EFFECT OF MOTOR CORTEX FEEDBACK ON MOUSE WHISKER SENSORY PROCESSING IN PRIMARY SOMATOSENSORY CORTEX

In the mouse somatosensory cortex (S1), whisker touch evokes an early and late response that travel horizontally across the cortex resembling a traveling wave. Traveling waves have been shown to be a key aspect of neural processing, and previous work has indicated the late traveling wave is reliant on long range feedback from motor cortex (MC). How these traveling waves change under a goal directed behavior and what effect MC feedback has on S1 neural processing is still unclear. To investigate the effect of MC feedback on traveling wave dynamics and neuronal spiking in S1, we inhibited MC inputs to S1 using optogenetics while recording with micro-ECoG arrays or silicon probes in S1. Under passive whisker stimulation, we observed a significant decrease in wave amplitude, wave speed, and multi-unit activity during the late period (~100ms after the deflection), accompanied with desynchronization of sensory-evoked populational response. This suggests organized and sustained S1 activity is supported by MC inputs. Interestingly, the MC-inhibition was accompanied with increased spiking in deep cortical layers, suggesting MC feedback onto S1 also has an inhibitory role. In animals performing an active whisker-based sensory discrimination task, we observed a decrease in touch evoked wave speed for reward vs non-reward whisker touches. Interestingly, inhibition of MC inputs during active touch showed an increase in spontaneous and touch evoked wave speed of both reward-associated and unassociated whiskers. This indicates MC influence on S1 traveling waves is brain state dependent. Together, our work suggests that MC feedback is critical in organizing S1 neural activity during sensory processing, potentially through regulating local excitation/inhibition balance to enable optimal neural coding.