Are 5-HT Levels Increased in Depression?

In a recent paper, Andrews & Thomson (2009) presented the hypothesis that depression is a functional trait that was selected because it helps to solve complex problems and that it is related to high levels of serotonin in the brain. Notwithstanding the fact that the authors' main focus is on the first issue, the hypothesis ends up being much bolder in relation to the second one, as it challenges much about everything that is accepted by the scientific community in relation to the neurobiological basis of depression, as much as many of their own citations. As revealed in this paper, the studies cited by Andrews & Thomson (2009), in association with a compilation of the recent literature on the matter, suggest that serotonin levels vary from diminished to normal in the brain of non-medicated depressive patients without psychiatric or neurological comorbidities. Based on these studies, general lines of a new serotonergic hypothesis of depression (MDD) are introduced.