Diagnosis and subtyping of depressive disorders by quantitative electroencephalography: II. Interhemispheric measures are abnormal in major depressives and frequency analysis may discriminate certain subtypes.

Seventy-six inpatient RDC major depressives (51 primary and 25 secondary), drug free for at least ten days, and 93 normals were examined by quantitative electroencephalography (QEEG). Multivariate analyses of variance were performed on several diagnostic subgroups using QEEG variables identified in an earlier study as discriminators. Decreased interhemispheric coherence in the delta and/or theta frequency bands was present to a statistically significant degree in depressed subjects. Secondary major depressives showed a lesser decrease than did primary major depressives in both anterior and posterior brain regions. Depression secondary to organic brain syndrome was distinguished from other secondary depressions by the presence of significant slow wave excess in the former only. The ability of beta activity to discriminate unipolar from bipolar major depression was confirmed.