on the table, etcetera. So, it might have been telling the motor cortex, ‘Oh, but your hand is too heavy, you can’t move your hand.’ It’s as if the motor cortex is connected to the idea that it cannot move (the hand) and so it doesn’t send the message to move.