Abstract
Affective touch plays a key role in affiliative behavior, offering a mechanism for the formation and maintenance of social bonds among conspecifics, both in humans and non-human primates. Furthermore, it has been speculated that the CT fiber system is a specific coding channel for affiliative touch that occurs during skin-to-skin interactions with conspecifics. In humans, this touch is commonly referred to as the caress, and its correlation with the CT fiber system has been widely demonstrated. It has been hypothesized that the sweeping touch that occurs during grooming in non-human primates may modulate the CT fibers, with recent preliminary studies on rhesus monkeys supporting this hypothesis. The present mini-review proposes a comparison between the pleasant touch, caress and sweeping of humans and non-human primates, respectively. The currently available data was therefore reviewed regarding (i) the correlation between pleasant touch and CT fibers both in humans and non-human primates, (ii) the autonomic effects, (iii) the encoding at the central nervous system, (iv) the development from early life to adulthood, and (v) the potential applications of pleasant touch in the daily lives of both humans and non-human primates. Moreover, by considering both the similarities and discrepancies between the human caress and non-human primate sweeping, a possible evolutionary mechanism can be proposed that has developed from sweeping as a utilitarian action with affiliative meaning among monkeys, to the caress as a purely affective gesture associated with humans.
Highlights
Specialty section: This article was submitted to Emotion Science, a section of the journal Frontiers in Psychology
FROM NON-HUMAN PRIMATES SWEEPING TO THE HUMAN CARESS
In non-human primates, despite many studies hypothesizing on the social role of grooming, it was proposed that the sweeping which occurs during grooming could be considered homologuous to the human affective touch (Morrisson et al, 2010), and that rather than grooming per se, this motion may modulate the CT fibers (Dunbar, 2010)
Summary
The sense of touch assumes a critical importance in daily life, since it enables the ability to discriminate and haptically explore and identify objects, with the optional integration of other sensory information (the sensory-discriminative aspect), but it allows us to communicate with others while creating and maintaining social bonds according to the emotional valence that touch assumes (the motivational-affective aspect). The static touch responsible for the discriminative aspect activates the large myelinated low threshold mechanoreceptors (LTMRs) to allow the rapid encoding of an object’s features at the central nervous system level. The affiliative touch activates the C tactile unmyelinated LTMRs (CT fibers), to instead allow the processing of the emotional meaning of the touch
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