Parallel inhibitory and excitatory sensorimotor loops control active sensing

Friday, August 4, 2017

The Wang lab, in collaboration with Martin Deschene’s lab, discovered parallel disynaptic sensory feedback circuits in the brainstem that control the movements of touch sensors. This work is published in August 2 issue of Neuron.

Mice and rats move their facial whiskers as touch sensors to explore environment in dark by actively sweeping the whiskers back and forth (whisking). Upon contact with an object, the whiskers on the contact side exhibit rapid reflexive movements: retraction (touch-induced retraction), or retraction followed by a brief protraction (touch-induced pump). The circuitry mediating such sensory feedback induced reflex was unknown previously.

Using intracellular recording in anesthetized rats as well as anatomical tracing, the Deschene lab found short latency inputs to whisker motoneurons from brainstem sensory nuclei that receive direct inputs from whisker sensory afferents. Postdoctoral fellow Jun Takatoh and graduate student Jinghao Lu in the Wang lab have been studying this problem by using intersectional viral genetic strategies to identify neurons mediating the reflexes, followed by using opto- and chemico-genetic tools to activate or silence these neurons in awake behaving mice.

The Deschene lab and the Wang lab joined forces and discovered three groups of premotor neurons that receive sensory afferents and project to different whisker motoneurons: a population of excitatory neurons that specifically innervate the motoneurons functioning to retract the whisker pad, thereby mediating touch-induced retraction; a second group of inhibitory neurons that selectively innervate the motoneurons functioning to protract the whiskers, thereby preventing further protraction upon contact; and a third group of excitatory neurons that project to both retraction and protraction motoneurons with a bias to protraction neurons. Combinatorial activities of these three groups of neurons formed a push-pull system to mediate the observed touch-induced retraction or touch-induced pump.  This study provides the precise circuit mechanism for rapid modulation of tactile sensors during environmental explorations.