SPINAL CIRCUITS SPATIALLY ENCODE RESPONSES TO SKIN IRRITANTS

Reflexive skin twitches are a stereotypical behaviour used by mammals to dislodge a noxious stimulus. The neural circuits controlling this behaviour are thought to lie in the spinal cord, with motor neurons of the cutaneous maximus (CM) that trigger the twitches positioned in the lower cervical spinal cord. The spatial matching of the motor output to the location of the sensory stimulus points to selective innervation of particular CM motor neurons by specific sensory-responsive circuits in a spatially-dependent manner. Using mouse genetics and viral tracing, we show that a subset of dorso-lateral dI3 neurons form ascending projections onto motor neurons mediating skin twitches. These circuits are somatotopically organized to encode spatial information along the rostro-caudal and the medio-lateral axis. Furthermore, the direct optogenetic stimulation of dI3 ascending projections is sufficient to induce skin twitches in vivo. Together, we demonstrate the circuit basis of a spinal sensory representation of the torso that participate to the removal of irritants such as insects.