2013年2月13日水曜日

Segregated Encoding of Reward–Identity and Stimulus–Reward Associations in Human Orbitofrontal Cortex


The Journal of Neuroscience, 13 February 2013, 33(7):3202-3211;
Miriam Cornelia Klein-Flügge, Helen Catharine Barron, Kay Henning Brodersen, Raymond J. Dolan, and Timothy Edward John Behrens

fMRI adaptation(同じ種類の刺激が続けて呈示されると、fMRI信号が低下する)を用いて、「刺激と報酬の連合」と「報酬の種類」、それぞれを保持している脳部位を分離。前者は外側眼窩前頭前野、後者は内側眼窩前頭前野に保持されている。

A dominant focus in studies of learning and decision-making is the neural coding of scalar reward value. This emphasis ignores the fact that choices are strongly shaped by a rich representation of potential rewards. Here, using fMRI adaptation, we demonstrate that responses in the human orbitofrontal cortex (OFC) encode a representation of the specific type of food reward predicted by a visual cue. By controlling for value across rewards and by linking each reward with two distinct stimuli, we could test for representations of reward–identity that were independent of associative information. Our results show reward–identity representations in a medial-caudal region of OFC, independent of the associated predictive stimulus. This contrasts with a more rostro-lateral OFC region encoding reward–identity representations tied to the predicate stimulus. This demonstration of adaptation in OFC to reward specific representations opens an avenue for investigation of more complex decision mechanisms that are not immediately accessible in standard analyses, which focus on correlates of average activity.

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