Abstract
Long-standing clinical observations in frontal-lesioned patients have suggested an active involvement of the prefrontal cortex in the organization and control of goal-directed actions. Only recently has this involvement started to be experimentally investigated in the field of neurophysiology, with an introduction of a new behavioral paradigm. That is, the free-choice task, in which subjects are required to choose their responses with regard to their possible outcomes. We have recently recorded prefrontal neuronal activity during the performance of two different types of the free-choice task. One is the variable probability task, in which subjects were required to choose either stimulus A or B in every trial, as the reward probability for each stimulus varied systematically over trials depending on the subjects’ choice. The other is the save/spend task, in which subjects were required to choose either stimulus A (‘save’ cue) or B (‘spend’ cue) in every trial, which delivers no reward but increases the amount of reward in the future, or delivers the accumulated reward, respectively. With both tasks, we found a number of prefrontal neurons firing differentially preceding the movement, depending on the purpose of the movement (choose A or B), as well as, or independent of, the direction of movement (go left or right). The experimenter could predict which stimulus the subject was going to choose by looking at the activity of these neurons. These neurons may play a critical role in many decision-making situations, in which the abstract planning of behavior should precede the concrete preparation of movements. [Jpn J Physiol 55 Suppl:S51 (2005)]
