Abstract
In rodents, the medial prefrontal cortex (PFC) is involved in the suppression of temporally inappropriate responses. This raises a possibility that the PFC plays an important role in a delayed reinforcement operant task. If so, the PFC may exhibit neuronal activities during the delay period related to withholding the impulse to respond or timing the response correctly. To address this issue, we investigated the effects of transient PFC inactivation on a delayed reinforcement lever-press task. The effects of hippocampal inactivation were also tested for comparison. In a separate experiment, we recorded the multiple unit activities (MUAs) of the PFC during the task. The inactivation experiment showed the involvement of the prefrontal cortex in this task: prefrontal cortex inactivation but not hippocampal inactivation significantly impaired the performance of the delayed reinforcement task. The present MUA analysis revealed a significant decrease in the PFC neuronal activities during the delay period. These results indicate the involvement of the rat PFC at least in a certain type of delayed reinforcement operant behavior, in which a sustained decrease in the PFC neuronal activities during the delay period may play a role in a neuronal function performed by the PFC in the inhibitory control of behavior. [J Physiol Sci. 2008;58 Suppl:S143]
