Skin type and nerve effects on cortical tactile processing: a somatosensory evoked potentials study.

Abstract

Somatosensory evoked potentials (SEP) studies typically characterize short latency components following median nerve stimulations of the wrist. However, these studies rarely considered 1) skin type (glabrous/hairy) at the stimulation site, 2) nerve being stimulated, and 3) middle latency (>30 ms) components. Our aim was to investigate middle latency SEPs following simple mechanical stimulation of two skin types innervated by two different nerves. 18 adults received 400 mechanical stimulations over four territories of the right hand (two nerves: radial/median; two skin types: hairy/glabrous skin) while their EEG was recorded. Four middle latency components were identified: P50, N80, N130 and P200. As expected, significantly shorter latencies and larger amplitudes were found over the contralateral hemisphere for all components. A skin type effect was found for the N80: glabrous skin stimulations induced larger amplitude than hairy skin stimulations. Regarding nerve effects, median stimulations induced larger P50 and N80. Latency of the N80 was longer after median nerve stimulation compared to radial nerve stimulation. This study showed that skin type and stimulated nerve influence middle latency SEPs, highlighting the importance of considering these parameters in future studies. These modulations could reflect differences in cutaneous receptors and somatotopy. Middle latency SEPs can be used to evaluate the different steps of tactile information cortical processing. Modulation of SEPs components before 100 milliseconds possibly reflects somatotopy and differential processing in SI cortex.