Postdoctoral Fellow, Columbia University
Abstract: When and how the motor cortex influences movement remains uncertain. The behavioral consequences of motor cortical inactivation suggest a circumscribed role. Yet across a broad array of behaviors including those that survive inactivation, motor cortical activity is correlated with muscle activation and motor cortical stimulation activates muscles. We addressed this ambiguity using measurement and perturbation of motor cortical activity together with electromyography in mice during two forelimb movements that differ in their requirement for motor cortical involvement. Rapid optogenetic silencing and electrical stimulation identified a short-latency pathway from motor cortex to spinal motor neurons activated only during one behavior. Analysis of motor cortical activity revealed a dramatic difference between behaviors in the coordination of firing patterns across neurons that can account for this differential pathway engagement. These results indicate a variation in the functional impact of motor cortex on downstream circuits that could enable behavior-specific control, helping to reconcile previous observations.