Distributed neural representation of expected value

Abstract

Anticipated reward magnitude and probability comprise dual components of expected value (EV), a cornerstone of economic and psychological theory. However, the neural mechanisms that compute EV have not been characterized. Using event-related functional magnetic resonance imaging, we examined neural activation as subjects anticipated monetary gains and losses that varied in magnitude and probability. Group analyses indicated that, although the subcortical nucleus accumbens (NAcc) activated proportional to anticipated gain magnitude, the cortical mesial prefrontal cortex (MPFC) additionally activated according to anticipated gain probability. Individual difference analyses indicated that, although NAcc activation correlated with self-reported positive arousal, MPFC activation correlated with probability estimates. These findings suggest that mesolimbic brain regions support the computation of EV in an ascending and distributed manner: whereas subcortical regions represent an affective component, cortical regions also represent a probabilistic component, and, furthermore, may integrate the two.

Figure 1.

Probabilistic monetary-incentive delay-task trial structure.

Figure 2.

Group maps of regions whose activation correlates with the linear model of expected value. Warm colors signify activation, whereas cool colors signify deactivation (threshold, p < 10^-5). A, Anterior; L, left.

Figure 3.

Group maps of contrasts related to distinct terms of expected value. Maps illustrate the interaction of VAL by MAG(V), the main effect of PRB (P), and the interaction of VAL by MAG by PRB (EV). Warm colors signify activation, whereas cool colors signify deactivation (threshold, p < 10^-5). A, Anterior; R, right.

Figure 4.

Peak percentage signal change by gain trial type for right VOIs. Bars represent means ± SEM (n = 14). Trial alignment (left to right) reflects expected value (low to high). Symbols indicate significant difference from the low (+, >$0.00) and middle (++, >$1.00 and >$0.00) magnitude incentive conditions, matched for valence and probability (within-subject pairwise comparisons; p < 0.005, corrected for 9 comparisons). ACing, Anterior cingulate. Error bars represent SEM.

Figure 5.

VOI time courses and functional correlations. A, Activation time courses taken from the right MPFC VOI for +$5.00 gain trials of varying probabilities (^*, 80 vs 20% probability of success; p < 0.05; two-tailed t test). B, Correlation of percentage hit estimate for high- versus low-probability trials with percentage signal change in the right MPFC VOI for high- versus low-probability +$5.00 gain trials (lag, 4 s; r = 0.51; p < 0.05; one-tailed). C, Activation time courses taken from the right NAcc VOI for gain trials of varying magnitudes (^**, +$5.00 vs +$1.00 and +$0.00; ^*, $1.00 vs $0.00; p < 0.05; two-tailed t test). D, Correlation of self-reported positive arousal in response to +$5.00 cues with percentage signal change in the right NAcc VOI in response to +$5.00 cues (lag, 4 s; r = 0.52; p < 0.05; one-tailed). ant, Anticipation; rsp, response; Prob, probability; MD, mean-deviated. Error bars represent SEM.