Most of us, just based on watching the people around us, have an intuitive sense that the word depression may be an umbrella term for something big that encompasses more than one thing.  Recently, Japanese researchers have found clues that point to three sub-types of depression, according to research published in Scientific Reports and summarized in Neuroscience News.  Using MRI technology and data from 134 individuals, researchers determined that individuals with depression and a history of trauma, and those without a history of trauma but increased connectivity among some of 78 different regions of the brain that were studied, formed the three sub-types. The research appears to have been geared toward determining who may and may not respond to SSRIs.

You can find the Neuroscience News summary here and the study itself here.