Conduction time in central somatosensory pathways in man.

Simultaneous recording of the somatosensory evoked potential (SEP) from the neck and from the scalp allows investigation of conduction of somatosensory impulses within the central nervous system alone. The early components of the SEP produced by stimulation of the median nerve at the wrist were recorded from standardized electrode locations on the scalp and neck in 21 normal subjects. The peak latency of both the initial negative potential from the scalp, N20 (19.4 +/- 1.1 msec), and the major negative negative potential from the neck, N14 (13.8 +/- 0.9 MSEC), CORRElated positively with arm length and with height. The difference between the peak latencies of N20 and N14 (5.6 +/- 0.5 msec) was independent of both arm length and height. As the latency and distribution of N14 indicate that this potential probably arises from the dorsal column nuclei, the N20--N14 latency difference provides a measure of conduction time within central pathways which is independent of conduction time in the limbs and spinal cord. Recording of the SEP from the neck, simultaneously with that from the scalp, also facilitates clinical investigation of the somatosensory system.