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Published online: 5 February 2018
© Psychonomic Society, Inc. 2018
Abstract
Tactile interactions are of developmental importance to social and emotional interactions across species. In beginning to understand the affective component of tactile stimulation, research has begun to elucidate the neural mechanisms that underscore slow, affective touch. Here, we extended this emerging body of work and examined whether affective touch (C tactile [CT]-optimal speed), as compared to nonaffective touch (non-CT-optimal speed) and no touch conditions, modulated EEG oscillations. We report an attenuation in alpha and beta activity to affective and nonaffective touch relative to the no touch condition. Further, we found an attenuation in theta activity specific to the affective, as compared to the nonaffective touch and no touch conditions. Similar to theta, we also observed an attenuation of beta oscillations during the affective touch condition, although only in parietal scalp sites. Decreased activity in theta and parietal-beta ranges may reflect attentional-emotional regulatory mechanisms; however, future work is needed to provide insight into the potential neural coupling between theta and beta and their specific role in encoding slow, tactile stimulation.
Keywords Affective touch . CT fibers . EEG . Neural oscillations
Introduction
Caress-like, gentle touch is important for social communication and the formation of social bonds (Hertenstein, Keltner, App, Bulleit, & Jaskolka, 2006; Suvilehto, Glerean, Dunbar, Hari, & Nummenmaa, 2015). In rodents and primates, social gentle touch has long-term, stress-alleviating effects (Korosi & Baram, 2010) and reduces pain and separation distress (Agren, Lundeberg, Uvnäs-Moberg, & Sato, 1995; Nelson & Panksepp, 1998). Similarly, gentle touch has positive effects in humans. Early in development, gentle touch helps calm infant pain and discomfort (Field, 2010) and acts as an important regulator of an infant's arousal in early parental interactions (Hofer, 1994). In adulthood, findings suggest that slow, gentle touch modulates pain (Krahé, Drabek, Paloyelis, & Fotopoulou, 2016; Liljencrantz et al., 2017) and autonomic arousal (Pawling, Cannon, McGlone, & Walker, 2017), while carrying positive affective valence (e.g., Pawling et al., 2017; Perini, Olausson, & Morrison, 2015). Consistent with the social touch as a stress buffer hypothesis (Morrison, 2016), these lines of research suggest that gentle touch exerts an influence on affective regulatory functioning throughout the life span. Moreover, clinical work suggests that tactile-based interventions improve clinical outcomes, including...