Most notably in their mouse studies, they for the first time teased out a full pathway that begins with neurons in the skin that respond to gentle stroking and run all of the way to pleasure centers of the brain.

Scientists have long known the skin features tactile sensory cells–key components of the peripheral nervous system–that enable us to discern different textures and temperatures, as well as varieties of pleasurable and painful mechanical stimuli.

Crisp as this result was, the new data led to a compelling but daunting research question: how do these peripheral cells link into downstream neural circuitry through the spinal cord and then more centrally into the brain?

Credit: Abdus-Saboor Lab/Zuckerman Institute​​​​​​​One major finding is that the brainstem neurons the Harvard-led team studied linked to yet deeper locations in the brain, the ventral tegmental area as well as the nucleus accumbens.

Even in social isolation, optogenetic stimulation of Mrgprb4-lineage neurons through the back skin is sufficient to induce a conditioned place preference and a striking dorsiflexion resembling the lordotic copulatory posture.

In the absence of Mrgprb4-lineage neurons, female mice no longer find male mounts rewarding: sexual receptivity is supplanted by aggression and a coincident decline in dopamine release in the nucleus accumbens.