Reconfigurations within resonating communities of brain regions following TMS reveal different scales of processing.

Javier O Garcia,Ramesh Srinivasan,Jean M Vettel,Danielle S Bassett,Arian Ashourvan,Steven M Thurman

doi:10.1162/netn_a_00139

Abstract

An overarching goal of neuroscience research is to understand how heterogeneous neuronal ensembles cohere into networks of coordinated activity to support cognition. To investigate how local activity harmonizes with global signals, we measured electroencephalography (EEG) while single pulses of transcranial magnetic stimulation (TMS) perturbed occipital and parietal cortices. We estimate the rapid network reconfigurations in dynamic network communities within specific frequency bands of the EEG, and characterize two distinct features of network reconfiguration, flexibility and allegiance, among spatially distributed neural sources following TMS. Using distance from the stimulation site to infer local and global effects, we find that alpha activity (8–12 Hz) reflects concurrent local and global effects on network dynamics. Pairwise allegiance of brain regions to communities on average increased near the stimulation site, whereas TMS-induced changes to flexibility were generally invariant to distance and stimulation site. In contrast, communities within the beta (13–20 Hz) band demonstrated a high level of spatial specificity, particularly within a cluster comprising paracentral areas. Together, these results suggest that focal magnetic neurostimulation to distinct cortical sites can help identify both local and global effects on brain network dynamics, and highlight fundamental differences in the manifestation of network reconfigurations within alpha and beta frequency bands.

Highlights

The brain is an intricate collection of heterogeneous areas (Alivisatos et al, 2012), and a central goal of neuroscientific research is to understand how the coordination of these different regions supports cognition (Azevedo et al, 2009; Bressler & Menon, 2010; Gollo, Roberts, & Cocchi, 2017)
We investigated network reconfigurations from resting-state EEG following single pulses of transcranial magnetic stimulation using a method from network science that reveals modular architecture in the brain (Bassett & Bullmore, 2006; Bullmore & Sporns, 2012; Ercsey-Ravasz et al, 2013)
transcranial magnetic stimulation (TMS) was delivered to two separate sites and we focused our analysis on two separate frequency bands

Summary

Introduction

The brain is an intricate collection of heterogeneous areas (Alivisatos et al, 2012), and a central goal of neuroscientific research is to understand how the coordination of these different regions supports cognition (Azevedo et al, 2009; Bressler & Menon, 2010; Gollo, Roberts, & Cocchi, 2017). One theoretical approach encapsulates the coordinated activity into a framework of scales, and research has examined how local regional activity harmonizes with global signals (Bressler & Kelso, 2001). Global activity arises from propagation delays in cortico-cortical fibers and reflects the dynamic interactions and synchronization among distal networks. This conceptual framework of local and global networks interacting in cognitive processes is critical to the interpretation of neurophysiological signals. How this activity coheres to manifest cognition is still an active area of study (Bressler & Kelso, 2001; Cocchi, Gollo, Zalesky, & Breakspear, 2017)

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Discussion

Conclusion