SINGLE-UNIT DISCRIMINATION AMONG DISCHARGES FROM NEIGHBORING MYELINATED FIBERS IN HUMAN PERIPHERAL-NERVES - IMPROVED UNIT IDENTIFICATION BYINTERSPIKE INTERVAL-ANALYSIS OF NERVE RESPONSES EVOKED BY TACTILE STIMULI

Clustered rapidly adapting (RA) or slowly adapting type I (SA I) units recorded with concentric needle electrodes from median nerves of heal thy human volunteers may exhibit overlapping receptive fields in the s kin as also Paccini afferents (PC units) and slowly adapting type II u nitary elements (SA II units) with their much larger innervation areas . Fundamental for the discrimination of such pairs of neighboring unit s in the nerve with overlapping peripheral fields was the refractory p eriod of the studied fibers, which was assumed to be normal, i.e., of the order of 1-2 ms. When a unit belonging to one of the categories me ntioned was found, it was activated by different tactile stimuli in th e palm or fingers. Simultaneously, interspike interval analysis of the evoked responses was performed. In situations when the minimal inters pike intervals were longer than the absolute refractory period of a si ngle fiber the response derived from one single unit. Responses from a t least two units were considered to contribute to the recorded sequen ces when computer analysis showed that the durations of the minimal in tervals were shorter. In this way, the reported procedure facilitated the discrimination of both pairs of RA and SA I units and, in particul ar, pairs of neighboring PC or SA II units with overlapping receptive fields in human palmar skin. (C) 1996 Academic Press, Inc.