Resting electroencephalographic correlates of the clinical response to repetitive transcranial magnetic stimulation: A preliminary comparison between unipolar and bipolar depression

- Baseline EEG can predict clinical response to rTMS in MDD and BP patients.
- Delta/theta and alpha oscillations that predict the therapeutic response are generated by different brain regions.
- Frontal lobe oscillatory power in theta and beta bands is higher in BP than in MDD patients.

BackgroundMajor depressive disorder (MDD) and bipolar disorder (BP) are two different types of mood disorders, sometimes difficult to distinguish from their depressive symptoms, and for which repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex (DLPFC) has been proposed to treat refractory patients. Here we studied whether the electroencephalogram (EEG) at rest could be used to predict the therapeutic response to left DLPFC 10 Hz rTMS, and to which extent BP and MDD patients show similar correlation between the clinical response and the cortical networks at rest.MethodsEight MDD (6 females) and 10 BP patients (6 females) were included. The rTMS therapy consisted of 10 to 20 neuronavigated sessions, with 2000 pulses continuously applied at 120% motor threshold for each session. RTMS sessions at the beginning, middle and end of the therapy were performed while recording EEG signals. EEG spectral power was partitioned using the common physiological frequency bands and was statistically analysed at the scalp level and after cortical source reconstruction.ResultsWe found significantly higher power in theta and beta bands in BP patients than in MDD patients, mainly localised in the prefrontal cortex. In addition, responders showed higher power in delta and theta bands in parietal regions and weaker frontal alpha power, when compared to non-responders.DiscussionThese preliminary findings on a small cohort suggest that pre-treatment EEG oscillatory patterns may have some predictive value regarding rTMS therapy, both for MDD and BP disorders.