Platform Session – NIBS: Spatiotemporal dynamics of single and paired pulse TMS-EEG responses in healthy subjects

Abstract

Introduction Transcranial magnetic stimulation (TMS) is used for assessing cortical excitability in a variety of neurological disorders. Additional information from inhibitory and excitatory networks can be obtained with paired pulse stimulation. Combining TMS with electroencephalography (EEG) allows assessment of the spatiotemporal dynamics of neuronal responses in the stimulated brain. This study aims to evaluate the spread and distribution of single and paired pulse TMS-EEG responses in healthy controls. As cortical excitability is modified in various central nervous system disorders and for central acting drugs, these patterns can serve as a reference for future neurological and pharmacological studies. Methods Thirty healthy subjects (10 males, mean age 28.4 ± 8.2 years) underwent a single and paired pulse TMS-EEG session. Both motor cortices were stimulated with 50 single pulses and 50 paired pulses (intensity 120% of resting motor threshold) at interstimulus intervals (ISIs): 50, 100, 150, 200, 250 and 300 ms. The cluster based permutation test (FieldTrip; http://www.fieldtriptoolbox.org ) was used to analyze the spatiotemporal dynamics of the TMS-EEG response. Significant clusters were formed based on adjacent time bins and neighboring electrodes using 64-channel EEG data. Results Single pulse TMS-EEG responses showed the characteristic P30, N45, P55, N100 and P180 components at channel Cz. The P30 cluster was located centro-parietal in the ipsilateral hemisphere, the N45 centro-frontal contralateral, the P55 parieto-temporal ipsilateral, the N100 central contralateral and the P180 central contralateral and parieto-temporal ipsilateral. Both hemispheres showed a mirrored single pulse TMS-EEG response. For ISI 250 ms, the paired pulse TMS-EEG response also showed the characteristic components at Cz. However, the amplitudes were much smaller compared to single pulse stimulation. Furthermore, fewer, smaller and shorter-lasting significant clusters were found. For ISI 100 ms, no TMS-EEG components were visible at Cz and the response amplitude was much smaller compared to the single pulse response. Next, we will also compare single and paired pulse responses for the other ISIs (50, 150, 200 and 300 ms). Conclusion Stimulation of both hemispheres showed a mirrored single pulse TMS-EEG response. Paired pulse stimulation resulted in fewer, smaller and shorter-lasting clusters compared to single pulse TMS. In combination with a smaller response amplitude, this indicates inhibition of cortical excitability after a conditioning first stimulus. These spatiotemporal dynamics of the single and paired pulse TMS-EEG responses in healthy controls can serve as reference values for future TMS-EEG studies.