The registration of the electroencephalography during the application of transcranial magnetic stimulation, i.e., the TMS-EEG coregistration technique, has been first proposed in the late nineties as a means to measure cortical excitability and cortico-cortical connectivity. Despite its ongoing methodological challenges, this technique yields unique insights into brain activity, and its application in cognitive neuroscience is expanding. Here, I will present how TMS-EEG has advanced since its early stages, and how it can be employed to understand the human brain in physiological and pathological conditions. I will show evidence that TMS-evoked potentials reflect the activation of cortico-cortical connections, and that they can reveal network activity modulation during task execution. In applied research, they have been exploited to develop diagnostic and progression biomarkers of network diseases, as Alzheimer’s dementia. Finally, I will highlight the collaborative efforts of TMS-EEG experts to further advance the methodology of this technique and foster more reproducible results.
Current advances in EEG systems allow to extract cortical responses evoked by TMS pulses, i.e., TMS- evoked potentials, very early after the TMS pulse. Here, I will show evidence that these responses contain unique information on the network in which the stimulated area is embedded. Several studies suggest that TEPs represent secondary responses of distant areas connected to the initial target. Features of very early-latency TEPs are associated with structural and functional connectivity measures of specific white matter tracks and are modulated during task execution. Moreover, given the high temporal and spatial resolution of TMS, it is possible to exploit TEPs to track changes in cortico-cortical connectivity during task execution and gain a better understanding of the physiological mechanisms that subtend behaviour.
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