Most natural actions are chosen voluntarily from many possible choices. An action is often chosen based on the reward that it is expected to produce. What kind of cellular activity in which area of the cerebral cortex is involved in selecting an action according to the expected reward value? Results of an analysis in monkeys of cellular activity during the performance of reward-based motor selection and the effects of chemical inactivation are presented. We suggest that cells in the rostral

more »

... ulate motor area, one of the higher order motor areas in the cortex, play a part in processing the reward information for motor selection. The cingulate motor areas (CMAs) of primates reside in the banks of the cingulate sulcus in the medial surface of the cerebral hemisphere and are subdivided into rostral and caudal parts (1). Anatomical studies have revealed prominent afferent input to the CMAs from the limbic structures and the prefrontal cortex, which can send information about motivation and the internal state of subjects, as well as cognitive evaluation of the environment (2, 3). The CMAs send output to the primary and secondary motor areas and other motor structures in the brainstem and spinal cord (4). The CMAs are thought to be in a pivotal position to process the information necessary to select voluntary actions in accordance with the subject's internal and external requirements because of this anatomical connectivity (5-7). However, it is not yet known exactly how the CMAs are used or how individual cells behave in relation to the actual performance of motor tasks requiring motor selection based on reward evaluation. Therefore, we devised an experimental model of reward-based motor selection and analyzed cellular activity in the CMAs. We trained three monkeys (Macaca fuscata) to perform two different arm movements, either pushing or turning a handle, in response to a visual trigger signal (8, 9). The essence of the motor task was that the animals voluntarily selected one of the two movements based on the amount of reward.