Reproducibility of the effects of theta burst stimulation on motor cortical plasticity in healthy participants

Abstract

Objective Theta-burst stimulation (TBS) is a repetitive transcranial magnetic stimulation (TMS) protocol, capable of enhancing or suppressing the amplitude of contralateral motor-evoked potentials (MEP) for several minutes after stimulation over the primary motor cortex. Continuous TBS (cTBS) produces a long-term depression (LTD)-like reduction of cortical excitability. The purpose of this study was to assess the test–retest reproducibility of the effects of cTBS and to investigate which neurophysiologic markers of cTBS-induced plasticity are most reproducible. Methods In ten healthy participants we evaluated in two different sessions the effects of cTBS (using AP–PA current direction, opposite to most commercial rTMS stimulators) on MEPs induced by single-pulse suprathreshold TMS (using AP–PA or PA current direction) over left motor cortex in the first dorsal inter-osseus (FDI) muscle. Results Results demonstrate that the marker of cTBS induced-plasticity with highest within-subject reproducibility is the modulation of corticospinal excitability measured 5 min after cTBS. Conclusion Overall the effects of cTBS modulation show limited test–retest reproducibility and some measures of the cTBS effects are more reproducible than others. Significance Studies comparing cTBS effects in healthy subjects and patients need to proceed with care. Further characterization of the effects of TBS and identification of the best metrics warrant future studies.

Efficacy and time course of paired associative stimulation in cortical plasticity: Implications for neuropsychiatry

“…For example, Vernet et al (2013) have shown that the effects of theta-burst stimulation effects waver over time, indicating that additional factors, such as fluctuations in attention, emotional state and arousal, interact with the TMS-induced changes on cortical excitability levels over time (Schutter et al, 2001;Vernet et al, 2013Vernet et al, , 2014Monte-Silva et al, 2009). Such oscillating patterns are also seen in some PAS studies (Grundey et al, 2012a;Kuo et al, 2007;Nitsche et al, 2009).…”

Interindividual variability in response to continuous theta-burst stimulation in healthy adults

“…It may be the case that choosing certain time points instead of the whole dataset can improve the sensitivity or robustness of the cluster analysis. One option may be to choose T5, previously found to be the most reliable time point for measuring MEP changes following cTBS (Vernet et al, 2014) and/or T10 to capture the peak effect of TBS, including for participants whose MEPs return rapidly to baseline levels, and perhaps one of the later time points, e.g., T40 and/or T50, to use their discriminatory power for classifying the cTBS aftereffects (present results) and for capturing the differential time of return of post-TBS MEP amplitudes to baseline levels between healthy and clinical populations (Oberman et al, 2010, 2012, 2014, 2016; Freitas et al, 2011b; McClintock et al, 2011). …”

Theta burst stimulation to characterize changes in brain plasticity following mild traumatic brain injury: A proof-of-principle study

“…The intensity was fixed at 80% of AMT. This paradigm was recently shown to induce significant suppression of MEPs in healthy controls (see Vernet et al, 2014). Before cTBS, two to three batches of 20 to 30 MEPs (60 in total) were acquired in response to stimulation over the optimal FDI location, at an intensity of 120% of RMT and a rate of approximately 0.1 Hz (a random jitter of ±1 s was introduced to avoid any training effects).…”