Refinement of corticospinal neuron activity during skilled motor learning

The learning of motor skills relies on plasticity of the primary motor cortex as task acquisition drives the remodeling of cortical motor networks1,2. Large scale cortical remodeling of evoked motor outputs occurs in response to the learning of skilled, corticospinal-dependent behavior, but not simple, unskilled tasks1. Here we determine the response of corticospinal neurons to both skilled and unskilled motor training and assess the role of corticospinal neuron activity in the execution of the trained behaviors. Using in vivo calcium imaging, we found temporal coding of corticospinal activity coincided with the development of skilled, but not unskilled, motor expertise. Animals that failed to learn our skilled, precision isometric pull task exhibited a limited repertoire of dynamic movements and reduced network modulation. Transection of the corticospinal tract and optogenetic regulation of corticospinal activity show the necessity for patterned corticospinal network activity in the execution of skilled, but not unskilled, movement. We reveal a critical role for corticospinal network modulation in the learning and execution of skilled motor movements. The integrity of the corticospinal tract is essential to the recovery of dexterous movement after central nervous system injuries and these findings should help to shape translational approaches to motor recovery.