P092 Cortico-spinal and cortico-cortical excitability is influenced by the phase of oscillatory alpha activity at the time of the stimulus. Issue 3 (March 2017)

• Record Type: Journal Article
• Authors: Desideri, D.; Zrenner, C.; Belardinelli, P.; Ziemann, U.
• Is Part Of: Clinical neurophysiology. Volume 128:Issue 3(2017:Mar.)
• Page Start: e53
• Publication Date: 2017-03
• Subjects: Neurophysiology -- Periodicals; Electroencephalography -- Periodicals; Electromyography -- Periodicals; Neurology -- Periodicals; 612.8
• DOI: 10.1016/j.clinph.2016.10.217
• Languages: English
• ISSNs: 1388-2457

Abstract

Abstract : A somewhat surprising feature of the TMS evoked EEG and EMG potentials is their large variability. A number of factors are known to contribute to the variability of TMS responses but one factor about which tantalizingly little is known is the impact of instantaneous brain state at the time of stimulation. Here, we investigate the relationship between the phase of local mu-alpha oscillations at the time of stimulation with the magnitude of cortico-spinally evoked motor EMG potentials and the shape of the cortico-cortically evoked EEG potential. 12 healthy subjects were included the study and during a single session received TMS pulses over left motor cortex at an intensity to evoke EMG potentials at the right hand with 1 mV peak-to-peak amplitude. Phase triggers were generated based on the instantaneous phase of local sensorimotor rhythm using a Hjorth filter in the 5 EEG channels centered on electrode C3. The phase was estimated using a sliding window of data that was filtered, autoregressively forward predicted and hilbert transformed around the current time point in real-time using a custom closed-loop signal processing system based on Mathworks Simulink. The session consisted of a randomized sequence of 600 epochs in total, 300 triggered by the positive peak, and 300 triggered by the negative trough of the oscillations. Half of the trials were randomly not stimulated. Stimulated trials with pre-innervation in the EMG channel during the 500 ms preceding the stimulus were manually excluded. TMS evoked EEG potentials were analyzed by comparing the difference between stimulated and non-stimulated epochs after manually excluding trials with EEG artifacts, in order to subtract the oscillatory background activity. The magnitude of evoked motor potentials as measured by average peak-to-peak EMG potentials significantly differed by ca. 20% on average between the epochs evoked during the positive peak of ongoing alpha activity and the epochs evoked during the negative trough. At the level of the individual analysis, all of the 12 subjects showed a difference consistent with the group data (higher EMG amplitudes when stimulating in the negative trough of mu-alpha activity). The evoked EEG potentials showed a similar effect with the amplitude of the individual peaks higher when stimulating during the trough as compared to when stimulating during the peak.