Graph Analysis of TMS–EEG Connectivity Reveals Hemispheric Differences following Occipital Stimulation

Abstract

(1) Background: Transcranial magnetic stimulation combined with electroencephalography (TMS–EEG) provides a unique opportunity to investigate brain connectivity. However, possible hemispheric asymmetries in signal propagation dynamics following occipital TMS have not been investigated. (2) Methods: Eighteen healthy participants underwent occipital single-pulse TMS at two different EEG sites, corresponding to early visual areas. We used a state-of-the-art Bayesian estimation approach to accurately estimate TMS-evoked potentials (TEPs) from EEG data, which has not been previously used in this context. To capture the rapid dynamics of information flow patterns, we implemented a self-tuning optimized Kalman (STOK) filter in conjunction with the information partial directed coherence (iPDC) measure, enabling us to derive time-varying connectivity matrices. Subsequently, graph analysis was conducted to assess key network properties, providing insight into the overall network organization of the brain network. (3) Results: Our findings revealed distinct lateralized effects on effective brain connectivity and graph networks after TMS stimulation, with left stimulation facilitating enhanced communication between contralateral frontal regions and right stimulation promoting increased intra-hemispheric ipsilateral connectivity, as evidenced by statistical test (p < 0.001). (4) Conclusions: The identified hemispheric differences in terms of connectivity provide novel insights into brain networks involved in visual information processing, revealing the hemispheric specificity of neural responses to occipital stimulation.

Mapping the routes of perception: Hemispheric asymmetries in signal propagation dynamics

“…In a recent paper, Siviero et al (2023) analyzed the same data sets through the use of effective connectivity and graph networks, confirming the reliability of our conclusions. Effective connectivity is characterized as the influence that one neural system has over another via causal or non-causal effects (Friston, 2011): it allows to understand how the different information flows are integrated within the brain network, clarifying specific pathways of neural activity.…”

Coherent activity within and between hemispheres: cortico-cortical connectivity revealed by rTMS of the right posterior parietal cortex

“…Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive method to temporarily modulate neural activity (Silvanto and Muggleton, 2008 ; Miniussi et al, 2013 ) with long-lasting changes of cortical excitability (Robertson et al, 2003 ). Importantly, rTMS not only acts locally on interneural circuits underneath the coil but its effects also spread to functionally connected brain regions along cortico-cortical connections (Bortoletto et al, 2015 ; Siviero et al, 2023 ). When TMS is coupled with EEG, it is possible to map the network of cortical areas engaged in a specific cognitive function and give information on the functional coupling among brain areas with a very high temporal resolution (Ilmoniemi et al, 1997 ; Miniussi and Thut, 2010 ) thus providing information on the causal role of TMS-induced cortical changes on distant, but functionally interconnected, areas.…”