2014年4月1日火曜日

A neural mechanism underlying failure of optimal choice with multiple alternatives

Bolton K H Chau, Nils Kolling, Laurence T Hunt, Mark E Walton & Matthew F S Rushworth
Nature Neuroscience (2014) doi:10.1038/nn.3649

二つの選択肢間の意思決定において,三番目の選択肢が現れたらどうなるのか?
「三番目の選択肢の価値が低い」時の方が,元々の選択が正確にできなくなる.
また,その際には,「二つの選択肢の価値の差」をコードしている前頭前野内腹側部(vmPFC)の活動が低下している.

Despite widespread interest in neural mechanisms of decision-making, most investigations focus on decisions between just two options. Here we adapt a biophysically plausible model of decision-making to predict how a key decision variable, the value difference signal—encoding how much better one choice is than another—changes with the value of a third, but unavailable, alternative. The model predicts a surprising failure of optimal decision-making: greater difficulty choosing between two options in the presence of a third very poor, as opposed to very good, alternative. Both investigation of human decision-making and functional magnetic resonance imaging–based measurements of value difference signals in ventromedial prefrontal cortex (vmPFC) bore out this prediction. The vmPFC signal decreased in the presence of low-value third alternatives, and vmPFC effect sizes predicted individual variation in suboptimal decision-making in the presence of multiple alternatives. The effect contrasts with that of divisive normalization in parietal cortex.

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