Affective CT-touch attenuates cortical responses and subjective attention during temporal summation of second pain

Abstract

The activation of C-tactile (CT) mechanoreceptors is typically experienced as pleasant touch and has been proposed to have analgesic effects. However, its influence on central sensitization across social and non-social contexts remains unclear. We investigated whether CT-touch in social (romantic partner) and non-social (robotic arm) contexts influences the development of temporal summation of second pain (TSSP), a paradigm associated with central sensitization. Thirty-two couples completed a TSSP protocol across four conditions in two sessions: dyadic session (TSSP during CT-optimal stroking or static touch by the participant's romantic partner) and individual session (TSSP during robotic CT-touch or vibration). Outcomes included subjective pain ratings, attention to heat stimuli, pleasantness, electroencephalographic activity (N2-P2 event-related potentials and midfrontal theta activity), autonomic responses and sex-related effects. No condition differences were found in the reported pain increase. Attention to painful heat was lower during partner's stroking and higher during vibration, the least pleasant stimulus. At the neural level, the smallest N2-P2 amplitudes occurred during partner's stroking, followed by static touch, robot brushing and vibration. Reduced midfrontal theta activity was observed in dyadic compared to individual contexts. No differences emerged in autonomic indices or sex comparisons. Using a large sample and naturalistic stimuli, we found that affective CT-touch does not affect pain levels or autonomic activity during TSSP, yet it decreases attentional focus on the nociceptive input and associated neural responses. These findings underscore social-affective touch as a naturalistic mechanism for modulating pain salience, raising new questions about how it shapes neural dynamics of pain regulation. KEY POINTS: Affective C-tactile (CT) touch has no effect on temporal summation of second pain. Social context matters: partner-administered CT-touch reduced attention to nociceptive heat and attenuated N2-P2 event-related potentials compared with robotic or vibration stimuli. Midfrontal theta activity was lower in dyadic (social) vs. individual (non-social) contexts, suggesting neural markers of pain salience are context-dependent. Findings highlight social-affective touch as a naturalistic mechanism for modulating the salience of painful stimuli, offering insights into pain regulation and the neural dynamics of central sensitization.