The interface depends on the brain maintaining for many years the circuits once used to move an arm, hand, or leg. Earlier studies had suggested that after the loss of a hand, the brain would shift the borders of its body map. Many of these interfaces place electrodes in the same area of the brain that maintains the body map. HAMILTON: Schone says earlier studies were limited because they compared the brains of people who’d lost a limb with the brains of typical people. HAMILTON: For example, a prosthetic arm connected to the same brain map once used for a natural arm.