Research shows that the hippocampus is smaller in some depressed people. For example, in one fMRI study published in The Journal of Neuroscience, investigators studied 24 women who had a history of depression. On average, the hippocampus was 9% to 13% smaller in depressed women compared with those who were not depressed.
It is interesting to note that some adult wild-born macaques spontaneously exhibit depressive behaviors even though they have not been subjected to experimentally induced early-life stress (Camus et al. 2014; Shively et al. 1997; Willard and Shively 2012).
NHP studies show that experiences during development interact with underlying genetic and/or other physiologic profiles to alter known (and undoubtedly many unknown) aspects of the CNS, thereby predisposing individuals to depression later in life. This takes depression out of the realm of an emotional state and into the realm of organic disease, much like diabetes or cancer, whereby underlying predispositions are acted on by the environment to produce pathology.
Without antidepressants: About 20 to 40 out of 100 people who took a placebo noticed an improvement in their symptoms within six to eight weeks.
With antidepressants: About 40 to 60 out of 100 people who took an antidepressant noticed an improvement in their symptoms within six to eight weeks.
antidepressants improved symptoms in about an extra 20 out of 100 people