PhD Scientific Days 2021

NE_II_L: Neurosciences II. Lectures

Network Path Convergence Shapes Low-Level Processing in the Visual Cortex

Text of the abstract

Introduction
Cognition emerges by counterstream feedforward and feedback interactions in the large-scale, hierarchical network of the cerebral cortex. Although cortical dynamics are rooted in the anatomical network, the relationship of structure and function is far from clear. The counterstream, as a topological feature of the network, is captured by the convergence and divergence of paths through directed links. So defined, the convergence degree (CD) reveals the reciprocal nature of forward and backward connections, and also hierarchically relevant integrative properties of areas.

Aims
To understand how topology shapes large-scale cortical functioning, and what is the relationship between anatomical (determined by the laminar distribution of connections), topological (defined by CD) and functional (determined by causal coupling) hierarchies.

Methods
We used CD to characterize the topology of signal flow properties and implemented an oscillating neural mass model of hierarchical network dynamics. Functional connectivity was computed by spectral Granger causality. Relationships of topology and dynamics were studied via correlations.

Results
Similar to anatomical hierarchy, CD-based topological hierarchy showed high correlation with causal coupling in feedforward gamma and feedback alpha-beta band synchronizations in a subnetwork including low-level visual cortical areas. In contrast, causal coupling did not correlate with edge betweenness, another measure of the importance of network links. Considering the entire network, the CD-based hierarchy correlated well with both the anatomical and functional hierarchy for low-level areas that are hierarchically far apart. Conversely, in a large part of the anatomical network where hierarchical distances are small, correlations were not significant.

Conclusion
These findings indicate that at lower levels of cortical hierarchy interareal connectivity closely shapes large-scale oscillatory dynamics. However, at higher levels hierarchy is not strictly determined, allowing for a flexibility in hierarchical interactions needed to cope with varying demands.

Funding
This work was supported by the Hungarian Scientific Research Fund (OTKA); Grant Numbers: NN118902 and K135837, the Wigner RCP and the Eötvös Loránd Research Network (ELKH).

University and Doctoral School

Semmelweis University, János Szentágothai Doctoral School of Neurosciences