2014年5月29日木曜日

Distributed Value Representation in the Medial Prefrontal Cortex during Intertemporal Choices

Qiang Wang, Shan Luo, John Monterosso, Jintao Zhang, Xiaoyi Fang, Qi Dong, and Gui Xue
The Journal of Neuroscience, 28 May 2014, 34(22):7522-7530;

異時点間の意思決定。
「すぐにもらえる(少量の)報酬」と「後でもらえる(多量の)報酬」のどちらを選ぶか?
前者の価値は背内側前頭前野(dmPFC)の後部で、後者の価値は前部で処理されている。
また、「二つの選択肢の価値の差」は腹内側前頭前野(vmPFC)でコードされている。

The ability to resist current temptations in favor of long-term benefits is a critical human capacity. Despite the extensive studies on the neural mechanisms of intertemporal choices, how the subjective value of immediate and delayed rewards is represented and compared in the brain remains to be elucidated. The present fMRI study addressed this question by simultaneously and independently manipulating the magnitude of immediate and delayed rewards in an intertemporal decision task, combined with univariate analysis and multiple voxel pattern analysis. We found that activities in the posterior portion of the dorsal medial prefrontal cortex (DmPFC) were modulated by the value of immediate options, whereas activities in the adjacent anterior DmPFC were modulated by the subjective value of delayed options. Brain signal change in the ventral mPFC was positively correlated with the “relative value” (the absolute difference of subjective value between two intertemporal alternatives). In contrast, the dorsal anterior cingulate cortex activity was negatively correlated with the relative value. These results suggest that immediate and delayed rewards are separately represented in the dorsal mPFC and compared in the ventral mPFC to guide decisions. The functional dissociation of posterior and anterior DmPFC in representing immediate and delayed reward is consistent with the general structural and functional architecture of the prefrontal cortex and may provide a neural basis for human's unique capacity to delayed gratification.

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