Research paperA positive touch: C-tactile afferent targeted skin stimulation carries an appetitive motivational value

- C-tactile afferents (CTs) are unmyelinated low threshold mechanosensitive C-fibres found in the hairy skin of mammals.
- They are hypothesised to signal the rewarding value of social tactile interactions.
- Here we provide implicit empirical support for this Social Touch Hypothesis.
- We show C-tactile afferent targeted skin stimulation carries an appetitive motivational value.
- Through evaluative conditioning this appetitive value can be passed to previously neutral socially relevant stimuli.

The rewarding sensation of touch in affiliative interactions is hypothesised to be underpinned by an unmyelinated system of nerve fibres called C-tactile afferents (CTs). CTs are velocity tuned, responding optimally to slow, gentle touch, typical of a caress. Here we used evaluative conditioning to examine whether CT activation carries a positive affective value. A set of neutral faces were paired with robotically delivered touch to the forearm. With half the faces touch was delivered at a CT optimal velocity of 3 cm/s (CT touch) and with the other half at a faster, non-CT optimal velocity of 30 cm/s (Control touch). Heart-rate and skin conductance responses (SCRs) were recorded throughout. Whilst rated equally approachable pre-conditioning, post-conditioning faces paired with CT touch were judged significantly more approachable than those paired with Control touch. CT touch also elicited significantly greater heart-rate deceleration and lower amplitude SCRs than Control touch. The results indicate CT touch carries a positive affective value, which can be acquired by socially relevant stimuli it is associated with.