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報酬 2
Reward 2

開催日 2014/9/12
時間 16:00 - 17:00
会場 Room H(304)
Chairperson(s) 坂上 雅道 / Masamichi Sakagami (玉川大学脳科学研究所 / Tamagawa University, Brain Science Institute, Japan)
設楽 宗孝 / Munetaka Shidara (筑波大学医学医療系 / University of Tsukuba, Faculty of Medicine, Japan)

The cost paid for the reward enhances the value of the reward

  • O2-H-4-4
  • 田中 慎吾 / Shingo Tanaka:1 O'Doherty John P / John P O'Doherty:2 坂上 雅道 / Masamichi Sakagami:1 
  • 1:玉川大学 / Brain Science Institute, Tamagawa University, Japan 2:カリフォルニア工科大学、アメリカ / Caltech, CA, USA 

"One of the greatest joys in life is an ice cold beer after a hard day of work." As this phrase indicates, the value of a reward can be modulated by the effort or the cost put into its achievement. However, relatively few studies have shown the neural basis of the effect caused by the paid cost on the value of the reward. When calculating the values of rewards in the basal ganglia, the activity of dopamine neurons, which represent the reward prediction error, is used to update the value. Although recent reports indicate the cost information is transmitted to dopamine neurons, it is still unclear whether the paid cost modulates the activity of dopamine neurons. Here, we examined whether the activity of the dopamine neurons in response to the reward predictive cues was increased by the cost preceding to these cues.
Two macaque monkeys performed a saccade task. After fixation on a fixation point, the subjects were required to make a saccade to a condition cue and then a target appeared. In the high cost condition, long fixation to the target was required. In the low-cost condition, only a short fixation was required. After fixation on the target, the subjects made a saccade to the reward cue and obtained the reward.
While the subjects performed the saccade task, the activities of dopamine neurons were recorded from the SNc in the midbrain. The dopamine neurons showed phasic responses to the condition cues and the reward cues. The neuronal response to the low-cost cue was larger than that to the high-cost cue. This difference in the activity of the dopamine neurons was independent of the subtype of dopamine neurons. In contrast, the responses to the reward cue after the high-cost condition were larger than those to the reward cue after the low-cost condition indicating that the paid cost increases the reward prediction error signal. We also showed that the paid cost enhances the learning speed in an exploration task, in which the subjects have to learn the relationship between the reward cue and the reward trial-by-trial. Furthermore, the paid cost increased the response of the dopamine neurons to the reward itself. From these results, we suggest that information about the cost is integrated in the dopamine neurons and the paid cost amplifies the value of the reward.

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