Cutaneous silent periods - Part 1: Update on physiological mechanisms.

Testing of exteroceptive electromyographic modulation of ongoing voluntary muscle activity is of interest in normal human physiology and in diagnostic clinical neurophysiology in normal and pathological conditions. The cutaneous silent period (CSP) is a robust and reproducible nociceptive EMG suppression, mediated at the spinal level by small-diameter A-delta afferents. This critical review surveys the literature on applied stimulation and recording techniques, physiological principles, involved fiber types, spinal circuitry, supraspinal modulation, neurotransmitters and pharmacology of CSPs. Understanding the principles of CSP testing is fundamental for a valid and thoughtful clinical application of CSPs (reviewed in part 2) (Kofler et al., 2019).