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

The interaction of descending neocortical outputs and subcortical premotor circuits is critical for shaping the skilled 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 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 represents amplitude whereas pons-projecting PT neurons preferentially represent the variable direction of forelimb movements. Thus, separable components of descending motor cortical commands are distributed across motor cortical projection cell classes. One-sentence summarySeparable components of cortical motor commands are distributed across distinct glutamatergic projection neuron cell-types.