Behavioral and Cortical Correlates of Self-Suppression, Anticipation, and Ambivalence in Rat Tickling. Shimpei Ishiyama, Lena V. Kaufmann, Michael Brecht. Current Biology, September 26 2019. https://doi.org/10.1016/j.cub.2019.07.085
Highlights
• Self-touch suppresses vocalizations and cortical excitation
• Self-touch suppression is rescued by blocking cortical inhibition
• Rats show ambivalent response to tickling
• Layer 5 somatosensory cortex represents tickle anticipation
Summary: The relationship between tickling, sensation, and laughter is complex. Tickling or its mere anticipation makes us laugh, but not when we self-tickle. We previously showed rat somatosensory cortex drives tickling-evoked vocalizations and now investigated self-tickle suppression and tickle anticipation. We recorded somatosensory cortex activity while tickling and touching rats and while rats touched themselves. Allo-touch and tickling evoked somatotopic cortical excitation and vocalizations. Self-touch induced wide-ranging inhibition and vocalization suppression. Self-touch also suppressed vocalizations and cortical responses evoked by allo-touch or cortical microstimulation. We suggest a global-inhibition model of self-tickle suppression, which operates without the classically assumed self versus other distinction. Consistent with this inhibition hypothesis, blocking cortical inhibition with gabazine abolished self-tickle suppression. We studied anticipation in a nose-poke-for-tickling paradigm. Although rats nose poked for tickling, they also showed escaping, freezing, and alarm calls. Such ambivalence (“Nervenkitzel”) resembles tickle behaviors in children. We conclude that self-touch-induced GABAergic cortical inhibition prevents self-tickle, whereas anticipatory layer 5 activity drives anticipatory laughter.
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