Neural correlates of ticklishness in the rat somatosensory cortex.

Rats emit ultrasonic vocalizations in response to tickling by humans. Tickling is rewarding through dopaminergic mechanisms, but the function and neural correlates of ticklishness are unknown. We confirmed that tickling of rats evoked vocalizations, approach, and unsolicited jumps (Freudensprünge). Recordings in the trunk region of the rat somatosensory cortex showed intense tickling-evoked activity in most neurons, whereas a minority of cells were suppressed by tickling. Tickling responses predicted nontactile neural responses to play behaviors, which suggests a neuronal link between tickling and play. Anxiogenic conditions suppressed tickling-evoked vocalizations and trunk cortex activity. Deep-layer trunk cortex neurons discharged during vocalizations, and deep-layer microstimulation evoked vocalizations. Our findings provide evidence for deep-layer trunk cortex activity as a neural correlate of ticklishness.