Interareal synaptic inputs underlying whisking-related activity in the primary somatosensory barrel cortex

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Body movements, especially orofacial movements, are known to influence brain-wide neuronal activity. In the sensory cortex, thalamocortical bottom-up inputs and motor-sensory top-down inputs are thought to affect the dynamics of membrane potentials (V m ) of neurons and change their processing of sensory information during movements. However, direct perturbation of the axons projecting to the sensory cortex from other remote areas during movements has remained unassessed, and therefore the interareal circuits generating motor-related signals in sensory cortices are still unclear. Using a G i -coupled opsin, eOPN3, we here inhibited interareal signals incoming to the whisker primary somatosensory cortex (wS1) of awake behaving mice and tested their effects on whisking-related changes in neuronal activities in wS1. Spontaneous whisking in air induced the changes in spike rates of a fraction of wS1 neurons which were accompanied by depolarization and substantial reduction of slow-wave oscillatory fluctuations of V m . Despite an extensive innervation, inhibition of inputs from the whisker primary motor cortex (wM1) to wS1 did not alter the spike rates and V m dynamics of wS1 neurons during whisking. In contrast, inhibition of axons from the whisker-related thalamus (wTLM) and the whisker secondary somatosensory cortex (wS2) to wS1 largely attenuated the whisking-related supra- and sub-threshold V m dynamics of wS1 neurons. Our findings thus suggest that sensorimotor integration in wS1 during spontaneous whisking is mediated by direct synaptic inputs from wTLM and wS2 rather than from wM1.

Significance statement

The traditional viewpoint underscores the importance of motor-sensory projections in shaping movement-induced neuronal activity within sensory cortices. However, this study challenges such established views. We reveal that the synaptic inputs from the whisker primary motor cortex do not alter the dynamics of neuronal activity in the whisker primary somatosensory cortex (wS1) during spontaneous whisker movements. Furthermore, we make a novel observation that inhibiting inputs from the whisker secondary somatosensory cortex (wS2) substantially curtails movement-related activities in wS1. These findings provoke a reconsideration of the role of motor-sensory projections in sensorimotor integration and bring to light a new function for wS2-to-wS1 projections.

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