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

Kristoffer Hougaard Madsen*, Anke Ninija Karabanov, Lærke Gebser Krohne, Mads Gylling Safeldt, Leo Tomasevic, Hartwig Roman Siebner

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Background: 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.
Objectives: 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.
Methods: TMS was given at 0, 90, 180, and 270 of the mu-phase. Based on the absence of effects of muphase 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.
Results: Mixed model analysis revealed a significant effect of mu-power and ISI, but no effect of muphase 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. Conclusion: 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 muphase.
Original languageEnglish
JournalBrain Stimulation
Issue number5
Pages (from-to)1261-1270
Number of pages10
Publication statusPublished - 2019


  • Electroencephalography
  • EEG-Triggered phase targeting
  • Mu rhythm
  • Pericentral oscillation
  • Temporal and spatial neuronavigation
  • Transcranial magnetic stimulation


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