Electroencephalography during repetitive transcranial magnetic stimulation could be a key to personalized treatment: a methodological inspection in the frequency domain

Background and aims: Repetitive transcranial magnetic stimulation (rTMS) has analgesic effects in acute and some chronic pain conditions. But not all patients benefit from it similarly. Brain activity changes based on electroencephalography (EEG) before and after rTMS treatment could hold a key to predicting treatment response. Here, we provided a feasibility study to obtain valid EEG signals during rTMS aiming at tracking neuromarkers of brain response to therapy.

Methods: In ten healthy participants, 64-channel EEG was recorded with a TMS-compatible system (g.tec, Austria) with 10Hz rTMS (3000 pulses) in two conditions: rest-EEG and during 10Hz rTMS to the primary motor cortex (M1). Each block of 100 TMS pulses took 10s (rTMS-EEG) followed by a 20s non-stimulation interval (rest-EEG). After removal of the TMS-induced decay artefact from the EEG and preprocessing, 64x64 channel matrices of magnitude spectrum coherence representing inter-electrode interactions were extracted for comparison between rTMS and rest-EEG conditions. The differences in EEG behaviour in rTMS and rest-EEG were also visually inspected using a Time-frequency spectrogram.

Results: The rest-EEG and rTMS-EEG coherence matrices were similar and comparable, indicating rTMS-EEG has the structural basis of rest-EEG (p>0.20). Time-frequency spectrogram of signals also shows hotspots at harmonics of the 10Hz rTMS, which are only evident during rTMS-EEG due to brain response to the 10Hz stimulus.

Conclusions: It is feasible to obtain EEG signals during rTMS at 10Hz to M1, comparable to the post-non-TMS period, which could be a key to estimating connectivity changes predictive of therapeutic outcome.