Mapping how local perturbations influence systems-level brain dynamics

Abstract

The human brain exhibits a relatively stable spatiotemporal organization that supports brain function and can be manipulated via local brain stimulation. Such perturbations to local cortical dynamics are globally integrated by distinct neural systems. However, it remains unclear how and why local changes in neural activity affect large-scale system dynamics. Here, we briefly review empirical and computational studies addressing how localized perturbations affect brain activity. We then systematically analyze a model of large-scale brain dynamics, assessing how localized changes in brain activity at the different sites affect whole-brain dynamics. We find that local stimulation induces changes in brain activity that can be summarized by relatively smooth tuning curves, which relate a region's effectiveness as a stimulation site to its position within the cortical hierarchy. Our results also support the notion that brain hubs, operating in a slower regime, are more resilient to focal perturbations and critically contribute to maintain stability in global brain dynamics. In contrast, perturbations of peripheral regions, characterized by faster activity, have greater impact on functional connectivity. As a parallel with this region-level result, we also find that peripheral systems such as the visual and sensorimotor networks were more affected by local perturbations than high-level systems such as the cingulo-opercular network. Our results highlight the importance of a periphery-tocore hierarchy to determine the effect of local stimulation on the brain network. We also provide novel resources to orient empirical work aiming at manipulating functional connectivity using noninvasive brain stimulation.3

Inferring neural signalling directionality from undirected structural connectomes

“…Several studies of axonal tract-tracing and non-human connectomes [37,50,52], macroscale gradients of cortical organization [38,40,53], and computational models of neuronal dynamics [29,[54][55][56][57] converge to a common conceptualization of cortical hierarchies. The bottom of the hierarchy tends to comprise high-frequency, low-degree, unimodal, sensory and motor areas that constitute the main inputs of perceptual information to the brain.…”

“…The concept of send-receive communication asymmetry provides opportunities to infer putative directions of neural information flow in the human connectome using traditional in vivo diffusion MRI coupled with established fiber tracking methods, which inherently cannot resolve the directionality of white matter fibers. Therefore, investigating decentralized network communication mea-sures may help bridge the gap between our symmetric understanding of human connectome structure and the ample evidence for its asymmetric functional dynamics [27][28][29].…”

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

“…The brain is an intricate collection of heterogeneous areas (Alivisatos et al, 2012), and a central goal 41 of neuroscientific research is to understand how the coordination of these different regions support 42 cognition (Azevedo et al, 2009;Bressler and Menon, 2010;Gollo et al, 2017). One theoretical 43 approach encapsulates the coordinated activity into a framework of scales, and research has 44 examined how local regional activity harmonizes with global signals (Bressler and Kelso, 2001).…”

Introducing axonal myelination in connectomics: A preliminary analysis of g-ratio distribution in healthy subjects

“…A further perspective related to plasticity is non-invasive brain stimulation: recent works have used network modelling to investigate the mechanisms of transcranial magnetic stimulation (TMS) given the structural connectivity and the stimulation site (Cocchi et al, 2016;Gollo et al, 2017). This approach has provided interesting insights in how brain dynamics respond to focal perturbations that could be extended integrating the g-ratio.…”