Inferior parietal lobule supports decision making under uncertainty in humans

The optimal responses for many decisions faced by humans are ill defined, yet we are able to choose well by associating choices with outcomes, and employing this information in decision making. Previous studies suggest that the parietal cortex is involved in "uncertain" decision making, yet uncertainty is confounded with increased difficulty and attention. Here we aim to dissociate the role of parietal cortex in decision making and attention. Using functional magnetic resonance imaging we measured brain activity while participants played a "matching-pennies" game. We found that the inferior parietal lobule is involved in decision making under uncertainty, showing higher activity when the decision was uncertain rather than certain and when humans were given trial-by-trial feedback on choice outcomes than when they were not. Crucially, increasing attentional load with secondary tasks reduced inferior parietal activity when decisions were made under uncertainty, suggesting that general attention does not drive its activation. This pattern was consistent for visual or auditory feedback, and for direct (symbols representing wins and losses) or indirect (only the opponent's choices were shown) feedback. It contrasted with results from medial superior frontal gyrus, which was driven primarily by increased attentional load. We suggest that decision making under uncertainty is dissociable from general attention in the brain.