Changes in the cutaneous silent period by paired stimulation

Abstract

The cutaneous silent period (CSP) corresponds to the inhibition of motor neuronal activity that is induced by electrical cutaneous stimulation. This motor neuronal inhibition might be useful as a therapeutic strategy for modulating the excitability of motor neurons. Therefore, we investigated the CSP changes that can be observed using the paired-stimulation method. Fifteen healthy adults were recruited. The digital cutaneous nerve of the right index finger was stimulated, and the CSP was recorded at the right thenar muscle. During the stimulation, contraction of the opposing right thumb and third finger was maintained at 20% of maximal voluntary contraction. A single stimulation was applied at the right index finger, and the duration and latency of the CSP (CSP1) was recorded. Paired electrical stimulations were then delivered with 60-, 80-, 100-, 120-, 140-, 160-, 180-, and 200-ms interstimulus intervals (ISI), and the latency and duration of a second CSP (CSP2) was measured and compared with that for the single stimulation. The CSP2 onset latencies were delayed in the 60-, 80-, and 100-ms ISI when compared to CSP1. CSP2 durations were shorter in the 60-, 80-, and 100-ms ISI. No significant differences in the latencies and durations between CSP1 and CSP2 were observed for ISI durations greater than 120 ms. We found that repetitive electrical stimulation changed the latency and duration of the CSP. These results suggest that the refractory period of the spinal inhibitory circuit in CSP is less than 100 ms.