Innocuous Peripheral Nerve Stimulation Shifts Stimulus–Response Function of Painful Laser Stimulation in Man

Abstract

Electrical peripheral nerve stimulation (PNS) is discussed as an effective neuromodulatory treatment in chronic pain. This human experimental study hypothesized a rightward shift of stimulus-response function as a marker of antinociceptive and analgesic PNS effects. Innocuous electrical PNS of the left superficial radial nerve trunk evoked paresthesia on the left hand dorsum in 29 healthy volunteers. In this innervation area, laser stimulation was performed before, during, and after PNS. Ten different laser intensities ranging between perception and tolerance thresholds were applied. Cortical laser-evoked potentials (LEP) were recorded, and perceptual ratings were documented. Data were analyzed in low, medium, and high laser intensity categories. Stimulus-response functions were calculated. Laser detection and pain thresholds were interpolated. Interpolated laser thresholds after logarithmic regression were not different from measured thresholds. Laser pain threshold increased during and after PNS. LEP amplitude decreased at medium and high intensities under PNS. Ratings transiently decreased during PNS at medium and high laser intensities. Modulation of laser pain threshold, perceptual ratings, and LEP indicates a rightward shift of stimulus-response function under PNS. These data emphasize antinociceptive and analgesic effects of PNS in an experimental human model and support its clinical neuromodulative relevance.