Concordance Among Indices of Intrinsic Brain Function: Inter-Individual Variation and Temporal Dynamics Perspectives

Various resting-state fMRI (R-fMRI) measures have been developed to characterize intrinsic brain activity, while questions remain regarding the common and unique aspects these indices capture. The present work provided a comprehensive examination of inter-individual variation and intra-individual temporal variation for commonly used measures. Regardless of whether examining intra-individual or inter-individual variation, we found that these definitionally distinct R-fMRI indices tend to exhibit a relatively high degree of covariation. When taken as a measure of intrinsic brain function, inter-individual differences in concordance for R-fMRI indices appeared to be stable, and negatively related to age. To understand the functional significance of concordance, we noted that higher concordance was generally associated with higher strengths of R-fMRI indices, either at inter-individual (i.e., high vs. low concordance participants) or intra-individual (i.e., high vs. low concordance states identified via temporal dynamic analyses) levels. Finally, temporal dynamics analyses revealed that high concordance states are characterized by increased withinand between-network functional connectivity, suggesting more general variations in network integration and segregation. The current study draws attention to questions regarding selecting an R-fMRI index for usage in a given study, as well as comparing findings across studies that examine inter-individual or group differences using different indices.