Reduced Response to Rewards Predicts Depression in Teenagers



Depression among teenagers has been the focus of much attention over the past decade, and the growing rates of it—along with its associated heightened risk of suicide and substance abuse—have been alarming. The better it can be predicted who is at highest risk, the more that effective prevention strategies can be targeted toward those high-risk teens.

So far, many of those predictive efforts have centered around behavioral, social, or environmental characteristics. While studying these areas is valuable in its own right, biology and genetics also play a significant potential role in depression risk. How do the brains of adolescents who are at high risk for depression behave differently than the brains of those who are at lesser risk? A recent study sheds light on the potential predictive power of something very specific in this realm: how the brain processes reward.

In a new study published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, researchers from the University of Calgary observed 145 teenagers, about 65% of them female, who had a history of depression or anxiety in their family. These families were part of a longitudinal study using brain imaging to look at risks for anxiety disorders and mood disorders in adolescent development.

Study participants played gambling-like games in which they were told that they had either won or lost, and their reward response was measured simultaneously during an EEG scan. Study participants who had a muted response to the reward of winning were more likely to have experienced a first depressive episode at either nine months or 18 months past the time of the initial brain scan. On the other hand, reward activity was not predictive of anxiety or suicidality.

Depression has many areas of symptomology: behavioral, physical, emotional, and cognitive. Emotionally, people suffering from depression tend to experience something called anhedonia: the loss of joy or pleasure, or the inability to enjoy things or find a spark that they might have had in the past before the depression. While many people believe that depression is solely about sadness, people who have suffered from it will often explain it more as a deadening of feeling, a disengagement, or a numbness—the loss of feeling those glimmers of light that not only bring excitement to our days, but can help bring a deeper sense of meaning to our lives.

So, it stands to reason that a lessened response to reward would go along with depression in this way. What is particularly interesting in this study is that the muted reward response predated the initial onset of depression symptoms. One could imagine several different causal scenarios. Does someone inherit a genetic predisposition toward a lower reward response, which over time means they get less joy from life, and eventually sink into anhedonia? Could it also be that people who have dampened reward responses tend to live their lives in such a way that a self-reinforcing cycle is created: they don’t find pleasure in certain activities that would help be protective against depression in the first place, like healthy social activity, outdoor time, intellectual or artistic endeavors, or meaningful hobbies? Could it be that if people are born with less of a propensity to find excitement or pleasure in rewards, then other people respond to them differently throughout their life, and they are more likely to be socially isolated or treated more negatively by others (which would be particularly potent as a trigger for depression in adolescents?). Finally, could it be that those who are genetically prone to lessened reward responses are more likely to have had parents with the same, and those parents raised them in such ways so as to make them more prone to depression?

An adolescent episode of depression—as much as it seems more common than ever—can have a lifetime of ripple effects, and confer even higher risk for later episodes. This study illuminates an important path for future study to explore, as it has potential implications for a way to identify those adolescents—or possibly even children—who could then most highly benefit from special interventions and supports to prevent their depression from ever happening in the first place. As the researchers in this study point out, there have so far been very few studies that have identified brain markers that are predictive of depression before the first signs of it start—so this study makes for some exciting findings indeed.


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