The source of Intellectual activity-Neural basis of Default activity

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Two monkeys were trained in a WM (spatial delayed alternation) task. We examined dopamine release while the monkey was (1) performing the WM task with a liquid reward (WM task period) and (2) sitting quietly without task performance and without reward (REST period). During the WM task period, we observed a significant decrease in dopamine release compared with during the REST period in the medial prefrontal cortex (PFC). Neuroimaging studies have indicated activations of the dorsolateral PFC in relation to WM task performance, and increased dopamine release in the dorsolateral PFC is considered to play essential roles in WM task performance. In contrast, in the medial PFC, we observed increases in both the rCBF and dopamine release during REST as compared with WM task period. Our results suggest that cognitive operations associated with default-mode brain activity in the medial PFC may be supported by the increased dopamine release.