Delay activity of orbital and lateral prefrontal neurons of the monkey varying with different rewards.

We examined neuronal activity in the orbitofrontal cortex (OFC) in relation to reward expectancy and compared findings with those of the lateral prefrontal cortex (LPFC) in the monkey. Activity of OFC neurons was examined in a delayed reaction time task where every four trials constituted one block within which three kinds of rewards and no reward were delivered in a fixed order. More than half of OFC delay neurons were related to the expectancy of delivery or nodelivery of a reward as the response outcome, while some neurons showed nature-of-reward-specific anticipatory activity changes. These delay-related activities reflected the preference of the animal for each kind of reward and were modulated by the motivational state of the animal. LPFC neurons are reported to show nature-ofreward-specific anticipatory activity changes in a delayed response task when several different kinds of rewards are used. Such rewarddependent activity is observed in LPFC delay neurons both with and without spatially differential delay (working memory-related) activity. Although reward expectancy-related activity is commonly observed in both OFC and LPFC, it is suggested that the OFC is more concerned with motivational aspects, while the LPFC is related to both the cognitive and motivational aspects of the expectancy of response outcome.