Short Latency Median Nerve Somatosensory Evoked Magnetic Fields and Electrical Potentials

Abstract

Short latency somatosensory evoked potentials recorded with median nerve stimulation at the wrist have been widely used to assess pathology affecting the sensory pathways. The generator sites for some response components have been well established (P30) but there is still disagreement about others (Nl9, P22,N40). The corresponding somatosensory evoked magnetic fields are particularly suited to the study of cortical generator sites. Transient response studies to slow rates of median nerve stimulation have concentrated on peaks from 30 to 200 ms(1,2). Several wave components have been identified and attributed to sources in the primary and secondary sensory cortical areas SI and SII (3,4,5). Only a small number of studies have specifically examined short latency responses (6,7,8) and the results have been inconclusive. In this study we aimed to examine the early somatosensory magnetic equivalents to the electrical N19, P22, P30 and N40, assess the reproducibility of the findings and suggest potential sources for these signals.