Abstract
While significant progress has been achieved in studying resting-state functional networks in a healthy human brain and in a wide range of clinical conditions, many questions related to their relationship to the brain’s cellular constituents remain. Here, we use quantitative Gradient-Recalled Echo (qGRE) MRI for mapping the human brain cellular composition and BOLD (blood–oxygen level-dependent) MRI to explore how the brain cellular constituents relate to resting-state functional networks. Results show that the BOLD signal-defined synchrony of connections between cellular circuits in network-defined individual functional units is mainly associated with the regional neuronal density, while the between-functional units’ connectivity strength is also influenced by the glia and synaptic components of brain tissue cellular constituents. These mechanisms lead to a rather broad distribution of resting-state functional network properties. Visual networks with the highest neuronal density (but lowest density of glial cells and synapses) exhibit the strongest coherence of the BOLD signal as well as the strongest intra-network connectivity. The Default Mode Network (DMN) is positioned near the opposite part of the spectrum with relatively low coherence of the BOLD signal but with a remarkably balanced cellular contents, enabling DMN to have a prominent role in the overall organization of the brain and hierarchy of functional networks.
Highlights
Resting-state functional brain connectivity has become an established area of research in the arena of cognitive neuroscience and its related applications
For resting-state functional MRI (rs-fMRI), we provide data analysis based on a structure of 300 parcels combined in 17 resting-state networks developed by Yeo et al [7,30]
We provide a data analysis based on a structure of 300 gradient-weighted Markov Random Field (gwMRF) ROIs combined in 17 resting-state networks developed by Yeo et al [7,30]
Summary
Resting-state functional brain connectivity has become an established area of research in the arena of cognitive neuroscience and its related applications. Functional connectivity refers to the statistical correlation between temporally coherent low-frequency spontaneous fluctuations of the resting-state functional MRI (rs-fMRI) signal in different brain regions [1] and provides insight into the large-scale brain circuit organization [2,3]. The rs-fMRI signal is acquired with MRI sequences sensitive to the Blood–Oxygen Level-Dependent (BOLD) effect [4] and identifies consistent resting-state networks [5,6,7] that play important roles in both normal brain function and various neurological conditions, such as, for example, normal aging [8] and Alzheimer disease [9]. An important question in understanding the physiological basis of resting-state functional connectivity is its relationship to brain structural connectivity and brain cellular composition. The direct structural connectivity through WM is not the sole mechanism underlying functional connectivity [14,15]
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