Similarity between structural and proxy estimates of brain connectivity
Aldana Lizarraga, Isabelle Ripp, Arianna Sala, Kuangyu Shi, Marco Düring, Kathrin Koch, Igor Yakushev
Abstract
Functional magnetic resonance and diffusion weighted imaging have so far made a major contribution to delineation of the brain connectome at the macroscale. While functional connectivity (FC) was shown to be related to structural connectivity (SC) to a certain degree, their spatial overlap is unknown. Even less clear are relations of SC with estimates of connectivity from inter-subject covariance of regional F18-fluorodeoxyglucose uptake (FDG cov ) and grey matter volume (GMV cov ). Here, we asked to what extent SC underlies three proxy estimates of brain connectivity: FC, FDG cov and GMV cov . Simultaneous PET/MR acquisitions were performed in 56 healthy middle-aged individuals. Similarity between four networks was assessed using Spearman correlation and convergence ratio (CR), a measure of spatial overlap. Spearman correlation coefficient was 0.27 for SC-FC, 0.40 for SC-FDG cov , and 0.15 for SC-GMV cov . Mean CRs were 51% for SC-FC, 48% for SC-FDG cov , and 37% for SC-GMV cov . These results proved to be reproducible and robust against image processing steps. In sum, we found a relevant similarity of SC with FC and FDG cov , while GMV cov consistently showed the weakest similarity. These findings indicate that white matter tracts underlie FDG cov to a similar degree as FC, supporting FDG cov as estimate of functional brain connectivity.