No trace of phase: Corticomotor excitability is not tuned by phase of pericentral mu-rhythm

• Published in: Brain stimulation Vol. 12; no. 5; pp. 1261 - 1270
• Main Authors: Madsen, Kristoffer Hougaard, Karabanov, Anke Ninija, Krohne, Lærke Gebser, Safeldt, Mads Gylling, Tomasevic, Leo, Siebner, Hartwig Roman
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2019
• Subjects: Adult; Brain Waves - physiology; EEG-Triggered phase targeting; Electroencephalography; Electroencephalography - methods; Electromyography - methods; Evoked Potentials, Motor - physiology; Female; Humans; Male; Motor Cortex - physiology; Mu rhythm; Pericentral oscillation; Temporal and spatial neuronavigation; Transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Young Adult; EEG-Triggered phase targeting; Pericentral oscillation; Electroencephalography; Transcranial magnetic stimulation; Temporal and spatial neuronavigation; Mu rhythm
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2019.05.005

The motor potentials evoked by transcranial magnetic stimulation (TMS) over the motor hand area (M1-HAND) show substantial inter-trial variability. Pericentral mu-rhythm oscillations, might contribute to inter-trial variability. Recent studies targeting mu-activity based on real-time electroencephalography (EEG) reported an influence of mu-power and mu-phase on the amplitude of motor evoked potentials (MEPs) in a preselected group with strong pericentral mu-activity. Other studies that determined mu-power or mu-phase based on post-hoc trial sorting according in non-preselected individuals were largely negative. To reassess if cortico-spinal activity is modulated by the mu-rhythm, we applied single-pulse TMS to the M1-HAND conditional on the phase of the intrinsically expressed pericentral mu-rhythm in 14 non-preselected healthy young participants. TMS was given at 0, 90, 180, and 270° of the mu-phase. Based on the absence of effects of mu-phase or mu-power when analyzing the mean MEP amplitudes, we also computed a linear mixed effects model, which included mu-phase, mu-power, inter-stimulus interval (ISIs) as fixed effects, treating the subject factor as a random effect. Mixed model analysis revealed a significant effect of mu-power and ISI, but no effect of mu-phase and no interactions. MEP amplitude scaled linearly with lower mu-power or longer ISIs, but these modulatory effects were very small relative to inter-trial MEP variability. Our largely negative results are in agreement with previous offline TMS-EEG studies and point to a possible influence of ISI. Future research needs to clarify under which circumstances the responsiveness of human the M1-HAND to TMS depends on the synchronicity with mu-power and mu-phase. •Phase-triggered TMS at four phases of ongoing mu-oscillations is technically feasible in non-preselected young volunteers.•Targeting ongoing mu-activity did not reveal modulatory effects of mu-phase on corticospinal excitability.•Mixed-effects analysis reveal a weak but significant effect of pre-stimulus mu-power and ISI on corticospinal excitability.