Year: 2015
Type: dissertation
Abstract: The adult human brain comprises an estimated number of 80-100 billion neurons. These \nneurons do not operate independently, but are interconnected to each other through circa \n100-500 trillion neuronal connections, together forming a network of incredible \ncomplexity. Although this vast system of neurons and neuronal connections – known as \nthe connectome – can (currently) not be mapped in full detail, the organization of the \nneural infrastructure which enables us to move, sense, memorize, and think does not have \nto remain elusive. On a larger and more comprehensible scale, neurons are organized into \nanatomically and functionally distinguishable brain regions and their neuronal \nconnections form large-scale white matter fibers. Especially during the last two decades, \nmapping this macroscale connectome of brain regions and white matter fibers has become \nincreasingly feasible and studies have gradually started to unravel its intriguing network \narchitecture. In this thesis, we continue along this path to elucidate the macroscale \nnetwork organization of our brain a little further. To do so, we adopt a somewhat unusual \nperspective on brain networks, shifting the conventional focus on brain regions to a focus \non the connectome's connections. We first consider the reliability of reconstructed white \nmatter fibers and introduce a model which helps to reduce the number of false positive and \nfalse negative connections in macroscale connectome reconstructions. Subdividing the \nconnections of the connectome into different categories, we then demonstrate that \nconnections between highly connected and highly central hub regions are frequently \nbidirectional and intermodular (i.e., positioned between different subsystems) and tend to \nbe longer and stronger than other types of connections; properties which make them ideal \ncandidates to form the connections of a “global workspace” in the brain. In support of this \nhypothesis, we propose a framework to obtain a more direct assessment of the network \nrole of connections and show that hub-to-hub connections play a pronounced role in the \ncommunication and integration between different functional subsystems. We further show \nthat the white matter fibers of our brain are intrinsically organized into so-called link \ncommunities and that hub regions form “hot spots” were connections from a variety of link \ncommunities come together. In all, these findings corroborate the idea that hubs and their \nconnections may form a central infrastructure for multimodal and integrative processes in \nthe brain. Moreover, the identified link communities and proposed connection measures \nmay provide interesting targets and tools for studies on the diseased brain, potentially \nallowing better localization and characterization of connectome differences between \npatients and controls.
Author: Marcel A. de Reus
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
Awards: G8299918676, G9000089182
OpenAlex ID: W1921365454