Motor cortical output for skilled forelimb movement is distributed across projection neuron classes

Datasets and code associated with the above named study. Manuscript abstract: The interaction of descending neocortical outputs and subcortical premotor circuits is critical for shaping the skilled execution of limb movements. Two broad classes of motor cortical output projection neurons provide input to many subcortical motor areas: pyramidal tract neurons (PT), which project throughout the neuraxis; and intratelencephalic neurons (IT), which project within cortex and to subcortical striatum. It is unclear whether these classes are functionally in series or whether separable components of descending motor control signals are distributed across these distinct classes of projection neurons. Here we combine large-scale neural recordings across all layers of motor cortex with cell-type specific perturbations to study cortically-dependent mouse motor behaviors: kinematically-variable manipulation of a joystick and a kinematically-precise reach-to-grasp. We find that striatum-projecting IT neuron activity preferentially codes for speed and amplitude of forelimb movements whereas pons-projecting PT neurons preferentially code for movement direction. Consistent with these distinct neural correlates, optogenetic silencing of IT projection neurons produced large decreases in the speed and extent of movement in both tasks whereas inactivation of corticopontine PT neurons modified movement direction. These data suggest that separable components of descending motor cortical commands are distributed across corticostriatal IT and corticopontine PT pathways to shape skilled, flexible movements.