The spatio-temporal pattern of reward processing : magnetoencephalographic responses to value appraisal and reward prediction in a gambling task

Abstract

Reward processing is frequently examined in decision-making designs, as they involve essential components like evaluation of value and reward prediction. The present study examined magnetoencephalographic (MEG) correlates of such components in 20 volunteers: subjects had to decide, whether or not to gamble for 10 or 50 c (Eurocent), which they could win with 10%, 50% or 90% chance. MEG responses to the visually presented value (10 or 50 c) and chance (10, 50 or 90%) stimuli, analyzed using Minimum Norm Estimates (MNE), distinguished value evaluation and reward prediction in time windows between 150 and 350 ms after stimulus onset in different brain areas: righthemispheric temporo-parietal dipole activity 150 230 ms distinguished value evaluation (po .01), whereas the chance prediction varied with right-hemispheric temporo-parietal dipole activity at 215 255 ms (p o .05), bilateral fronto-temporal dipole activity at 235 275 ms (p o .01) and frontal dipole activity at 250 350 ms (p o .05). Frontal activity was larger and decision time was longer on risky trials (decision to gamble at 50% chance). Activation of the same region by both cues (value and chance) suggests that reward processing comprises the interaction of preferred value and expectancy of outcome, while the course of activity suggests a consecutively activated neuronal network of reward processing, including posterior temporal to prefrontal regions.