Network Effects of Left M1 rTMS: A TMS-EEG Study (CORTEX-4)

This study aims to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) applied to the left primary motor cortex (left M1) on cortical reactivity and brain connectivity in healthy volunteers using combined transcranial magnetic stimulation and electroencephalography (TMS-EEG).

Brain function depends on the dynamic interaction of distributed neuronal networks that allow efficient communication between cortical regions. Alterations in these connectivity patterns have been associated with several neurological and neuropsychiatric disorders, including chronic pain, depression, and motor dysfunction. Non-invasive neuromodulation techniques such as repetitive transcranial magnetic stimulation (rTMS) can influence cortical excitability and modulate activity within interconnected brain networks.

rTMS is a safe and non-invasive technique that uses rapidly changing magnetic fields to induce electrical currents in targeted cortical areas. Depending on the stimulation parameters, rTMS may facilitate or inhibit neuronal activity locally and across connected brain regions. Despite its increasing clinical use, the neurophysiological mechanisms through which rTMS modifies large-scale brain connectivity remain incompletely understood.

In this study, healthy volunteers will undergo TMS-EEG recordings before and after one session of active rTMS delivered over the left primary motor cortex. TMS pulses will be applied to four cortical targets - left primary motor cortex (M1), right primary motor cortex (M1), left premotor cortex, and right occipital cortex - in order to assess local cortical reactivity and the propagation of neural activity across distinct brain regions. TMS-evoked potentials (TEPs) recorded with EEG will serve as electrophysiological markers of cortical excitability and connectivity.

The study seeks to characterise how stimulation of the left M1 modulates both local and distributed cortical responses. Specifically, it is hypothesised that one session of active rTMS over the left M1 will induce measurable changes in TEPs and alter connectivity patterns across motor and non-motor cortical networks. These findings may contribute to a better understanding of the neurophysiological mechanisms underlying rTMS-induced plasticity and network modulation.