Role for cells in the cingulate motor area of the monkey

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The purpose of the present study was to examine how neuronal activity in the rostral cingulate motor area (CMAr) is involved in the movenent alteration based on the evaluation of reward. Two monkeys (Macaca fuscata) were trained to perform two different arm movements (turn or pull a handle), in response to visual trigger signal (LED). Each movement was started from a neutral position. Initially, the monkey has to guess which of two movements was correct. The correct movement was rewarded with a drop of fruit juice (0.1ml). The correct movememt was not changed during in a block of trials (5-11 trials of constant-reward), requiring the monkeys to keep selecting the same movement. Thereafter, the amount of reward was progressively decreased by 30% per trial, if the monkey repeated the same movement. At this stage of the behavioral time schedule, the monkeys were free to select a alternative movement. If they did movement alteration, the alternative movement was now defined as a correct movement. The amount of reword came back to its full amount, and a new series of the constant-reward trials begun. In CMAr, about 28% of task-related neurons were active during a interval between the occurrence of reduced reward and the initiation of a selected movement that was different from a previously performed movement. Remaining neurons were active in relation to movement initiation or during a period of preparation for a next movement. In contrast, cells in the caudal cingulate motor area (CMAc) and in the primary motor cortex (MI) were mostly related to the execution of movement or motor preparation. Only small number of CMAc cells (3%) and MI cells (1%) exhibited activity related to motor selection. These observations indicate that the CMAr plays a role in motor alteration or motor selection based on the reward evaluation. On the other hand, neither the CMAc and the MI are the cortical sites where the reward information is processed for the purpose of motor selection.