Clinical Round Table 5 - Reconceptualizing Depression as an Evolved Adaptation

Much of what the field believes about depression in humans (and learned helplessness in animals) likely is wrong. Our clinical round table addresses each of the following: 1) unipolar depression is neither a disease nor a disorder but an evolved adaptation that is so prevalent as to be "species typical"; 2) depression evolved to facilitate thinking analytically in the service of solving complex problems (the analytical rumination hypothesis), with serotonin transmission actually elevated (not deficient) during depression in a fashion that allocates energy toward cognition; 3) animals exposed to inescapable stressors do not learn “helplessness”; rather, those exposed to escapable stressors learn a generalized expectation of control (resilience), mediated by cortical inhibition of serotonergic brainstem responses, that immunizes them against the effects of future stress; 4) antidepressant medications do not correct a deficit in neurotransmitter in the synapse but instead drive already-elevated serotonin so high that underlying homeostatic mechanisms push back—suppressing symptoms at the expense of keeping patients in episode and at elevated risk of relapse upon discontinuation; and 5) cognitive behavior therapy works by teaching patients to ruminate more efficiently, facilitating the problem-solving function that depression evolved to serve, and has an enduring effect (much like the immunizing effect of learned resilience in rodents) with evidence suggesting it produces enduring "top-down" cortical changes that are distinct from medications' "bottom-up" suppression of serotonergic-driven symptoms. From an evolutionary perspective, depression is not the problem, it is the beginning of a search for a solution to whatever problem(s) triggered the distress, and serotonin is the mechanistic “through-line” that connects the disparate aspects of its reconceptualization. It is a basic principle of evolutionary medicine that any intervention that facilitates the function that an adaptation evolved to serve (as cognitive behavior therapy appears to do) is to be preferred over the one (like the antidepressant medication) that merely anesthetizes the distress.