I love when a bunch of papers come flying out together, or else sequentially but close enough together that they seem related, that all seem to relate favourably to human primate social grooming.
Here they are:
Hao Wu, John Williams, Jeremy Nathans; Morphologic diversity of cutaneous sensory afferents revealed by genetically directed sparse labeling. eLife 2012;1:e00181 (Written about here)
Vrontou, S. et al. Genetic identification of C fibres that detect massage-like stroking of hairy skin in vivo. Nature 493, 669–673 (2013) (abstract only)
Tajerian M, Alvarado S, Millecamps M, Vachon P, Crosby C, et al. (2013) Peripheral Nerve Injury Is Associated with Chronic, Reversible Changes in Global DNA Methylation in the Mouse Prefrontal Cortex. PLoS ONE 8(1): e55259. (Open access)
What do all these papers say?
The first one has mapped the surface of skin. In rats.. but still. Surface of skin. Humans have surface of skin too. Probably we still have pretty axons trailing around, even though we lost most of our fur long ago. Whatever, we still have lots of Ruffini endings in any case. They'll do.
The second one is just the latest in a string of papers, going back years, about how there are afferent neurons that specifically code for pleasurable sensation.
The third one actually tries to measure what goes up in the brain in peripheral nerve injury (code for nociceptive input/neuropathic "pain" in a mouse model), and how it can be reversed "environmentally" - which is to say, from "outside" the organism, by environmental "enrichment." Which likely involved more pleasurable distraction, interaction with other mice (including contact), and more movement in general. Although the authors didn't say that specifically.