Convergence of inputs from the basal ganglia with layer 5 of motor cortex and cerebellum in mouse motor thalamus.

In this study, we extend the common conception of the basal ganglia as an information loop: flowing from cortex to basal ganglia, to thalamus, and back to cortex. We used tricolor viral labeling and an optogenetic approach to reveal that projections from the output nuclei of the basal ganglia converge with inputs from both layer 5 of primary motor cortex and the deep cerebellar nuclei onto individual thalamic relay cells. Not only do these findings add nuance to the notion that cerebellar and basal ganglia circuits through motor thalamus are independent, but also highlight a novel intersection between basal ganglia and cortex that countervails long-held conceptions of how the brain handles motor commands.