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

Chiara Mazzi; Sonia Mele; Chiara Bagattini; Javier Sanchez-Lopez; Silvia Savazzi

doi:10.3389/fnhum.2024.1362742

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

Front Hum Neurosci. 2024 Mar 7:18:1362742. doi: 10.3389/fnhum.2024.1362742. eCollection 2024.

Authors

Chiara Mazzi¹, Sonia Mele¹, Chiara Bagattini^{1

2}, Javier Sanchez-Lopez³, Silvia Savazzi¹

Affiliations

¹ Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
² Section of Neurosurgery, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
³ Escuela Nacional de Estudios Superiores Unidad Juriquilla, Universidad Nacional Autonoma de Mexico, Santiago de Querétaro, Mexico.

Abstract

Introduction: Low frequency (1 Hz) repetitive transcranial stimulation (rTMS) applied over right posterior parietal cortex (rPPC) has been shown to reduce cortical excitability both of the stimulated area and of the interconnected contralateral homologous areas. In the present study, we investigated the whole pattern of intra- and inter-hemispheric cortico-cortical connectivity changes induced by rTMS over rPPC.

Methods: To do so, 14 healthy participants underwent resting state EEG recording before and after 30 min of rTMS at 1 Hz or sham stimulation over the rPPC (electrode position P6). Real stimulation was applied at 90% of motor threshold. Coherence values were computed on the electrodes nearby the stimulated site (i.e., P4, P8, and CP6) considering all possible inter- and intra-hemispheric combinations for the following frequency bands: delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12Hz), low beta (12-20 Hz), high beta (20-30 Hz), and gamma (30-50 Hz).

Results and discussion: Results revealed a significant increase in coherence in delta, theta, alpha and beta frequency bands between rPPC and the contralateral homologous sites. Moreover, an increase in coherence in theta, alpha, beta and gamma frequency bands was found between rPPC and right frontal sites, reflecting the activation of the fronto-parietal network within the right hemisphere. Summarizing, subthreshold rTMS over rPPC revealed cortico-cortical inter- and intra-hemispheric connectivity as measured by the increase in coherence among these areas. Moreover, the present results further confirm previous evidence indicating that the increase of coherence values is related to intra- and inter-hemispheric inhibitory effects of rTMS. These results can have implications for devising evidence-based rehabilitation protocols after stroke.

Keywords: EEG oscillatory dynamics; functional connectivity; inter-hemispheric coherence; rTMS; resting state.

Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. Work supported by #NEXTGENERATIONEU (NGEU) and funded by the Ministry of University and Research (MUR), National Recovery and Resilience Plan (NRRP), project MNESYS (PE0000006)—“A Multiscale integrated approach to the study of the nervous system in health and disease” (DN. 1553 11.10.2022); MIUR PRIN 2017, “From brain dynamics to restoration of visual awareness after damage to the visual cortex.” grant no. 2017TBA4KS_002; Fondazione Cassa di Risparmio di Verona, Vicenza, Belluno e Ancona “Ricerca scientifica d'eccellenza 2018”, “Emergence of Consciousness: From neural dynamics to complex conscious behavior” grant no. 2018.0861; and CM was supported by MIUR D.M. 737/2021—“Neural correlates of perceptual awareness: from neural architecture to the preservation of conscious vision in brain tumor patients”.