关键词: 奖励概率, 社会奖励, 金钱奖励, 抑郁倾向, 奖励敏感性

Abstract: Anhedonia is a core symptom of depression, so depressed people are thought to have a motivational disorder. Several studies have linked depression to decreased neuro sensitivity to monetary rewards, but there is no consistent conclusion as to whether reward passivation can be directly generalized to other types of rewards. Social reward, similar to monetary reward, is a driving force that shapes behavior. The reward probability will influence the individual's anticipation to reward, which in turn will directly affect individual's subsequent behavior. However, there is no study to systematically explore the influence of reward probability on the behavioral performance of depression-inclined individuals regarding different types of rewards. Therefore, this study explored the following three questions. (1) Is there a difference in the behavioral response of depression-inclined individuals in social and monetary reward tasks? (2) Whether reward (social/monetary) and incentive will elicit different behavioral responses in depression-inclined individuals compared to healthy control? (3) How does the reward probability influence the reward sensitivity of depression-inclined individuals on social and monetary rewards?
The four-factor mixed experimental design of 2 (reward type: monetary reward, social reward)×2(incentive type: incentive, non-incentive)×2(reward probability: high and low)×2(treatment group: depression inclination, health) was applied, in which only the treatment group was the between-subject variable. The dependent variable was the reaction time and hit rate. According to the Beck Depression Inventory-Ⅱ (BDI-Ⅱ) and Self-Rating Depression Scale (SDS) scores, 57 healthy participants (BDI-Ⅱ< 14 and SDS indices< .5) and 57 depression-inclined participants (BDI-Ⅱ> 14 and SDS indices> .5) were recruited. The monetary incentive delay task (MID) and social incentive delay task (SID) were administered to investigate the reward sensitivity of depression-inclined group and healthy control in monetary and social reward, in which the successful response is rewarded by money in RMB or "thumbs up" as a monetary reward or social reward respectively. Task difficulty was manipulated by varying the amount of time people had to respond to an item. In the easy condition, most of the items would be slow, all the items averagely appeared for 307.21±167.42ms, the performance standard was to get about 66% of the items correct (high reward probability); in the hard condition, most of the items would be fast, all the items averagely appeared for 251.04±164.47ms, the performance standard was to get about 33% of the items correct (low reward probability).
Behavioral results revealed that, under the incentive condition, the depression-inclined group had lower hit rate than healthy control, whereas there was no inter-group effect in the non-incentive condition. In the condition of high reward probability, the response time of the healthy control was significantly shorter than that of the depression-inclined group, but there was no inter-group effect in the condition of low reward probability.
The above behavioral results suggest that depression-inclined individuals are less sensitive to reward incentive, and the blunt reward functioning of depression inclination individuals generally exist in social reward and monetary reward. In addition, this bluntness is more obvious under the condition of high reward probability. Furthermore, the reward probability will affect the performance of individuals with depression inclination in different reward types, which may be related to the difficulty of the task and the uncertainty of the reward.

Key words: reward probability, social reward, monetary reward, depression inclination, reward sensitivity