Structural Brain Connectivity Constrains within-a-Day Variability of Direct Functional Connectivity.

Area of Science:

• Neuroscience
• Brain Connectivity
• Network Science

Background:

• Structural white matter connectivity is known to influence functional connectivity (FC) in brain networks.
• However, how structural connectivity constrains the *variability* of FC over time remains largely unexplored.
• Understanding this dynamic constraint is crucial for a comprehensive model of brain function.

Purpose of the Study:

• To investigate how structural connectivity constrains the within-day variability of resting-state functional connectivity (rsFC).
• To examine the influence of different structural connectivity properties (e.g., streamline counts, lengths, edge types) on FC variability.
• To assess whether structural constraints differ across various types of functional connectivity measures.

Main Methods:

• Acquired resting-state functional magnetic resonance imaging (rs-fMRI) data every 3 hours over 24 hours from 12 participants.
• Estimated three types of FC (Pearson correlation, partial correlation, and their difference) and structural connectivity (SC) using diffusion tensor imaging (DTI) fiber tractography.
• Evaluated the relationship between SC properties (e.g., intra-/inter-hemispheric edges, rich club organization) and FC variability.

Main Results:

• Structural connectivity significantly constrained the variability of direct functional connectivity (partial correlation) more than other FC measures.
• These structural constraints were dependent on edge types, being stronger for intra-hemispheric and heterologous inter-hemispheric connections than homologous ones.
• While individual connections varied, multivariate patterns of direct FC, especially within rich club regions, exhibited low temporal variability.

Conclusions:

• Structural connectivity not only dictates the average strength but also the temporal variability of functional connectivity.
• The findings highlight the critical role of specific structural connections, particularly within rich club architecture, in stabilizing functional brain dynamics.
• This provides a more nuanced understanding of the structure-function relationship in the human brain over short timescales.