Among the most devastating of disabilities are spinal injuries that sever communication between the brain and the limbs. The nerve cells in the brain devoted to controlling limb movement are still there, but unable to communicate with the limb muscles.
Recent amputees suffer the same disconcerting period of adjustment.
Many researchers have tried to find a way to put these motor nerve cells to work, reestablishing communication between them and disconnected or artificial limbs. If they knew what signal to send, then perhaps they could produce commands that a disconnected or prosthetic limb would understand and obey. This has proven very difficult to do, however. To intercept the signals that control limbs, researchers inserted a minute electrode into the brain, so that the electrode's tip touched a single cell in the motor cortex, the region of the brain that controls movement. Success, when it came, required a scientist able to step back from these largely unsuccessful experiments and ask the question a different way.