LABORATORI NAZIONALI DEL GRAN SASSO
Transcranial magnetic stimulation (TMS) is a non-invasive technique that influences brain networks by applying a focused electric field (E-field) through a single coil placed over the scalp (Vlachos et al., 2022). The choice of the location and orientation of the E-field in TMS experiments is crucial as it induces cortex-specific effects and is supposed to modulate brain network communication (Marzetti et al., 2023). Recently, the development of multi-locus TMS (mTMS) has provided a tool to precisely modify the E-field without repositioning the coil manually (Nieminen et al., 2022). This allows one to study the effects of the stimulation on brain networks by systematically changing the parameters (Pieramico et al., 2023; Tervo et al., 2022). We investigated how the position and the orientation of the E-field during mTMS stimulation influence electroencephalographic (EEG) functional connectivity. Eight healthy participants underwent mTMS primarily targeting the left motor cortex (M1) and the left somatosensory cortex (S1) with a 5-coil mTMS system. The mTMS was used to modify the E-field by targeting 3 different positions on M1 and 3 different positions on S1 5 mm apart. EEG recordings were conducted with 64 electrodes to capture changes in functional connectivity modulated by the 5-coil mTMS pulses. Functional connectivity was estimated employing the imaginary part of the phase locking value (iPLV) (Palva & Palva, 2012); weighted degree centrality values were then computed from each connectivity matrix as the sum of its rows. This metric provides insights into the extent to which each EEG electrode is functionally connected to all others, i.e., its centrality. The results demonstrate that different mTMS stimulations modulate the degree centrality of different electrodes, i.e., different stimulations possibly modify the role of specific brain regions in the overall brain connectivity. Notably, the modulation of functional connectivity degree centrality varies not only across different positions over the primary motor and somatosensory cortices but also between these cortical regions. In conclusion, this study underscores the importance of considering both the intra- and inter-regional cortical target locations and individual variability when investigating the effects of mTMS on functional connectivity. Understanding these dynamics is crucial for accurately interpreting TMS-induced modulations of brain networks. ------ Giulia Pieramico Department of Engineering and Geology, University of Chieti-Pescara, Chieti, Italy Institute for Advanced Biomedical Technologies, University of Chieti-Pescara, Chieti, Italy Vittorio Pizzella Department of Neuroscience, Imaging and Clinical Sciences, University of Chieti-Pescara, Chieti, Italy Institute for Advanced Biomedical Technologies, University of Chieti-Pescara, Chieti, Italy

DATA: 06-03-2025