Temporal Analysis of Cortical Mechanisms for Pain Relief by Tactile Stimuli in Humans

Abstract

The mechanisms by which vibrotactile stimuli relieve pain are not well understood, especially in humans. We recorded cortical magnetic responses to paired noxious (intra-epidermal electrical stimulation, IES) and innocuous (transcutaneous electrical stimulation, TS) stimuli applied to the back at a conditioning-test interval (CTI) of -500 to 500 ms. Results showed that IES-induced responses were remarkably attenuated when TS was applied 20-60 ms later and 0-500 ms earlier than IES (CTI = -60 to 500 ms). Since the signals evoked by IES reached the spinal cord (CTI = -60 to -20 ms conditions) and the cortex (-60 and -40 ms condition) earlier than those evoked by TS, the present results indicate that cortical responses to noxious stimuli can be inhibited by innocuous tactile stimuli at the cortical level, with minimal contribution at the spinal level.

C-tactile afferents: Cutaneous mediators of oxytocin release during affiliative tactile interactions?

“…Studies in animal models and in humans have focused primarily on spinal and supra spinal mechanisms respectively (Inui et al, 2006;Salter and Henry, 1990). Recently, Mancini et al (2015) reported that a tactile stimulus significantly reduced both early Aδ and late C-fibre evoked potentials.…”

Static mechanical allodynia (SMA) is a paradoxical painful hypo-aesthesia: Observations derived from neuropathic pain patients treated with somatosensory rehabilitation

“…The ''gate control'' theory has provided a possible mechanism contributing to this phenomenon (Melzack and Wall 1965), with the hypothesis that influences of large myelinated inputs inhibit the central transmission of signals conveyed by nociceptors, occurring in the dorsal horn of the spinal cord. Based on the precise timing of activities generated in these two separate systems of afferent fibres, a recent work suggested that such inhibition is more likely to occur at cortical than spinal level (Inui et al 2006). In line with this observation, another study using psychophysical and physiological measures in humans concluded that the inhibition by large diameter fibres takes place at supraspinal level (Nahra and Plaghki 2003).…”

“…This observation indicates that, even if the central sensitization has been established for a long time, it can still be reversed, at least enough to eliminate the evoked and spontaneous pains. The mechanisms underlying the reversal of central sensitization, in particular how vibrotactile stimuli may relieve pain, are largely unknown (Inui et al 2006). The ''gate control'' theory has provided a possible mechanism contributing to this phenomenon (Melzack and Wall 1965), with the hypothesis that influences of large myelinated inputs inhibit the central transmission of signals conveyed by nociceptors, occurring in the dorsal horn of the spinal cord.…”

Selective Stimulation of C Fibers by an Intra-Epidermal Needle Electrode in Humans

“…We have developed a method of intra-epidermal electrical stimulation (IES) for the selective activation of A *Address correspondence to this author at the Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan; Tel: +81 564 55 7811; Fax: +81 564 52 7913; E-mail: ootsuru@nips.ac.jp fibers [11][12][13][14][15][16]. Since this method is easy to control, does not require special equipment, and provides a steep rise of stimulation, it would be good for studying the C fiber nociceptive system if it could activate C fibers selectively.…”