Abstract
Motor cortex is part of a network of central brain circuits that together enable robust, flexible, and efficient movement in mammals. Recent work has revealed rich dynamics in mammalian motor cortex 1–7 thought to underlie robust and flexible movements. These dynamics are a consequence of recurrent connectivity between individual cortical neuron subtypes8, but it remains unclear how such complex dynamics relate to individual cell types and how they covary with continuous behavioral features. We investigated this in mice, combining a self-paced, kinematically-variable, cortex-dependent, bimanual motor task 9,10 with large-scale neural recordings that included cell-type information. This revealed highly distributed correlates of movement execution across all layers of forelimb motor cortex and subcortical areas. However, we observed a surprising relative lack of modulation in the putative source of motor commands brain-stem projecting (pyramidal tract, PT) neurons 11. By contrast, striatal/cortical projecting (intratelencephalic, IT) neurons showed much stronger correlations with movement kinematics. Cell-type specific inactivation of PT neurons during movement execution had little effect on behavior whereas inactivation of IT neurons produced dramatic decreases in the speed and amplitude of forelimb movements. PT inactivation elicited rapid, compensatory changes in activity distributed across multiple cortical layers and subcortical regions helping to explain minimal effects of inactivation on behavior. This work illustrates how cortical-striatal population dynamics play a critical role in the control of movement while maintaining substantial flexibility in the extent to which PT projection neurons are a requisite contributor to descending motor commands.
