Young girls at high risk for depression, but who have not experienced any symptoms, show differences in neural response patterns when processing the possibility of receiving a reward or sustaining a loss, according to a report in the April issue of Archives of General Psychiatry, one of the JAMA/Archives journals.
"A hallmark characteristic of major depressive disorder is the diminished experience of pleasure or reward," the authors write as background information in the article. "For example, compared with non-depressed persons, depressed individuals have been found to be characterized by attenuated [decreased] reactivity to slides depicting pleasant scenes, to amusing film clips, to pleasant drinks and to monetary reward contingencies." Recent research has suggested that these variations are reflected in underlying differences in the way the brain processes pleasant stimuli.
To begin assessing whether these deficits precede the onset of depression or are a consequence of the disorder, Ian H. Gotlib, Ph.D., of Stanford University, Calif., and colleagues studied 13 10- to 14-year-old girls who did not have depression themselves but whose mothers had recurrent depression (high-risk group). They were compared with 13 girls who were the same age but had no personal or family history of depression (low-risk group).
All 26 participants underwent functional magnetic resonance imaging (fMRI) while completing a task involving the possibility of reward and punishment. They were first shown a target and told that if a circle appeared, they could gain points by being fast enough to hit the target. If a square appeared, they could avoid losing points by hitting the target quickly. If a triangle appeared, they could neither win nor lose points and should avoid responding. The task consisted of 100 six-second trials, each of which contained an anticipation phase and a feedback phase, during which the girls were told whether they gained or lost points. The points could be redeemed for prizes at the end of the task.
The images revealed important differences in the way the two groups responded to the task. The high-risk group displayed diminished neural responses during both anticipation and receipt of the reward when compared with the low-risk group. Specifically, they did not show any activation in a brain area known as the dorsal anterior cingulate cortex, which appears to be involved in reinforcing past experiences to facilitate learning. However, compared with low-risk girls, high-risk girls showed an increased activation in this area when receiving punishment. This suggests they may more easily integrate information about loss and punishment than reward and pleasure over time.
"Considered together with reduced activation in the striatal areas commonly observed during reward, it seems that the reward processing system is critically impaired in daughters who are at elevated risk for depression, although they have not yet experienced a depressive episode," the authors conclude. "Clearly, longitudinal studies are needed to determine whether the anomalous activations observed in this study during the processing of rewards and losses are associated with the subsequent onset of depression."
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