Similarity between structural and proxy estimates of brain connectivity.

Area of Science:

• Neuroscience
• Brain Imaging
• Connectomics

Background:

• Functional magnetic resonance imaging (fMRI) and diffusion-weighted imaging (DWI) are key for mapping the macroscale brain connectome.
• The relationship between structural connectivity (SC) and functional connectivity (FC) is partially understood, but their spatial overlap remains unclear.
• The relationship of SC with connectivity estimates derived from inter-subject covariance of F18-fluorodeoxyglucose uptake (FDG_cov) and grey matter volume (GMV_cov) is even less clear.

Purpose of the Study:

• To investigate the extent to which structural connectivity (SC) underlies three proxy estimates of brain connectivity: functional connectivity (FC), FDG_cov, and GMV_cov.

Main Methods:

• Simultaneous Positron Emission Tomography (PET)/Magnetic Resonance (MR) imaging was conducted in 56 healthy middle-aged individuals.
• Similarity between the four connectivity networks (SC, FC, FDG_cov, GMV_cov) was assessed using Spearman correlation.
• Spatial overlap was quantified using the convergence ratio (CR).

Main Results:

• Spearman correlation coefficients revealed moderate similarity between SC and FC (0.27), and SC and FDG_cov (0.40), but weak similarity between SC and GMV_cov (0.15).
• Mean convergence ratios (CR) indicated substantial spatial overlap: 51% for SC-FC, 48% for SC-FDG_cov, and 37% for SC-GMV_cov.
• Results were reproducible and robust across different image processing steps.

Conclusions:

• Structural connectivity (SC) shows relevant similarity with functional connectivity (FC) and F18-fluorodeoxyglucose uptake covariance (FDG_cov).
• Grey matter volume covariance (GMV_cov) demonstrated the weakest similarity to SC.
• FDG_cov is supported as a valid estimate of functional brain connectivity, comparable in its underlying white matter structure to FC.