Patients with increased functional connectivity between the brain’s different regions who had also experienced childhood trauma had a subtype of depression that was non-responsive to treatment by SSRIs drugs. Specifically, the brain’s functional connectivity in regions involving the angular gyrus — played a large role in determining whether SSRIs were effective in treating depression.

On the other hand, the other two subtypes — where the participants’ brains did not show increased connectivity among its different regions or where participants had not experienced childhood trauma — tended to respond positively to treatments using SSRIs drugs. (Source: psychcentral.com)