The nerve endings in our skin that respond to soft stroking also send signals to the brain to arouse sexual desire under the right circumstances, according to studies in mice and people.
Previous research shows that gentle touch feels good because it stimulates nerve receptors in the skin called C-tactile afferents. These respond to soft, slow stroking, and send signals to brain regions involved in emotion and pleasure.
Gentle touch has been shown to play a role in numerous social relationships, including between parents and children. For example, babies鈥� heart rates slow when their parents gently stroke their forearms or shins with soft paintbrushes, suggesting they find it comforting.
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Now, at Columbia University in New York and his colleagues have shown that these nerves may also kindle sexual desire when partners touch.
They genetically engineered mice so that nerves in their skin that behave like human C-tactile afferents could be activated by shining blue light on them, rather than by physically touching them.
When they used blue light to artificially activate these nerves, they found that females arched their backs in a similar way to when they were preparing for sex. The mice also experienced a rush of dopamine in their nucleus accumbens, a pleasure centre in the brain.
Female mice engineered to lack these nerves didn鈥檛 get the same dopamine rush when males tried to mount them for sex, and instead turned aggressive and tried to fight them off. This hints that these nerves convey messages to the brain to 鈥渆ncode a sensation that is necessary for the rewarding nature of sexual touch鈥�, write the authors.
Read more: Why your brain needs touch to make you human
鈥淚t鈥檚 a fantastic study,鈥� says at Link枚ping University in Sweden, who was one of the first to discover C-tactile afferents in human skin in the 1990s. 鈥淲e don鈥檛 understand much at all about the neural mechanisms of sexual behaviour, so this is an important finding.鈥�
More research will be needed to confirm that the same skin-to-brain circuit is involved in human sexual arousal, but there are emerging clues, says Olausson. For example, people report feeling erotic sensations when their forearms, inner thighs, necks and foreheads are softly stroked at speeds known to stimulate C-tactile nerves in the skin. Conversely, people who undergo surgery that damages C-tactile nerves are no longer able to experience erotic sensations when their skin is touched.
Other research shows that a type of sex therapy called sensate focus, in which couples explore touching each other鈥檚 bodies without intercourse, is useful for treating low sexual desire and erectile dysfunction.
But it is important to note that stimulation of C-tactile nerves only activates sexual desire in certain contexts, says Olausson. Our brains use other cues to interpret signals from these nerves, so that being touched by a lover has different effects to being touched by a friend, for instance.
Touch may also be sensed as more erotic when couples first get together, whereas it may signal security and comfort in more established couples, says Olausson. 鈥淏ut we don鈥檛 know how these top-down processes in the brain work yet,鈥� he says.
搁别蹿别谤别苍肠别:听bioRxiv,
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