Data from: A neural mechanism underlying failure of optimal choice with multiple alternatives

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.behav_fmri Behavioral data of the main experiment (matlab data) behav_pilot1 Behavioral data of Pilot Study 1 reported in SI.6 (matlab data) behav_pilot2 Behavioral data of Pilot Study 2 reported in SI.6 (matlab data) behav_pilot3 Behavioral data of Pilot Study 3 reported in SI.6 (matlab data) behav_3options Behavioral data of the three-option experiment reported in SI.7 and 8 (matlab data) behav_hk Unpublished data of a new experiment. The experiment involved the identical task paradigm that is published in Chau et al., Nature Neursocience, 2014, except: 1. It contained only distractor trials. 2. It contained new trials where all options were associated with negative reward magnitudes (i.e. losses). behav_hk.mat (Updated in Feb 2020