Social reward motivation increases working memory capacity

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To investigate the dynamic relationships between the visual working memory (VWM) and reward systems, we focused on the electroencephalograph (EEG) rhythms during a monetary incentive delayed-response task. 14 subjects were required to maintain several colored disks (3 or 6) during the retention interval. In case of the correct answer, they got the monetary reward which value (0, 10 or 50 Japanese yen) was presented at the beginning of each trial. Behavioral results showed that the VWM capacity for the high-reward condition was significantly increased as compared with the low- or no-reward conditions. EEG results showed that the frontal theta (6Hz) and the parietal alpha (12Hz) amplitudes are involved in the maintenance of the VWM since the activities increased during the retention interval and were correlated with the VWM capacity. The frontal beta delay-period amplitudes (24Hz) were significantly correlated with the increases of the VWM capacity from the high-reward to no-reward conditions. Interestingly, the frontal beta activity for reward motivation and the parietal alpha activity for VWM storage were significantly correlated under only the high-reward conditions. These findings suggest that the frontal-parietal system dynamically linked in beta and alpha frequency domains may implicate the increasing VWM capacity under high reward condition.