Motivation-dependent communication between cortex and brainstem

Neurons in the medullary brainstem exhibit movement-related patterns of activity, but the neuronal population codes that specify distinct actions, and the mechanisms by which cortex may shape these codes as a function of motivational state, remain unclear. To explore whether coupling between cortex and medulla depends upon motivational context, we trained mice to make both pre-reward "appetitive" licks that served to trigger water availability and rapidly attenuated with satiety, and "consummatory" licks, which occur post-reward release and more slowly attenuated with satiety. Simultaneous recordings from secondary motor cortex and motor medulla revealed that medullary activity was more time-locked than cortical activity to individual licks and exhibited a phase-based population code that encoded lick direction. Correlations between cortex and medulla were stronger during appetitive licks than during consummatory licks, with causal dependency established by optogenetic intervention and supported by multi-region recurrent network models. Population codes underlying behavior shared across the central nervous system, exemplified by cortico-medullary coupling, thus may depend upon the motivational context underlying action.