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. 2019 Apr:36:100639.
doi: 10.1016/j.dcn.2019.100639. Epub 2019 Mar 19.

Infants discriminate the source of social touch at stroking speeds eliciting maximal firing rates in CT-fibers

Marie Aguirre  1 , Auriane Couderc  1 , Justine Epinat-Duclos  1 , Olivier Mascaro  2
Affiliations

Infants discriminate the source of social touch at stroking speeds eliciting maximal firing rates in CT-fibers

Marie Aguirre et al. Dev Cogn Neurosci. 2019 Apr.

Abstract

The evaluation of interpersonal touch is heavily influenced by its source. For example, a gentle stroke from a loved one is generally more pleasant than the same tactile stimulation from a complete stranger. Our study tested the early ontogenetic roots of humans' sensitivity to the source of interpersonal touch. We measured the heart rate of three groups of nine-month-olds while their legs were stroked with a brush. The participants were stroked at a different speed in each group (0.3 cm/s, 3 cm/s, 30 cm/s). Depending on the Identity condition (stranger vs. parent), the person who acted as if she was stroking the infant's leg was either an unfamiliar experimenter or the participant's caregiver. In fact, the stimulation was always delivered by a second experimenter blind to the Identity condition. Infants' heart rate decreased more in reaction to strokes when their caregiver rather than a stranger acted as the source of the touch. This effect was found only for tactile stimulations whose velocity (3 cm/s) is known to elicit maximal mean firing rates in a class of afferents named C-tactile fibers (CTs). Thus, the infants' reaction to touch is modulated not just by its mechanical properties but also by its social source.

Keywords: CT fibers; Caregiving; Infancy research; Social cognition; Social grooming; Touch.

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Figures

Fig. 1
Fig. 1
Panel A: Schematic representation of the spatial position and orientation of the participants. Each box represents a participant: either the subject (infant), the unfamiliar experimenter (E2) or the parent, and the experimenter stroking the infant’s leg (E3). A tablet displayed videos during the experiment, a plastic tray prevented infants from seeing who stroked their legs and a curtain separated the room in two parts, and allowed E3 to remain hidden from the infant’s viewpoint. Panels B and C: Pictures of the real set up. The adult is positioning the paintbrush next to the participants’ right leg, without touching the leg (brush-down position).
Fig. 2
Fig. 2
Mean ratio of signal change in heart rate from baseline to test (SEM) for all stroking velocity condition (slow, CT-optimal and fast). *: p <  0.05.
See this image and copyright information in PMC

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