TMS measures explored by EEG recordings

This chapter describes the use of electroencephalography (EEG) to measure neuronal activity evoked by transcranial magnetic stimulation (TMS). We discuss the major research and clinical applications of TMS-EEG and review synthetic measures designed to assess the functional status of cortical networks, such as neuronal excitability and effective connectivity. We first highlight that brain reactivity to TMS crucially depends on the anatomical and functional characteristics of the cortical region being stimulated. These findings suggest that the responses to stimulation of the primary motor cortex should be considered a special rather than a representative case of the brain's reaction to TMS. Next, we describe TMS-EEG-based measures of (i) cortical reactivity in the time and frequency domains, (ii) excitation and inhibition provided by paired-pulse paradigms, and (iii) neuroplasticity induced by non-invasive neuromodulatory interventions. Finally, we discuss the methodological challenges related to concurrent TMS-EEG and review methods for minimizing/suppressing artifacts that may contaminate brain signals. We conclude that TMS-EEG has great potential for becoming an effective research and clinical tool, provided that: 1) data quality is monitored in real time; 2) effective and sound artifact-removal methods are developed and implemented; and 3) sufficient control studies are performed to assess the impact of TMS on the cortex.