Activity in the amygdala elicited by unfair divisions predicts social value orientation

Abstract

'Social value orientation' characterizes individual differences in anchoring attitudes toward the division of resources. Here, by contrasting people with prosocial and individualistic orientations using functional magnetic resonance imaging, we demonstrate that degree of inequity aversion in prosocials is predictable from amygdala activity and unaffected by cognitive load. This result suggests that automatic emotional processing in the amygdala lies at the core of prosocial value orientation.

Figure 1

Task design and behavior. (a) Triple-Dominance measure task. Subjects chose one of three alternatives: prosocial (1), individualistic (2) and competitive (3) distributions of money between the self and the unknown other. (b) Reward pair evaluation task. (c) Comparison of model’s three regression coefficients (W_D , W_Rs, and W_Ro for the absolute value or difference, the self reward and the other reward, respectively) between prosocials and individualists. For behavioral data, error bar means standard deviation over subjects.

Figure 2

Difference between prosocials and individualists in the correlation of brain activity with the absolute value of reward difference D_a. (a) coronal section of the right amygdala where the two groups showed a significant difference in correlation with the absolute value of reward difference D_a. (MNI coordinates 20, −2, −12). (b) BOLD signal increase at the amygdala peak during 12 trials with the largest D_as (solid line) and 12 trials with the smallest D_as (dotted line) for prosocials and individualists. Time 0 specifies the presentation of reward pair. Error bar means standard deviation over subjects. (c) Left: Beta values of each prosocial (grey) and individualist (black) in correlation with D_a. Right: correlation of each subject’s beta value and W_D (the subject’s dislike of D_a) (grey: prosocials, black: individualists). A t-test was conducted to determine whether the regression coefficient was significantly different from 0.

Figure 3

Results of reward pair evaluation task with cognitive load. (a) Comparison of W_D (the subject’s dislike of the absolute value of reward difference Da) between prosocials and individualists in unloaded (left) and loaded (right) conditions.