題目： Depressive mood and discounting of delayed monetary gains and losses
担当教員： ラドフォード・マーク H.B.
Previous studies have reported that brain serotonin level has an important role in depression and impulsivity. Furthermore, recent studies have focused on the concept of “delay discounting” as one subcomponent of impulsivity, and has showed that a reduction in brain serotonin levels is accompanied by an increase in degree of delay discounting.
Furthermore, some depressed patients appear to be impulsive. For example, although not all, some patients display suicidal behavior, which has been described as a form of impulsive behavior.
In this study, we investigated the relationship between depression and impulsivity. We operationally defined impulsivity as ‘degrees of delay discounting for gains and losses’. Our hypothesis was that psychiatrically depressed patients discount future gains and losses more than healthy controls.
In study 1, we recruited healthy university students as controls. Participants completed a scale which measures depressive tendency (Beck’s Depression Inventory; BDI) and scales which measure degrees of delay discounting of gains and losses (Kirby’s Monetary Questionnaire). The results showed an association between depressive tendency and degrees of delay discounting for gains and losses only in females.
In study 2, we examined depressed patients. The results showed that there are moderate correlations between depressive tendency and degrees of delay discounting in both male and female patients, although these correlations were not significant because of the small sample size.
In study 3, we compared degrees of delay discounting between depressed patients and healthy university students. The results showed that depressed patients discount future gains more than university students, whereas depressed patients discount future losses less than university students.
Our results suggest that there is a relationship between depressive tendency and impulsivity, but that the nature of the relationship may be complex. There is also some evidence to suggest there may be sex differences in the relationship.
Some possible factors, which appeared to affect our results, and the implications of this study are discussed.