C-tactile afferents: Cutaneous mediators of oxytocin release during affiliative tactile interactions?
Low intensity, non-noxious, stimulation of cutaneous somatosensory nerves has been shown to trigger oxytocin release and is associated with increased social motivation, plus reduced physiological and behavioural reactivity to stressors. However, to date, little attention has been paid to the specific nature of the mechanosensory nerves which mediate these effects. In recent years, the neuroscientific study of human skin nerves (microneurography studies on single peripheral nerve fibres) has led to the identification and characterisation of a class of touch sensitive nerve fibres named C-tactile afferents. Neither itch nor pain receptive, these unmyelinated, low threshold mechanoreceptors, found only in hairy skin, respond optimally to low force/velocity stroking touch. Notably, the speed of stroking which C-tactile afferents fire most strongly to is also that which people perceive to be most pleasant. The social touch hypothesis posits that this system of nerves has evolved in mammals to signal the rewarding value of physical contact in nurturing and social interactions. In support of this hypothesis, we review the evidence that cutaneous stimulation directly targeted to optimally activate C-tactile afferents reduces physiological arousal, carries a positive affective value and, under healthy conditions, inhibits responses to painful stimuli. These effects mirror those, we also review, which have been reported following endogenous release and exogenous administration of oxytocin. Taken together this suggests C-tactile afferent stimulation may mediate oxytocin release during affiliative tactile interactions.
Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK.. Electronic address: s.c.walker@ljmu.ac.uk.
Susannah C
SC
Walker
Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK.
Paula D
PD
Trotter
Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK.
William T
WT
Swaney
Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK.; Department of Clinical Neurophysiology, Salford Royal NHS Foundation Trust, Salford M6 8HD, UK.
Andrew
A
Marshall
Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK.; Institute of Psychology, Health and Society, University of Liverpool, UK.
Francis P
FP
Mcglone
D000818:Animals; D004644:Emotions / Q000502:physiology*; D006801:Humans; D036421:Nerve Fibers, Unmyelinated / Q000378:metabolism; D010121:Oxytocin / Q000378:metabolism*; D010812:Physical Stimulation / Q000379:methods; D012867:Skin / Q000294:innervation / Q000378:metabolism*; D012919:Social Behavior
D010121:Oxytocin
C-fibre; C-tactile afferent; Oxytocin; Pain; Pleasant touch; Social