Cortical mechanisms underlying variability in intermittent theta-burst stimulation-induced plasticity: A TMS-EEG study.

Objective: To test the hypothesis that intermittent theta burst stimulation (iTBS) variability depends on the ability to engage specific neurons in the primary motor cortex (M1).
Methods: In a sham-controlled interventional study on 31 healthy volunteers, we used concomitant transcranial magnetic stimulation (TMS) and electroencephalography (EEG). We compared baseline motor evoked potentials (MEPs), M1 iTBS-evoked EEG oscillations, and resting-state EEG (rsEEG) between subjects who did and did not show MEP facilitation following iTBS. We also investigated whether baseline MEP and iTBS-evoked EEG oscillations could explain inter and intraindividual variability in iTBS aftereffects.
Results: The facilitation group had smaller baseline MEPs than the no-facilitation group and showed more iTBS-evoked EEG oscillation synchronization in the alpha and beta frequency bands. Resting-state EEG power was similar between groups and iTBS had a similar non-significant effect on rsEEG in both groups. Baseline MEP amplitude and beta iTBS-evoked EEG oscillation power explained both inter and intraindividual variability in MEP modulation following iTBS.
Conclusions: The results show that variability in iTBS-associated plasticity depends on baseline corticospinal excitability and on the ability of iTBS to engage M1 beta oscillations.
Significance: These observations can be used to optimize iTBS investigational and therapeutic applications.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)