For the cutting-edge experiment, a collaboration between the University of Pittsburgh and the University of Pittsburgh Medical Center, electrodes smaller than a grain of sand were implanted in the sensory cortex of the man's brain. The electrodes received signals from a robot arm. When a researcher pressed the fingers of the prosthesis, the man felt the pressure in the fingers of his paralyzed right hand, effectively bypassing his damaged spinal cord

The results of the experiment, which have been repeated over several months with 30-year-old Nathan Copeland, offer a breakthrough in the restoration of a critical function in people with paralyzed limbs: the ability not just to move those limbs, but to feel them.