The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science

by Norman Doidge

When Ramachandran reviewed the histories of people with painful frozen arms, he discovered that they had all had their arms in slings or casts for several months before amputation. Their brain maps now seemed to record, for all time, the fixed position of the arm just prior to amputation. He began to suspect that it was the very fact that the limb did not exist that allowed the sensation of paralysis to persist. Normally, when the motor command center in the brain sends out an order to move the arm, the brain gets feedback from various senses, confirming that the order has been executed. But the brain of a person without a limb never gets confirmation that the arm has moved, since there are neither arm nor motion sensors in the arm to provide that feedback. Thus, the brain is left with the impression that the arm is frozen. Because the arm had been stuck in a cast or sling for months, the brain map developed a representation of the arm as unmoving. When the arm was removed, there was no new input to alter the brain map, so the mental representation of the limb as fixed became frozen in time—a situation similar to the learned paralysis that Taub discovered in stroke patients.