TMS and TMS-EEG techniques in the study of the excitability, connectivity, and plasticity of the human motor cortex

Increasing evidence supports the notion that brain plasticity involves distinct functional and structural components, each entailing a number of cellular mechanisms operating at different time scales, synaptic loci, and developmental phases within an extremely complex framework. However, the exact relationship between functional and structural components of brain plasticity/connectivity phenomena is still unclear and its explanation is a major challenge within modern neuroscience. Transcranial magnetic stimulation (TMS), with or without electroencephalography (EEG), is a sensitive and objective measure of the effect of different kinds of noninvasive manipulation of the brain's activity, particularly of the motor cortex. Moreover, the key feature of TMS and TMS-EEG coregistration is their crucial role in tracking temporal dynamics and inner hierarchies of brain functional and effective connectivities, possibly clarifying some essential issues underlying brain plasticity. All together, the findings presented here are significant for the adoption of the TMS and TMS-EEG coregistration techniques as a tool for basic neurophysiologic research and, in the future, even for clinical diagnostics purposes.