Alpha suppression over parietal electrode sites predicts decisions to trust

Decisions to trust help form the basis of relationships and society yet little is known about their neurophysiology. We told participants they were playing a coin toss game with a trustworthy and an untrustworthy person and measured their neural activity with EEG as they decided whether to trust those fictitious interaction partners. Target people ostensibly correctly reported the outcome of a coin toss on 66% of trials. Behaviorally, participants probability matched and chose to trust the reported coin flips from each profile equally by the end of 100 trials. Electrophysiologically, there were reliable differences in the pattern of oscillatory activity in the alpha band (8-13Hz) over parietal electrode sites 1-3 s prior to their trust decisions. Specifically, for trustworthy profiles, there was greater alpha suppression for trust decisions vs. distrust decisions. Conversely, for untrustworthy profiles there was greater alpha suppression for distrust decisions vs. trust decisions. This differential activity (trust minus distrust) also predicted the number of trust decisions made. Our results indicate that the intentions to trust people form very early in the processing stream and manifest as alpha suppression over parietal cortex.