Motivation-dependent communication between cortex and brainstem

Recent studies have revealed that neurons in the medullary brainstem display patterns of activity linked to movement, but the specific neuronal codes representing different actions, as well as how the cortex influences these codes based on motivation, are still not fully understood. To investigate the role of motivation in the communication between the cortex and medulla, researchers trained mice to perform two types of licks: appetitive licks, which were made before receiving water and decreased as satiety set in, and consummatory licks, which occurred after water release and took longer to diminish with satiety.

By simultaneously recording from secondary motor cortex and the motor medulla, scientists discovered that medullary activity was more time-locked to individual licks than cortical activity and exhibited a phase-based population code that encoded lick direction. The correlations between the cortex and medulla were found to be stronger during appetitive licks compared to consummatory licks.

This difference in coupling strength was established through causal intervention using optogenetics and further supported by multi-region recurrent network models.

This research demonstrates that population codes governing behavior are shared across the central nervous system, as evidenced by the coupling between the cortex and medulla. However, this coupling may vary depending on the motivational context underlying the action, suggesting that the central nervous system adapts its communication methods to facilitate appropriate responses based on the individual's motivation level.