Time - frequency analysis of short - lasting modulation of EEG induced by intracortical 1 and transcallosal paired TMS over motor areas

27 Dynamic changes in spontaneous electroencephalogram (EEG) rhythms can be seen to occur 28 with a high rate of variability. An innovative method to study brain function is by triggering 29 oscillatory brain activity with transcranial magnetic stimulation (TMS). EEG-TMS 30 coregistration was performed on five healthy subjects during a one-day experimental session 31 that involved four steps: baseline acquisition; unconditioned single-pulse TMS; intracortical 32 inhibition (ICI, 3 ms) paired-pulse TMS; and transcallosal stimulation over the left and the 33 right primary motor cortex (M1). A time-frequency analysis based on the wavelet method was 34 used to characterize rapid modifications of oscillatory EEG rhythms induced by TMS. Single, 35 paired, and transcallosal TMS applied on the sensorimotor areas induced rapid 36 desynchronization over the frontal and central-parietal electrodes mainly in the alpha and beta 37 bands, followed by a rebound of synchronization, and rapid synchronization of delta and theta 38 activity. Wavelet analysis after a perturbation approach is a novel way to investigate 39 modulation of oscillatory brain activity. The main findings are consistent with the concept 40 that the human motor system may be based on network-like oscillatory cortical activity and 41 might be modulated by single, paired and transcallosal magnetic pulses applied to M1, 42 suggesting a phenomenon of fast brain activity resetting and triggering of slow activity. 43 44