Motor cortex can directly drive the globus pallidal neurons in a projection neuron type dependent manner in rat

The basal ganglia (BG) are critical for the control of motor behaviors and for reinforcement learning. Here, we demonstrate in rats that primary and secondary motor areas (M1 and M2) make functional synaptic connections in the globus pallidus (GP), not usually thought of as an input site of the BG using optogenetics and morphological analysis. The cortical excitation in the GP was as strong as that in the STN. GP neurons projecting to the striatum were preferentially innervated by the motor cortex. Morphological observation revealed that the density of axonal boutons from motor cortices in the GP was approximately 30% of that in the striatum, but was comparable to that in the STN. M1 and M2 projected differentially to the BG in terms of topography and substructures. These results suggest that cortico-pallidal innervation is an additional excitatory input to the BG, and can affects behaviors via the cortex-basal ganglia-thalamus loop.