Abnormal functional connectivity strength in first-episode, drug-naïve adult patients with major depressive disorder.

•We used of the functional connectivity strength (FCS) measure which has not been used to the first-episode, drug-naïve adult patients with major depressive disorder.•We found reduced default mode network functional connectivity in patients with major depressive disorder.•The abnormalities of the DMN and cortico-limbic networks are closely related to emotional disorders and cognitive impairment in patients with depression.