Temporal pattern analysis of somatosensory information encoded in the spike trains from the cutaneous nerve fibers

Abstract

Some people with amputated limbs can benefit from neural prosthetics to restore tactile sensation through electrical stimulation of the afferent nerve. The temporal spike train pattern generated in a healthy subject’s nerve by various types of somatosensation could provide key information to more closely mimic natural sensations using electrical stimulation. However, the temporal firing patterns of peripheral sensory fibers have not been well understood yet. To interpret somatosensory spike trains, ex-vivo single-fiber recordings was performed from the saphenous nerve in isolated skin-nerve preparations from mice. First, a notion that sensations are carried in the temporal pattern is demonstrated by categorizing the spike trains of the single primary afferent C-fibers by different chemical stimuli (KCl, GABA, and capsaicin) in Experiment I. These temporal patterns of the C-fibers for chemical stimuli were analyzed using a computational model based on consecutive spikes (N-cons), which were classified into three groups of responses. As C-fibers could be activated by hot, cold, and itching stimuli, stimulus-specific firing patterns were observed. In Experiment II, each unit responses to the chemical stimuli, i.e. capsaicin (hot), allyl-isothiocyanate (cold), and α-methyl-serotonin (itching) showed different spike trains from different groups. Additionally, spike trains for KCl, GABA, and capsaicin were reproduced based on triplet templates. The reproduced patterns were classified with significant accuracy into original templates of real spike trains. Therefore, these findings indicate that various somatosensory information, not only tactile, can be decoded and used as an input for computerized system. The N-cons approach to the analysis of temporal patterns of spike trains in C-fibers contributes a valuable insight to the interface for temporal profiles of various biological conditions.