Abstract
The evaluation of transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) promises valuable information about fundamental brain related mechanisms and may serve as a diagnostic tool for clinical monitoring of therapeutic progress or surgery procedures. However, reports about spontaneous fluctuations of MEP amplitudes causing high intra-individual variability have led to increased concerns about the reliability of this measure. One possible cause for high variability of MEPs could be neuronal oscillatory activity, which reflects fluctuations of membrane potentials that systematically increase and decrease the excitability of neuronal networks. Here, we investigate the dependence of MEP amplitude on oscillation power and phase by combining the application of single pulse TMS over the primary motor cortex with concurrent recordings of electromyography and electroencephalography. Our results show that MEP amplitude is correlated to alpha phase, alpha power as well as beta phase. These findings may help explain corticospinal excitability fluctuations by highlighting the modulatory effect of alpha and beta phase on MEPs. In the future, controlling for such a causal relationship may allow for the development of new protocols, improve this method as a (diagnostic) tool and increase the specificity and efficacy of general TMS applications.
Highlights
Transcranial magnetic stimulation (TMS) allows for a non-invasive investigation of corticospinal excitability
This larger study consisted of two identical experimental sessions in which intermittent theta burst stimulation (iTBS) was applied to participants at rest before motor evoked potentials (MEPs) changes to baseline were measured for sixty minutes and one control visit in which iTBS was replaced with sham-iTBS
Averaged Pearson linear correlations from EEG channels C3, FC1, FC5, CP1 and CP5 were performed between logarithmic power and both MEP amplitudes and permutated MEP amplitudes for frequencies between 2Hz and 30Hz in steps of 0.5Hz
Summary
We aim to provide further insight into the relationship of the power and phase of alpha and beta oscillations with MEP amplitude as a representative measure of corticospinal excitability
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