In Depression, Conflict May Accompany Thoughts of a Reward
> 3/26/2008 12:06:57 PM

A diminishment in positive emotions in often one of the most difficult aspects of depression, a symptom signifying that a depressed individual's experience of positive stimuli may differ substantially from the experiences of someone without depression. We still don't have a complete view of the influences and implications of this symptom, but with the results of a recent study, researchers from Stanford University add to our growing knowledge. In studying a group of individuals anticipating a reward, they observed some differences in patterns of brain activity between people with depression and those without.

In their study, which appears in the April issue of Biological Psychiatry, the researchers designed a task to identify the neural responses of subjects anticipating a gain or a loss. They tested 14 individuals with major depressive disorder and 12 controls. To ensure that differences between the two groups could not be attributed to the effects of medication, none of the study's participants were taking psychotropic medication, including antidepressants. While undergoing fMRI scans, the subjects were briefly presented with a white target and attempted to push a button during the target's appearance. By correctly pushing the button, they would either receive a monetary reward (from $0 to $5) or avoid losing a comparable sum of money. A signal appeared prior to each target, alerting participants as to whether they could potentially gain or potentially lose money during the next trial and identifying the amount of money at stake.

The two groups performed similarly on the task, and their neural responses also revealed some important similarities. While anticipating a gain, both depressed and control subjects experienced increased activity in the nucleus accumbens (NAcc), an area of the brain important in processing rewards, and the amount of NAcc activity did not differ substantially between the two groups. This was a surprising result for the researchers, who had hypothesized that reduced NAcc activity would occur in depressed individuals anticipating a reward. In addition, when asked to report their emotional states, the emotional experience of depressed subjects resembled that of control subjects. Both groups reported an increase in positive emotions when expecting to receive money.

In other important ways, however, the two groups did differ from one another. When expecting a monetary reward, subjects with depression experienced increased activity in the dorsal anterior cingulate cortex (ACC). Previously implicated in the management of internal conflict and uncertainly, this area of the brain can become active during situations in which we could make mistakes. Tellingly, the control subjects also experienced increased activity in the dorsal ACC, but only when they anticipated losing money. These findings indicate that individuals with depression do experience positive feelings while anticipating a reward, but their pleasure is interwoven with the negative feelings that individuals without depression experience when anticipating a loss.

A diminishment in positive emotions is a key component of depression and, the authors of this study suggest, experiencing conflict while anticipating a reward may represent a substantial barrier to recovery. Further research of the neural pathways involved in reward processing may yield a clearer understanding of how individuals with depression respond to positive stimuli. And by continuing this line of research, researchers may be able to develop more effective forms of treatment to help those who struggle from depression improve their mental well-being.

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