EFFECTS OF TRANSCUTANEOUS SPINAL RANDOM NOISE STIMULATION ON SENSORY FUNCTION IN HUMANS

Transcutaneous spinal random noise stimulation (tsRNS) may modulate afferent input and somatosensory processing, yet its effects on sensory function remain unclear. This study aimed to clarify the effects of tsRNS on tactile discrimination performance and somatosensory-evoked potentials (SEPs). Twenty healthy adults participated in a randomized, double-blind, sham-controlled crossover study. Participants underwent two conditions: 20 minutes of stimulation (real tsRNS) and 0.5 minutes of stimulation (sham tsRNS). tsRNS was applied through a pair of rubber electrodes placed on the anterior part of the neck and the spinous process of C6–T1, with a maximum current of 3 mA. Tactile discrimination performance was evaluated before, during, and after stimulation using the Semmes–Weinstein Monofilament (SWM) and two-point discrimination (2PD) tests at the hand and foot. SEPs were recorded following electrical stimulation of the right ulnar nerve, and the peak-to-peak amplitude of N20/P25 was evaluated. Additionally, paired-pulse SEP suppression with interstimulus interval of 40 ms were evaluated to investigate inhibitory mechanisms in S1. Both SWM and 2PD thresholds in the hand were significantly reduced during real tsRNS, but returned to baseline levels after the intervention. No significant changes were observed in the sham tsRNS or in foot assessments. The real tsRNS significantly increased N20/P25 amplitude and reduced paired-pulse SEP suppression, whereas no changes were observed in the sham tsRNS. These findings suggest that tsRNS immediately enhances tactile discrimination performance via stochastic resonance, while inducing an after effect that increases cortical excitability in S1.