2014年5月22日木曜日

Reward Inference by Primate Prefrontal and Striatal Neurons

Xiaochuan Pan, Hongwei Fan, Kosuke Sawa, Ichiro Tsuda, Minoru Tsukada, and Masamichi Sakagami
J. Neurosci. 2014;34 1380-1396 Open Access

サル電気生理。
線条体と前頭前野背側部はどちらも「報酬予測」に関連している。
直接経験に依る単純な報酬予測だけではなく、線条体は「消去法から導きだされる予測」、前頭前野外側部は「推移律から導きだされる予測」をそれぞれできる。
線条体って思ったより賢い!

The brain contains multiple yet distinct systems involved in reward prediction. To understand the nature of these processes, we recorded single-unit activity from the lateral prefrontal cortex (LPFC) and the striatum in monkeys performing a reward inference task using an asymmetric reward schedule. We found that neurons both in the LPFC and in the striatum predicted reward values for stimuli that had been previously well experienced with set reward quantities in the asymmetric reward task. Importantly, these LPFC neurons could predict the reward value of a stimulus using transitive inference even when the monkeys had not yet learned the stimulus–reward association directly; whereas these striatal neurons did not show such an ability. Nevertheless, because there were two set amounts of reward (large and small), the selected striatal neurons were able to exclusively infer the reward value (e.g., large) of one novel stimulus from a pair after directly experiencing the alternative stimulus with the other reward value (e.g., small). Our results suggest that although neurons that predict reward value for old stimuli in the LPFC could also do so for new stimuli via transitive inference, those in the striatum could only predict reward for new stimuli via exclusive inference. Moreover, the striatum showed more complex functions than was surmised previously for model-free learning.

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