title: Cortical brain states and corticospinal synchronization influence TMS-evoked motor potentials.
abstract: Transcranial magnetic stimulation (TMS) influences cortical processes. Recent findings indicate, however, that, in turn, the efficacy of TMS depends on the state of ongoing cortical oscillations. Whereas power and phase of electromyographic (EMG) activity recorded from the hand muscles as well as neural synchrony between cortex and hand muscles are known to influence the effect of TMS, to date, no study has shown an influence of the phase of cortical oscillations during wakefulness. We applied single-pulse TMS over the motor cortex and recorded motor-evoked potentials along with the electroencephalogram (EEG) and EMG. We correlated phase and power of ongoing EEG and EMG signals with the motor-evoked potential (MEP) amplitude. We also investigated the functional connectivity between cortical and hand muscle activity (corticomuscular coherence) with the MEP amplitude. EEG and EMG power and phase in a frequency band around 18 Hz correlated with the MEP amplitude. High beta-band (∼34 Hz) corticomuscular coherence exhibited a positive linear relationship with the MEP amplitude, indicating that strong synchrony between cortex and hand muscles at the moment when TMS is applied entails large MEPs. Improving upon previous studies, we demonstrate a clear dependence of TMS-induced motor effects on the state of ongoing EEG phase and power fluctuations. We conclude that not only the sampling of incoming information but also the susceptibility of cortical communication flow depends cyclically on neural phase.
authors.affiliation: International Laboratory for Brain, Music, and Sound Research (BRAMS), Department of Psychology, University of Montréal, Canada;
authors.forename: Julian
authors.initials: J
authors.lastname: Keil
authors.forename: Jana
authors.initials: J
authors.lastname: Timm
authors.forename: Iria
authors.initials: I
authors.lastname: Sanmiguel
authors.forename: Hannah
authors.initials: H
authors.lastname: Schulz
authors.forename: Jonas
authors.initials: J
authors.lastname: Obleser
authors.forename: Marc
authors.initials: M
authors.lastname: Schönwiesner
mesh_terms: D000293:Adolescent; D000328:Adult; D004569:Electroencephalography; D019054:Evoked Potentials, Motor; D005260:Female; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation
keywords: EEG; EMG; corticospinal coherence; phase; power