2013年11月13日水曜日

Single-Neuron Mechanisms Underlying Cost-Benefit Analysis in Frontal Cortex

Takayuki Hosokawa, Steven W. Kennerley, Jennifer Sloan, and Jonathan D. Wallis
J. Neurosci. 2013;33 17385-17397

サルが報酬を得るために「努力が必要な課題」、「単に一定時間待てばよい課題」を行う。
前頭前野(OFC、DLPFC)の多くのニューロンが、「どちらの課題をやっているのか」という情報をコードしていた。
→ これらの部位は「意思決定における価値」ではなく「状況のカテゴリー分け」に関わっているのでは?

Effective decision-making requires consideration of costs and benefits. Previous studies have implicated orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) in cost-benefit decision-making. Yet controversy remains about whether different decision costs are encoded by different brain areas, and whether single neurons integrate costs and benefits to derive a subjective value estimate for each choice alternative. To address these issues, we trained four subjects to perform delay- and effort-based cost-benefit decisions and recorded neuronal activity in OFC, ACC, DLPFC, and the cingulate motor area (CMA). Although some neurons, mainly in ACC, did exhibit integrated value signals as if performing cost-benefit computations, they were relatively few in number. Instead, the majority of neurons in all areas encoded the decision type; that is whether the subject was required to perform a delay- or effort-based decision. OFC and DLPFC neurons tended to show the largest changes in firing rate for delay- but not effort-based decisions; whereas, the reverse was true for CMA neurons. Only ACC contained neurons modulated by both effort- and delay-based decisions. These findings challenge the idea that OFC calculates an abstract value signal to guide decision-making. Instead, our results suggest that an important function of single PFC neurons is to categorize sensory stimuli based on the consequences predicted by those stimuli.

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