Abstract
Current computational accounts posit that, in simple binary choices, humans accumulate evidence in favour of the different alternatives before committing to a decision. Neural correlates of this accumulating activity have been found during perceptual decisions in parietal and prefrontal cortex; however the source of such activity in value-based choices remains unknown. Here we use simultaneous EEG–fMRI and computational modelling to identify EEG signals reflecting an accumulation process and demonstrate that the within- and across-trial variability in these signals explains fMRI responses in posterior-medial frontal cortex. Consistent with its role in integrating the evidence prior to reaching a decision, this region also exhibits task-dependent coupling with the ventromedial prefrontal cortex and the striatum, brain areas known to encode the subjective value of the decision alternatives. These results further endorse the proposition of an evidence accumulation process during value-based decisions in humans and implicate the posterior-medial frontal cortex in this process.
Highlights
Current computational accounts posit that, in simple binary choices, humans accumulate evidence in favour of the different alternatives before committing to a decision
Evidence supporting this mechanism comes from recent electroencephalography (EEG) studies in humans, which report that electrical activity measured on the scalp builds up gradually over time during perceptual decisions[5,6,7,8,9], and from functional magnetic resonance imaging studies, which propose that this activity is generated in sensorimotor and higherlevel prefrontal areas[10,11,12,13,14,15]
We combined computational modelling and simultaneous recordings of EEG and functional magnetic resonance imaging (fMRI) to identify a cortical area in posterior-medial frontal cortex (pMFC) reflecting evidence accumulation (EA) during value-based decisions
Summary
Current computational accounts posit that, in simple binary choices, humans accumulate evidence in favour of the different alternatives before committing to a decision. Consistent with its role in integrating the evidence prior to reaching a decision, this region exhibits task-dependent coupling with the ventromedial prefrontal cortex and the striatum, brain areas known to encode the subjective value of the decision alternatives These results further endorse the proposition of an evidence accumulation process during value-based decisions in humans and implicate the posterior-medial frontal cortex in this process. We hypothesize that if the relevant accumulator regions in the brain exist, an electrophysiologically derived measure of the process of EA should covary on a trial-by-trial basis with activity in these regions To test this hypothesis, we coupled high temporal resolution, single-trial, EEG with simultaneously acquired fMRI23,24 and computational modelling to (1) uncover the process of EA in the broadband EEG signal and (2) confirm its presence by localizing its source with fMRI during a value-based decision-making task. We provided evidence that the pMFC exhibits task-dependent coupling with the ventromedial prefrontal cortex (vmPFC) and the striatum, further implicating this region in accumulating information for value-based decisions
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