Primate Ventromedial Prefrontal Cortex Neurons Continuously Encode the Willingness to Engage in Reward-Directed Behavior.

To survive in their complex environment, primates must integrate information over time and adjust their actions beyond immediate events. The underlying neurobiological processes, however, remain unclear. Here, we assessed the contribution of the ventromedial prefrontal cortex (VMPFC), a brain region important for value-based decision-making. We recorded single VMPFC neurons in monkeys performing a task where obtaining fluid rewards required squeezing a grip. The willingness to perform the action was modulated not only by visual information about Effort and Reward levels but also by contextual factors such as Trial Number (i.e., fatigue and/or satiety) or behavior in recent trials. A greater fraction of VMPFC neurons encoded contextual information, compared with visual stimuli. Moreover, the dynamics of VMPFC firing was more closely related to slow changes in motivational states driven by these contextual factors rather than rapid responses to individual task events. Thus, the firing of VMPFC neurons continuously integrated contextual information and reliably predicted the monkeys's willingness to perform the task. This function might be critical when animals forage in a complex environment and need to integrate information over time. Its relation with motivational states also resonates with the VMPFC's implication in the "default mode" or in mood disorders.