Anticipation of monetary and social reward differently activates mesolimbic brain structures in men and women

Abstract

Motivation for goal-directed behaviour largely depends on the expected value of the anticipated reward. The aim of the present study was to examine how different levels of reward value are coded in the brain for two common forms of human reward: money and social approval. To account for gender differences 16 male and 16 female participants performed an incentive delay task expecting to win either money or positive social feedback. fMRI recording during the anticipation phase revealed proportional activation of neural structures constituting the human reward system for increasing levels of reward, independent of incentive type. However, in men activation in the prospect of monetary rewards encompassed a wide network of mesolimbic brain regions compared to only limited activation for social rewards. In contrast, in women, anticipation of either incentive type activated identical brain regions. Our findings represent an important step towards a better understanding of motivated behaviour by taking into account individual differences in reward valuation.

Fig. 1

Experimental paradigm for the Monetary (MID) and the Social Incentive Delay Task (SID). Participants were asked to hit a button as fast as possible when a white target square appeared on the screen. To generate reward anticipation, target presentation was preceded by a cue signalling the reward that would be presented if the button was hit fast enough. Circle cues presented different levels of potential reward, while the triangle announced no outcome independent of reaction time.

Fig. 2

Mean reaction times to the reward signalling cues in the MID and the SID task. (A) Mean reaction times of all participants to the cues announcing potential monetary (dark grey columns) or social reward (light grey columns). Circles with one, two, and three bars announce increasing levels of potential reward, triangles represent no outcome. (B) Mean reaction times in the MID (dark grey columns) and the SID task (light grey columns), separated for men (left) and women (right). Error bars indicate the standard error of the mean (s.e.m). *P < 0.01 (paired t-test, two-tailed).

Fig. 3

Activation foci for male and female participants during MID and SID linear anticipation. Brain areas increasingly activated by anticipated increasing amounts of money (MID task, triangle < circle with one bar < circle with two bars < circle with three bars) are displayed in red, brain areas increasingly activated by anticipated increasing amounts of social approval (SID task, triangle < circle with one bar < circle with two bars < circle with three bars) are displayed in blue separated for men (left) and women (right). The activation maps (P < 0.001, uncorrected; minimal cluster size 10 voxels) are projected onto coronal slices (y = 6) of the T1-weighted SPM-template. In the SID task, male participants did not show any activation at the chosen threshold. (It has to be noted though that if the threshold was lowered to P < 0.01, uncorrected, activation of the left striatum could also be seen in men). Bars represent parameter estimates for the MID (red bars) and the SID task (blue bars) in ROIs for the right and left NAcc, separated for men (left) and women (right). Error bars indicate the standard error of the mean (SEM).