Mancini, F;
Beaumont, AL;
Hu, L;
Haggard, P;
Iannetti, GDD;
(2015)
Touch inhibits subcortical and cortical nociceptive responses.
Pain
, 156
(10)
pp. 1936-1944.
10.1097/j.pain.0000000000000253.
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Abstract
The neural mechanisms of the powerful analgesia induced by touching a painful body part are controversial. A long tradition of neurophysiological studies in anaesthetized, spinal animals indicate that touch can gate nociceptive input at spinal level. In contrast, recent studies in awake humans have suggested that supra-spinal mechanisms can be sufficient to drive touch-induced analgesia. To investigate this issue, we evaluated the modulation exerted by touch on established electrophysiological markers of nociceptive function at both subcortical and cortical levels in humans. Aδ and C skin nociceptors were selectively activated by high-power laser pulses. As markers of subcortical and cortical function, we recorded the Laser-Blink Reflex (LBR), which is generated by brainstem circuits prior to the arrival of nociceptive signals at the cortex, and Laser-Evoked Potentials (LEPs), which reflect neural activity of a wide array of cortical areas. If subcortical nociceptive responses are inhibited by concomitant touch, supraspinal mechanisms alone are unlikely to be sufficient to drive touch-induced analgesia. Touch induced a clear analgesic effect, suppressed the LBR, and inhibited both Aδ-fibre and C-fibre LEPs. Thus, we conclude that touch induced-analgesia is likely to be mediated by a subcortical gating of the ascending nociceptive input, which in turn results in a modulation of cortical responses. Hence, supra-spinal mechanisms alone are not sufficient to mediate touch-induced analgesia.
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