Poster F76, Tuesday, March 27, 8:00-10:00 am, Exhibit Hall C
Alpha phase modulates the amplitude and variance of suprathreshold TMS-induced motor evoked potentials
Lukas Schilberg1,2, Sanne ten Oever1,2, Teresa Schuhmann1,2, Alexander T. Sack1,2; 1Maastricht University, 2Maastricht Brain Imaging Center
Transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) are frequently examined in research and clinical settings as measures of corticospinal excitability (CSE). Their evaluation promises valuable information about fundamental brain related mechanisms and is applied for clinical monitoring of treatments and surgery procedures. Although reliability of MEPs is of uttermost importance, concerns about high intra-individual variability have rendered MEPs as potentially unreliable measures. One possible cause for high variability of MEPs could be neuronal oscillatory activity at the time and location of TMS administration, which reflects fluctuations of membrane potentials that systematically increase and decrease the excitability of neuronal networks. Here, we investigate the dependence of MEP amplitude and variance on intrinsic oscillation power and phase by combining suprathreshold single pulse TMS (at 120% of resting motor threshold) with electroencephalography (EEG). We show that MEP amplitude is correlated to the phase of the ongoing alpha oscillations (8.9 to 12.4Hz) at TMS site. Moreover, the phase of the 50% highest MEP amplitudes is consistent across participants (centered around -0.5pi). Finally, we show that the magnitudes of MEP amplitude and variability differ between phases of the alpha oscillation. In conclusion, MEP amplitude and variance are dependent on the phase of alpha at the time and location of TMS. Locking TMS to a certain alpha phase could lead to lower variability and increased reliability of MEPs. Our findings are important for the development of essentially reliable measures of CSE. In addition, they can help to increase the efficacy of TMS applications in general.
Topic Area: METHODS: Electrophysiology