[Motivational control of learning in the prefrontal cortex]

The prefrontal cortex (PFC), which is considered to be the center of executive control, also plays important roles in motivational operations. Neurons related to the expectancy of the presence or absence of a particular reward in a task situation are present in the primate lateral, medial and orbital PFC; these neurons show differential delay activity between reward and no-reward trials as well as showing differential delay activity between different types of reward trials. Reward expectancy-related neuronal activities reflect the motivation of animals to obtain the reward. Behavioral studies indicate that better learning is achieved when a more preferred reward is used. In primate lateral PFC neurons, cognitive task (e.g., working memory)-related activity is enhanced when a more preferred reward is used. Thus, motivation appears to modulate learning-related neuronal activity that in turn modulates learning-related behavior. Expectancies of outcome can also be advantageous during learning if animals exhibit different reactions for different outcomes, as different expectancies develop for different outcomes. Thus, differential outcome expectancies may facilitate learning and discriminative performance by providing the subject with an additional source of information. Motivation is induced not only by homeostatic (such as food and liquid) but also by nonhomeostatic rewards (such as seeing and manipulating interesting objects). The expectancy of both types of rewards could modulate learning at both the neuronal and behavioral levels.