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a Brain Science Research Center, Tamagawa University Brain Science Institute, Machida, Tokyo, Japan b Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, Fuchu, Tokyo, Japan
Key Words: behavioral significance • caudate nucleus • decision making • goal-directed behavior • punishment • reward
Address for correspondence: Masamichi Sakagami, Brain Science Research Center, Tamagawa University Brain Science Institute, Tamagawa-gakuen, 6-1-1, Machida, Tokyo 194-8610, Japan. Voice: +81-42-739-8679; fax: +81-42-739-8663. sakagami{at}lab.tamagawa.ac.jp
The prefrontal cortex (PFC), particularly the lateral prefrontal cortex (LPFC), has an important role in cognitive information processing. The area receives projections from sensory association cortices and sends outputs to motor-related areas. Neurons in LPFC code the behavioral significance of stimuli, which can be abstract precursors for complex motor commands and are structured hierarchically. Loss of these neurons leads to a lack of flexibility in decision making, such as seen in stereotyped behaviors. However, to make more appropriate decisions the code for behavioral significance has to reflect the subject's own desires and demands. Indeed, LPFC has connections with reward-related areas, such as the orbitofrontal cortex (OFC), basal ganglia, and medial prefrontal cortex. Recently, many studies have reported reward modulation of neural codes of behavioral significance. Using an asymmetric reward paradigm, we can investigate the functional specificity of LPFC neurons that code both cognitive information and motivational information. In this review, we will discuss details of neuronal properties of LPFC neurons from the viewpoints of cognitive information processing and motivational information processing, and the question of how these two pieces of information are integrated. Abstract coding and contextual representations in the cognitive information processing are functional characteristics of LPFC. Such functional specificity in LPFC cognitive processes is supported by a long-term scale of reward history in the motivational information processing. The integration enables us to make an elaborate decision with respect to goal-directed behavior in complex circumstances.
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