Sham-derived effects and the minimal reliability of theta burst stimulation

Theta-burst stimulation (TBS) is a patterned form of repetitive transcranial magnetic stimulation (rTMS) that has been used to induce long-term modulation ( plasticity ) of corticospinal excitability in a drastically shorter duration protocol than conventional rTMS protocols. In this study we tested...

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Bibliographic Details
Published in:	Scientific reports Vol. 11; no. 1; p. 21170
Main Authors:	Boucher, P. O., Ozdemir, R. A., Momi, D., Burke, M. J., Jannati, A., Fried, P. J., Pascual-Leone, A., Shafi, M. M., Santarnecchi, Emiliano
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 27-10-2021 Nature Publishing Group Nature Portfolio
Subjects:	631/378/1697/2601 631/378/2632/1694 Achievement tests Adolescent Adult Brain - physiology Evoked Potentials, Motor Excitability Female Humanities and Social Sciences Humans Long-Term Potentiation Magnetic fields Male Middle Aged Motor evoked potentials multidisciplinary Neuromuscular Junction - physiology Plasticity Pyramidal tracts Reproducibility of Results Science Science (multidisciplinary) Theta Rhythm Transcranial magnetic stimulation Transcranial Magnetic Stimulation - methods Transcranial Magnetic Stimulation - standards
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Summary:	Theta-burst stimulation (TBS) is a patterned form of repetitive transcranial magnetic stimulation (rTMS) that has been used to induce long-term modulation ( plasticity ) of corticospinal excitability in a drastically shorter duration protocol than conventional rTMS protocols. In this study we tested the reliability of the effects of two well defined TBS protocols, continuous TBS (cTBS) and intermittent TBS (iTBS), especially in relation to sham TBS, within and across the same 24 participants. All TBS protocols were repeated after approximately 1 month to assess the magnitude and reliability of the modulatory effects of each TBS protocol. Baseline and post-TBS changes in motor evoked potentials (MEP—measure of corticospinal excitability) amplitudes were compared across the cTBS, iTBS and sham TBS protocols and between the initial and retest visits. Overall, across participants, at the initial visit, iTBS facilitated MEPs as compared to baseline excitability, with sham eliciting the same effect. cTBS did not show a significant suppression of excitability compared to baseline MEPs at either visit, and even facilitated MEPs above baseline excitability at a single time point during the repeat visit. Otherwise, effects of TBS were generally diminished in the repeat visit, with iTBS and sham TBS replicating facilitation of MEPs above baseline excitability at similar time points. However, no protocol demonstrated consistent intra-individual modulation of corticospinal excitability upon retest. As the first study to test both iTBS and cTBS against sham TBS across repeat visits, our findings challenge the efficacy and reliability of TBS protocols and emphasize the importance of accounting for sham effects of TBS. Furthermore, given that therapeutic effects of TBS are hypothetically derived from consistent and repeated modulation of brain activity, the non-replicability of plasticity and sham effects call into question these basic mechanisms.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	2045-2322 2045-2322
DOI:	10.1038/s41598-021-98751-w