Fig. 1.
Study selection process. *The studies by Petty and Schlesser39 and Petty and colleagues41 were included in analyses of unipolar and bipolar disorders. **Studies by Gerner and colleagues,33 Kasa and colleagues,35 Mann and colleagues37 and Post and colleagues50 were incuded in analyses of unipolar and bipolar disorders. †The study by Bhagwagar and colleagues21 was included in analyses of unipolar and bipolar disorders. CSF = cerebrospinal fluid; GABA = γ-aminobutyric acid; MDE = major depressive episode; MRS = magnetic resonance spectroscopy.