The afferent origin of the secondary somatosensory evoked potential from the lower limb in humans

The afferent origin of the secondary somatosensory evoked potential elicited from stimulation of the sural and tibial nerves was investigated as the limb was cooled. It was hypothesized that the peak of this potential is initiated from primary afferents in the A alpha group. We conclude that the peak of the secondary SEP arises from an afferent source whose diameter is of similar size to that of large diameter A alpha afferents.