Interhemispheric Symmetry in the Alpha Peak Before and After rTMS for Major Depressive Disorder

The purpose of this study is to investigate interhemispheric differences (or conversely, symmetry) in the EEG alpha wave in patients with major depressive disorder (MDD) and determine whether the alpha band interhemispheric symmetry changes due to repetitive transcranial magnetic stimulation (rTMS). Twenty patients (n=20) diagnosed with MDD underwent 36 sessions of rTMS. Surface electroencephalography (EEG) was acquired from each subject at baseline and after the 36 sessions of rTMS. Additionally, conventional clinical MDD assessments were conducted pre- and post-treatment and scores from the Montgomery-Asberg Depression Rating Scale (MADRS) questionnaire and the Generalized Anxiety Disorder Questionnaire (GAD-7) were also analyzed. The alpha peak amplitude and width were consistently symmetric across hemispheres pre-treatment and post-treatment both in the frontal and posterior regions (paired t-tests, p values were well above the .05 significance level). The alpha band peak frequency was also symmetric pre-treatment, but there were statistically significant interhemispheric differences in peak frequency post-treatment in the frontal region; the left-side peak frequency was on average 0.18 Hz lower than the right side (paired t-test, p=.02). Depression severity, as measured by MADRS, decreased with rTMS in all 20 subjects; anxiety also improved according to GAD-7 scores in all but one subject, whose score increased by 3 points. These improvements in clinical scores were not found to be correlated with any changes in symmetry. However, the interhemispheric difference in peak frequency post-treatment in the frontal region could implicate modulation of alpha peak frequency as a potential mechanism for treating depression through rTMS.