Does pericentral mu-rhythm “power” corticomotor excitability? – A matter of EEG perspective

Abstract

Background: Electroencephalography (EEG) and single-pulse transcranial magnetic stimulation (spTMS) of the primary motor hand area (M1-HAND) have been combined to explore whether the instantaneous expression of pericentral mu-rhythm drives fluctuations in corticomotor excitability, but this line of research has yielded diverging results. Objectives: To re-assess the relationship between the mu-rhythm power expressed in left pericentral cortex and the amplitude of motor potentials (MEP) evoked with spTMS in left M1-HAND. Methods: 15 non-preselected healthy young participants received spTMS to the motor hot spot of left M1-HAND. Regional expression of mu-rhythm was estimated online based on a radial source at motor hotspot and informed the timing of spTMS which was applied either during epochs belonging to the highest or lowest quartile of regionally expressed mu-power. Using MEP amplitude as dependent variable, we computed a linear mixed-effects model, which included mu-power and mu-phase at the time of stimulation and the inter-stimulus interval (ISI) as fixed effects and subject as a random effect. Mu-phase was estimated by post-hoc sorting of trials into four discrete phase bins. We performed a follow-up analysis on the same EEG-triggered MEP data set in which we isolated mu-power at the sensor level using a Laplacian montage centered on the electrode above the M1-HAND. Results: Pericentral mu-power traced as radial source at motor hot spot did not significantly modulate the MEP, but mu-power determined by the surface Laplacian did, showing a positive relation between mu-power and MEP amplitude. In neither case, there was an effect of mu-phase on MEP amplitude. Conclusion:The relationship between cortical oscillatory activity and cortical excitability is complex and minor differences in the methodological choices may critically affect sensitivity.

The phase of sensorimotor mu and beta oscillations has the opposite effect on corticospinal excitability

“…Subject-level positive correlations were observed in majority of subjects. Although the observed relationship was relatively weak -correlations varying between -0.1 and 0.3 -it is in line with previous observations (Bergmann et al, 2019;Karabanov et al, 2021;Schilberg et al, 2021;Thies et al, 2020). However, others have found no relationship between mu power and MEP amplitude (Berger et al, 2014;Zrenner et al, 2018), or even a negative association (Madsen et al, 2019;Sauseng et al, 2009, Zarkowski et al, 2006.…”

“…Based on this, first pursuits on real-time detection of motor oscillation phase relationships in healthy volunteers have focused on the mu rhythm (Bergmann et al, 2019;Madsen et al, 2019;Schaworonkow et al, 2018;2019;Zrenner et al, 2018), Various studies suggest that motor evoked potential (MEP) amplitude is larger at the trough of the mu rhythm and smaller at the peak (Bergmann et al, 2019;Desideri et al, 2019;Schaworonkow et al, 2018;2019;Zrenner et al, 2018). However, others have provided evidence that ongoing mu phase does not significantly predict corticospinal excitation (Karabanov et al, 2021;Madsen et al, 2019). Rather, pre-stimulation mu power is suggested to determine MEP amplitude (Bergmann et al, 2019;Karabanov et al, 2021;Madsen et al, 2019;Thies et al, 2020).…”

“…Recent advances in real-time tracking of cortical oscillations and non-invasive modulation of motor cortex activity in healthy human participants have provided new insights (Bergmann et al, 2019;Madsen et al, 2019;Sasaki et al, 2021;Schaworonkow et al, 2018;2019;Shirinpour et al, 2020;Zrenner et al, 2016;. Such real-time systems, combining electroencephalography (EEG) and transcranial magnetic stimulation (TMS), have provided evidence for a modulation of corticospinal excitability by motor cortical oscillatory phase and power (Bergmann et al, 2019;Karabanov et al, 2021;Madsen et al, 2018;Zrenner et al, 2018).…”

“…However, others have provided evidence that ongoing mu phase does not significantly predict corticospinal excitation (Karabanov et al, 2021;Madsen et al, 2019). Rather, pre-stimulation mu power is suggested to determine MEP amplitude (Bergmann et al, 2019;Karabanov et al, 2021;Madsen et al, 2019;Thies et al, 2020).…”

The phase of sensorimotor mu and beta oscillations has the opposite effect on corticospinal excitability

“…Recent advances in real-time tracking of cortical oscillations and non-invasive modulation of motor cortex activity in healthy human participants have provided new insights [19e29]. Such real-time systems, combining electroencephalography (EEG) and transcranial magnetic stimulation (TMS), have provided evidence for a modulation of corticospinal excitability by motor cortical oscillatory phase and power [19,20,24,27].…”