Selective temporal shift in the somatosensory evoked potential produced by chronic stimulation of the human index finger.

The present study determined whether the cortical potential from the human index finger changed with chronic nerve stimulation. Cerebral potentials were repeatedly recorded to stimulation of the ulnar nerve and the digital nerves of thumb, index and middle fingers, before and during a 7-day period in which the index was electrically stimulated (80 Hz) for 8-10 h daily. Cerebral potentials were recorded at three scalp sites over the contralateral "hand" area. Chronic stimulation produced no significant changes in the amplitudes or distribution of the cerebral potentials from the individual digits or the ulnar nerve. However, for the stimulated index finger there was a significant, progressive increase in latency of N20 and P25 without a detectable change in conduction velocity of distal peripheral axons. Timing in human central somatosensory pathways may be altered by the previous pattern of peripheral nerve inputs.