Does intermittent theta burst stimulation change oscillatory activity in the targeted left dorsolateral prefrontal cortex? - a resting-state EEG study

Abstract Background: The repeated delivery of intermittent theta burst stimulation (iTBS) to left dorsolateral prefrontal cortex (DLPFC) has been shown to improve depressive symptoms in patients with treatment-resistant depression. While alteration in brain oscillatory activity, measured by electroencephalography (EEG), has been suggested as potential mechanism of action, it is unclear whether a single session of prefrontal iTBS alters oscillatory activity in left DLPFC. Methods: We continuously recorded three minutes of resting-state EEG (rsEEG) three times before (pre) and five times after (post) a 10-min iTBS intervention (2s on - 8s off) in 13 healthy subjects. Stimulation targeted the left DLPFC under stereotactic guidance based on the subjects' structural MRI. For each recording epoch, we estimated the spectral power of the EEG signal from the scalp electrode that was closest to the stimulation within the theta, alpha, and beta band. We calculated the average power of each pre-defined frequency band pooling all pre-iTBS and all post-iTBS measurements of the participants. Pre-iTBS and post-iTBS data were separately compared for each frequency band using a Wilcoxon test (p<0.0167). Results: In our data, we did not observe statistical difference between expression of power in different bands before and after intervention (p > 0.0167). Moreover, the baseline expression of theta, alpha and beta activity as well as the relative change after iTBS showed large inter-individual variability. Conclusion: Our preliminary results suggest that iTBS of left DLPFC has no consistent neuromodulatory effect on the expression of resting-state oscillatory activity in the theta, alpha, and beta band. Results will be consolidated by increasing the sample size. Funding: This study is funded by the Innovation Fund Denmark (IFD) for the Grand Solution project “PRECISION-BCT” (Grant number: 9068-00025A). Research Category and Technology and Methods Basic Research: 10. Transcranial Magnetic Stimulation (TMS) Keywords: iTBS, EEG, DLPFC, Cortical oscillations