To investigate neuronal mechanisms of higher cognitive activity, single neuronal activity has been recorded from the prefrontal cortex of monkeys trained in cognitive tasks. It has been well documented that there are prefrontal neurons which are involved in cognitive operations such as coding the meaning of a stimulus or retaining information in working memory. On the other hand, there are also prefrontal neurons which show reward-related activity changes. Two kinds of reward-related activities are found in the primate prefrontal cortex; one kind is concerned with processing post-trial events such as coding the reinforcement and/or error, and the other is concerned with the expectancy of the specific reward. These reward-related activities, which appear to be involved in motivational operations, are related also to cognitive operations such as coding the context in which the reward is given or omitted, or monitoring the context concerning the task situation with which the animal is faced. It seems that the prefrontal cortex is involved in the integration of cognitive and motivational information for goal-directed behavior. While the function of the prefrontal cortex is often associated with working memory, I introduce the idea that the prefrontal cortex plays important roles for coding, monitoring and providing the context for goal-directed behavior.