The effect of pulse shape in theta-burst stimulation: Monophasic vs biphasic TMS

Karen Wendt; Majid Memarian Sorkhabi; Charlotte J Stagg; Melanie K Fleming; Timothy Denison; Jacinta O'Shea

doi:10.1016/j.brs.2023.08.001

The effect of pulse shape in theta-burst stimulation: Monophasic vs biphasic TMS

Brain Stimul. 2023 Jul-Aug;16(4):1178-1185. doi: 10.1016/j.brs.2023.08.001. Epub 2023 Aug 4.

Authors

Karen Wendt¹, Majid Memarian Sorkhabi², Charlotte J Stagg³, Melanie K Fleming⁴, Timothy Denison⁵, Jacinta O'Shea⁶

Affiliations

¹ MRC Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX1 3TH, UK; Department of Engineering Science, University of Oxford, Oxford, OX1 3PJ, UK. Electronic address: karen.wendt@some.ox.ac.uk.
² MRC Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX1 3TH, UK.
³ MRC Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX1 3TH, UK; Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
⁴ Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
⁵ MRC Brain Network Dynamics Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX1 3TH, UK; Department of Engineering Science, University of Oxford, Oxford, OX1 3PJ, UK.
⁶ Wellcome Centre for Integrative Neuroimaging, Oxford Centre for Human Brain Activity (OHBA), University of Oxford Department of Psychiatry, Warneford Hospital, Warneford Lane, Oxford, UK.

Abstract

Background: Intermittent theta-burst stimulation (i) (TBS) is a transcranial magnetic stimulation (TMS) plasticity protocol. Conventionally, TBS is applied using biphasic pulses due to hardware limitations. However, monophasic pulses are hypothesised to recruit cortical neurons more selectively than biphasic pulses, predicting stronger plasticity effects. Monophasic and biphasic TBS can be generated using a custom-made pulse-width modulation-based TMS device (pTMS).

Objective: Using pTMS, we tested the hypothesis that monophasic iTBS would induce a stronger plasticity effect than biphasic, measured as induced increases in motor corticospinal excitability.

Methods: In a repeated-measures design, thirty healthy volunteers participated in three separate sessions, where monophasic and biphasic iTBS was applied to the primary motor cortex (M1 condition) or the vertex (control condition). Plasticity was quantified as increases in motor corticospinal excitability after versus before iTBS, by comparing peak-to-peak amplitudes of motor evoked potentials (MEP) measured at baseline and over 60 min after iTBS.

Results: Both monophasic and biphasic M1 iTBS led to significant increases in MEP amplitude. As predicted, linear mixed effects (LME) models showed that the iTBS condition had a significant effect on the MEP amplitude (χ² (1) = 27.615, p < 0.001) with monophasic iTBS leading to significantly stronger plasticity than biphasic iTBS (t (693) = 2.311, p = 0.021). Control vertex iTBS had no effect.

Conclusions: In this study, monophasic iTBS induced a stronger motor corticospinal excitability increase than biphasic within participants. This greater physiological effect suggests that monophasic iTBS may also have potential for greater functional impact, of interest for future fundamental and clinical applications of TBS.

Keywords: Motor plasticity; Pulse-width modulation based TMS; TMS pulse shape; Theta burst stimulation (TBS); Transcranial magnetic stimulation (TMS).

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Evoked Potentials, Motor / physiology
Humans
Motor Cortex* / physiology
Neuronal Plasticity / physiology
Neurons
Theta Rhythm / physiology
Transcranial Magnetic Stimulation* / methods

Abstract

Publication types

MeSH terms

Grants and funding