Discrimination of phantom hand sensations elicited by afferent electrical nerve stimulation in below-elbow amputees.

The necessity for a sensory feedback system that would enhance patient acceptability of motorized hand prostheses is now generally acknowledged. Afferent electrical stimulation of the nerves in the amputation stump can convey sensory feedback from prostheses with the advantage of eliciting sensations in the phantom image of the lost hand. Experiments with percutaneous nerve stimulation of the amputation stump in below-elbow amputees showed that with stable electrode conditions, amplitude modulated stimulation was better than frequency modulated stimulation in terms of accuracy, delay, and transinformation both with intermittent and uninterrupted stimulation. With unstable electrode conditions, different results were noticed, since amplitude modulated stimulation is very sensitive even to minor changes in electrode position. It is concluded that afferent electrical nerve stimulation with adequate training and stable electrodes had characteristics of accuracy, transinformation and delay which are good enough to make it a suitable method of conveying information in a prosthesis feedback system.