O16 Shifts in mean peak oscillatory frequency during repetitive transcranial magnetic stimulation (rTMS) treatment of major depressive disorder

Objectives Repetitive Transcranial Magnetic Stimulation (rTMS) is an effective treatment for Major Depressive Disorder (MDD). Efficacy is variable and there are no reliable predictors of treatment outcome. This study aimed to identify a quantitative electroencephalography (qEEG) biomarker of rTMS treatment outcome. Methods 59 subjects with MDD (mean baseline Inventory of Depressive Symptomatology – Self Rated [IDS-SR] score = 52) underwent rTMS treatment applied to left dorsolateral prefrontal cortex (DLPFC). Subjects were examined with a 64 channel TMS-compatible qEEG system before, during, and after the initial treatment session. Changes in primary and secondary mean peak frequencies between 6 and 14 Hz were examined between pre- and post-treatment resting states. Clinical outcome was examined after two and six weeks of treatment, with response defined as a 50% reduction in IDS-SR and remission a final IDS-SR ≤ 11. Results There was a significant association between changes in mean peak frequency and outcome. Early response and six -week remission were associated with acceleration and decreased variance of primary mean peak frequency, and emergence of higher frequency secondary peaks. Changes in mean peak frequency pre- to post- the initial rTMS treatment session predicted six-week clinical outcome. Discussion Changes in mean peak frequency during the initial rTMS treatment session are a promising biomarker of clinical outcome. Conclusions Future studies should examine shifts in frequency in relation to adjustment of rTMS parameters. Significance qEEG studies performed during the initial rTMS treatment session may be a useful method for guiding decisions regarding the duration and parameters used for rTMS treatment.