Social and monetary rewards in economic decision making – behavioral and neural findings

One of the most important questions in human and animal behavior is, without a doubt, the question of why we behave the way we do. A major aspect of the discussion can be narrowed down to the concept of motivation and incentives. That means that our behavior is often guided by the expectation of a positive reward, whether monetary or social. Thus, whenever a reward is available, it is assumed that we behave a particular way in order to receive it. One important field of research within neuroeconomics and behavioral economics is, therefore, the study of how changes in incentives can shape behavior and how social reward is integrated and valuated in our decision-making processes. Two main drivers—monetary and social reward—influence our behavior and decision making. On the one hand, we derive rewards from social interaction, and social considerations modulate decision making to a significant degree, e.g. sharing a good bottle of wine instead of drinking it alone. The pure value of a bottle of wine might be higher when I drink it alone because I get all the wine for myself. However, I might have a hangover on the next day. This fact might also affect my decision. It is likely that when I opt to share the bottle of wine with my dearest friends, I get less wine, but I also experience the wine as being more rewarding. Thus, although the absolute reward is lower, the subjective value is significantly higher, adding a social reward to the reward of the wine itself. Of course, sharing it with a friend is more rewarding than sharing it with a stranger. Thus, my willingness to forego a reward (that is, the wine) is dependent on the perceived social distance between me (the decision-maker) and the recipient. Overall, we make social decisions constantly and can consider them trade-offs between selfish goals and social considerations. At the same time, we often use monetary rewards to modulate behavior in favorable ways, for instance, bonus systems in companies and monetary incentives for good grades at school. The monetary incentive is likely to modulate the amount of effort that one puts into a good performance. Overall, these two reward systems can be considered the main drivers of human behavior. The two drivers demonstrate how rewards, either social or monetary, influence our behavior and show that these incentives are constantly present. I am investigating the effect of changes in these incentives in a series of three studies. In the first study, we remove and introduce monetary incentives, leading to changes in the motivation toperform well. We show that the changes in the incentives correlate with changes in BOLD activity in the ventral striatum. Thus, the BOLD activity increases when monetary incentives are introduced and decreases when monetary incentives are removed. Task-related activity does not alter in response to changes in incentives. We suggest that the reward system initiates the change in performance, leading to a different degree of engagement and motivation to perform. In the second study, we focus on the social aspect of reward processing and investigate a biologically plausible model of prosocial choice by applying a social discounting experiment to the fMRI scanner environment. By varying social distance and selfish reward magnitude, we show that the temporoparietal junction (TPJ) tracks the temptation to be selfish, suggesting that the TPJ balances prosocial and selfish considerations. Also, connectivity between the TPJ and the ventromedial prefrontal cortex (VMPFC), a region associated with subjective value computation, is higher for social decisions than for egoistic ones. We suggest that the TPJ modulates basic value signals in the VMPFC, upregulating the value of generous choices. Another open question in the decision sciences is that of how environmental distractions affect decision making, that is, prosocial choice behavior. Therefore, in the third study, we investigate the influence of cognitive load on social distance-dependent generosity. Previous research indicates ambiguous results for the effect of cognitive load. We suggest that the diverse findings could be explained using the social distance approach. While generosity decreases at closer social distances, generosity increases at larger social distances. The results indicate that this is indeed the case. However, men drive the effect. In fact, we find an interaction between the level of cognitive load and gender. With the studies I present in this dissertation, I contribute to the development of a multidimensional view of the processing of rewards in general and performance- based monetary and social distance-dependent social rewards in particular.