Neuronal activity representing temporal prediction of reward in the primate prefrontal cortex.
Temporal prediction of future events, especially regarding reward delivery, is critical for controlling/learning purposeful behavior. The dorsolateral prefrontal cortex (DLPFC) has been considered to be involved in behavioral control based on prospective coding for future events, including reward. Thus this area is likely to have a neuronal mechanism responsible for temporal prediction of forthcoming reward. To address this hypothesis, we recorded the neuronal activity from the DLPFC of macaque monkeys while they performed an oculomotor delayed-response task under two conditions regarding the time of reward delivery. In this task, when the subjects made a correct response, the reward was delivered after a reward-delay period of 0.5 or 2 s. At the behavioral level, the onset latency for saccades was significantly faster in the shorter reward-delay trials (0.5 s) than in longer reward-delay trials (2 s), indicating that our subjects actually predicted the time of reward delivery. At the neuronal level, we found that many DLPFC neurons showed differential activity depending on the predicted time of reward delivery during the cue and/or delay periods. These results suggest that a fraction of neurons in the DLPFC represent the temporal prediction of reward and probably a variety of other future events.