Activity of primate orbitofrontal and dorsolateral prefrontal neurons: task-related activity during an oculomotor delayed-response task.

The orbitofrontal cortex (OFC) has strong reciprocal connections to the dorsolateral prefrontal cortex (DLPFC), which is known to participate in spatial working memory processes. However, it is not known whether or not the OFC also participates in spatial working memory and whether the OFC and DLPFC contribute equally to this process. To address these issues, we collected single-neuron activity from both areas while a monkey performed an oculomotor delayed-response task, and compared the characteristics of task-related activities between the OFC and DLPFC. All of the task-related activities observed in the DLPFC were also observed in the OFC. However, the proportion and response characteristics of task-related activities were different between the two areas. While most delay-period activity observed in the DLPFC was directionally selective and showed tonic sustained activation, most delay-period activity observed in the OFC was omni-directional and showed gradually increasing activity. Reward-period activity was predominant among task-related activities in the OFC. The proportion of neurons showing reward-period activity was significantly higher in the OFC than in the DLPFC. These results suggest that, although both the OFC and DLPFC participate in spatial working memory processes, the OFC is related more to the expectation and the detection of reward delivery, while the DLPFC is related more to the temporary maintenance of spatial information and its processing.