Depression has a wide variety of possible symptoms: sadness (of course), anhedonia (the inability to enjoy previously pleasurable activities), appetite change, guilt, fatigue, hypersomnia, and more. No two cases of depression are exactly the same, even though broad diagnoses are given to help doctors and patients think about the best way to handle treatment. Until now, the prevailing theory has been that different kinds of depression manifest because of differences in the brain-chemistry and personality of patients. A study in this issue of The American Journal of Psychiatry advances the alternative idea that it is not a difference in the patients that causes diverse depression patterns, but rather a difference in the adverse life events (ALEs) that these patients experience.
In 2006, Dr. Matthew Keller published evidence supporting the evolutionary-psychology interpretation of depression as an adaptive response. According to this theory, depression may seem exclusively maladaptive, but it is an appropriate response to some situations. If this is true, then depressed individuals should have different types of depression suited to the event that triggers them— feeling blue enough to hibernate during winter should look different than depression triggered by a mother’s funeral. In a study at the Virginia Institute for Psychiatric and Behavioral Genetics, 445 subjects did exhibit a pattern of depressive symptoms that corresponded to the trigger event.
This month, Dr. Keller followed up with ten times as many participants and a much more rigorous evaluation. He measured 12 different symptoms to look for patterns, and even a cursory look at the data reveals that many patterns do exist. Fear of the future triggered increased appetite but little guilt, a romantic breakup brought appetite loss, guilt, and trouble concentrating. The death of a loved one incited symptoms similar to the loss of a partner, but with anhedonia instead of guilt.
These patterns have strong statistical validity because they held their shape through many different categories. Age and gender did not weaken the link between a type of trigger and a type of depression. Between participants of different social classes and personalities, the same trigger was very likely to induce the same symptoms. Most importantly, there was a consistency between different depressive episodes in the same person. By following subjects for much longer than in his previous studies, and by asking about all depressive episodes that occurred, Dr. Keller discovered that a subject that experienced multiple episodes was likely to experience symptoms during each episode that corresponded to the closest trigger rather than to to the subject’s unique predisposition. Someone was not genetically fated to have guilt dominate their depression; rather, they felt guilt if the ALE was one that generally causes guilt. It is possible that certain people are more likely to experience certain ALEs, but this is unlikely. While certain personalities might be more likely to ruin a romantic relationship, it is doubtful whether any personality is more likely to suffer all of the other ALEs, for example the death of a loved one.
There are some other possible flaws in this study, but all of them are frankly discussed by the authors. Many of these can be dismissed because sufficient extra work is added to show that the concerns are not substantial. For example, the study did not originally differentiate between those who met the full diagnosis for Major Depression and those who merely displayed some of the symptoms. Realizing that some might argue that his patterns do not hold for true depression, Dr. Kelly reran all the numbers within just the Major Depression group and got the same results. One trouble that cannot be so easily dismissed is the fact that this study did not allow for participants to identify more than one ALE. A full 21% of subjects said that they felt that more than one event combined to cause their depression, but this interaction was not taken into account and there was no data collected on all the secondary ALEs that may have broken the camel’s back.
Any flaws in this study are gaps that can be filled later rather than corruptions of data or logic. It is clear that the symptoms of depression do depend, if not exclusively then at least to a large degree, upon the event that triggers the episode. This is something that therapists may have noticed from the anecdotal evidence of their own experience, but this study of thousands brings all of the patterns into clear focus. As the link between event and symptom becomes clearer, treatment will become more focused and standardized, and both doctors and patients will have a better understanding of what to expect after a tragedy.
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