Intermittent Theta Burst Stimulation to the Primary Motor Cortex Reduces Cortical Inhibition: A TMS-EEG Study

Abstract

Introduction: The aim of this study was to reveal the effects of intermittent theta burst stimulation (iTBS) in modulating cortical networks using transcranial magnetic stimulation and electroencephalography (TMS-EEG) recording. Methods: Eighteen young adults participated in our study and received iTBS to the primary motor cortex (M1), supplementary motor area, and the primary visual cortex in three separate sessions. A finger tapping task and ipsilateral single-pulse TMS-EEG recording for the M1 were administrated before and after iTBS in each session. The effects of iTBS in motor performance and TMS-evoked potentials (TEPs) were investigated. Results: The results showed that iTBS to the M1, but not supplementary motor area or the primary visual cortex, significantly reduced the N100 amplitude of M1 TEPs in bilateral hemispheres (p = 0.019), with a more prominent effect in the contralateral hemisphere than in the stimulated hemisphere. Moreover, only iTBS to the M1 decreased global mean field power (corrected ps < 0.05), interhemispheric signal propagation (t = 2.53, p = 0.030), and TMS-induced early α-band synchronization (p = 0.020). Conclusion: Our study confirmed the local and remote after-effects of iTBS in reducing cortical inhibition in the M1. TMS-induced oscillations after iTBS for changed cortical excitability in patients with various neurological and psychiatric conditions are worth further exploration.

Intermittent Theta Burst Stimulation Increases Natural Oscillatory Frequency in Ipsilesional Motor Cortex Post-Stroke: A Transcranial Magnetic Stimulation and Electroencephalography Study

“…In the time domain, we did not observe any significant change in LMFP or GMFP after iTBS. Several studies have investigated acute adaptations in LMFP and GMFP after iTBS applied on M1 in healthy adults, but the results lack a common thread ( Gedankien et al, 2017 ; Bai et al, 2021 ; Ozdemir et al, 2021 ). No significant change in LMFP or GMFP after iTBS was observed in some studies ( Gedankien et al, 2017 ; Ozdemir et al, 2021 ), but a reduction in GMFP after iTBS was reported in a recent study ( Bai et al, 2021 ).…”

“…As TEP main peaks are not always present in stroke survivors, LMFP and GMFP have the advantage of quantifying TEPs in stroke studies ( Tscherpel et al, 2020 ). The acute adaptations in LMFP and GMFP after iTBS have been investigated in healthy adults, but results remain inconsistent in current literature ( Gedankien et al, 2017 ; Bai et al, 2021 ; Ozdemir et al, 2021 ). Some studies reported no change in LMFP or GMFP after iTBS ( Gedankien et al, 2017 ; Ozdemir et al, 2021 ), while one study reported reduced GMFP after iTBS ( Bai et al, 2021 ).…”

“…The acute adaptations in LMFP and GMFP after iTBS have been investigated in healthy adults, but results remain inconsistent in current literature ( Gedankien et al, 2017 ; Bai et al, 2021 ; Ozdemir et al, 2021 ). Some studies reported no change in LMFP or GMFP after iTBS ( Gedankien et al, 2017 ; Ozdemir et al, 2021 ), while one study reported reduced GMFP after iTBS ( Bai et al, 2021 ). The adaptations in LMFP and GMFP after iTBS have not been investigated in stroke survivors.…”

“…Time-frequency domain analysis offers possibility to study the functional specificity of cortical oscillations in each frequency band [i.e., evoked oscillatory response (EOR)] ( Thut and Miniussi, 2009 ). The adaptations in EOR after iTBS have been investigated in healthy adults, but results were inconsistent ( Casula et al, 2016 ; Chung et al, 2017 ; Bai et al, 2021 ). One study reported a reduction in alpha band EOR after iTBS ( Bai et al, 2021 ), while some studies reported an increase in theta ( Chung et al, 2017 ) or beta ( Casula et al, 2016 ) band EOR after iTBS.…”

“…The adaptations in EOR after iTBS have been investigated in healthy adults, but results were inconsistent ( Casula et al, 2016 ; Chung et al, 2017 ; Bai et al, 2021 ). One study reported a reduction in alpha band EOR after iTBS ( Bai et al, 2021 ), while some studies reported an increase in theta ( Chung et al, 2017 ) or beta ( Casula et al, 2016 ) band EOR after iTBS. Besides EOR, time-frequency domain analysis also allows for the study of natural frequency (i.e., the frequency with the maximal power in a specific brain region) ( Tremblay et al, 2019 ).…”