Dynamic changes in representations of preceding and upcoming reward in monkey orbitofrontal cortex.

We investigated how orbitofrontal cortex (OFC) contributes to adaptability in the face of changing reward contingencies by examining how reward representations in monkey orbitofrontal neurons change during a visually cued, multi-trial reward schedule task. A large proportion of orbitofrontal neurons were sensitive to events in this task (69/80 neurons in the valid and 48/58 neurons in the random cue context). Neuronal activity depended upon preceding reward, upcoming reward, reward delivery, and schedule state. Preceding reward-dependent activity occurred in both the valid and random cue contexts, whereas upcoming reward-dependent activity was observed only in the valid context. A greater proportion of neurons encoded preceding reward in the random than the valid cue context. The proportion of neurons with preceding reward-dependent activity declined as each trial progressed, whereas the proportion encoding upcoming reward increased. Reward information was represented by ensembles of neurons, the composition of which changed with task context and time. Overall, neuronal activity in OFC adapted to reflect the importance of different types of reward information in different contexts and time periods. This contextual and temporal adaptability is one hallmark of neurons participating in executive functions.