Choosing between small, likely rewards and large, unlikely rewards activates inferior and orbital prefrontal cortex

Abstract

Patients sustaining lesions of the orbital prefrontal cortex (PFC) exhibit marked impairments in the performance of laboratory-based gambling, or risk-taking, tasks, suggesting that this part of the human PFC contributes to decision-making cognition. However, to date, little is known about the particular regions of the orbital cortex that participate in this function. In the present study, eight healthy volunteers were scanned, using H(2)(15)0 PET technology, while performing a novel computerized risk-taking task. The task involved predicting which of two mutually exclusive outcomes would occur, but critically, the larger reward (and penalty) was associated with choice of the least likely outcome, whereas the smallest reward (and penalty) was associated with choice of the most likely outcome. Resolving these "conflicting" decisions was associated with three distinct foci of regional cerebral blood flow increase within the right inferior and orbital PFC: laterally, in the anterior part of the middle frontal gyrus [Brodmann area 10 (BA 10)], medially, in the orbital gyrus (BA 11), and posteriorly, in the anterior portion of the inferior frontal gyrus (BA 47). By contrast, increases in the degree of conflict inherent in these decisions was associated with only limited changes in activity within orbital PFC and the anterior cingulate cortex. These results suggest that decision making recruits neural activity from multiple regions of the inferior PFC that receive information from a diverse set of cortical and limbic inputs, and that the contribution of the orbitofrontal regions may involve processing changes in reward-related information.

Figures

Fig. 1.

Typical displays from the decision-making task, and associated behavioral data across the present study.A, C,E, Example decision from the 4:2 condition, percentage of choice of the most likely outcome and mean deliberation times as a function of the balance of reward associated with the two outcomes. B, D,F, Example decision from the 5:1 condition, percentage of choice of the most likely outcome and mean deliberation times as a function of the balance of reward associated with the two outcomes.

Fig. 2.

Peaks of activity-associated performance of the decision-making task compared to the visuomotor control task rendered onto the averaged MRI scans of the eight volunteer subjects used in the current study (threshold, p < 0.01).A, Peak of activation in orbitomedial PFC (BA 11);B, peak of activity within orbitolateral PFC (BA 10);C, activation within the inferior convexity (BA 47).

Fig. 3.

Increased rCBF from the two decision-making conditions compared with the visuomotor control task rendered onto a representative brain (threshold, p < 0.01).A, 4:2 condition − control task; B, 5:1 condition − control task. Note the lack of activity within dorsolateral areas of the PFC.