Abstract
Functional Connectivity (FC) in resting-state or task conditions is not frozen but inherently dynamic. Yet, there is no consensus on whether fluctuations in FC resemble isolated transitions between discrete FC states rather than continuous changes. This quarrel hampered advancing the study of dynamic FC. This is unfortunate as the structure of fluctuations in FC can provide crucial information about developmental changes, aging, or progression of pathologies. We merge the two perspectives and consider dynamic FC as continuous network reconfiguration, including a stochastic exploration of the space of possible steady FC states. The statistical properties of this random walk deviate both from an “order-driven” dynamics, in which the mean FC is preserved, and from a “randomness-driven” scenario, in which fluctuations of FC remain uncorrelated over time. Instead, dynamic FC turns out to have a complex structure endowed with long-range sequential correlations giving rise to transient slowing and acceleration epochs in the continuous flow of reconfiguration. When applying our analysis to an fMRI dataset in healthy elderly, we find that the dynamic FC tends to slow down, becomes less complex and more random with increasing age. All these effects are strongly associated with age-related changes in cognitive performance.
Highlights
Dynamic Functional Connectivity (dFC) at rest and during cognitive task performs a “complex” (anomalous) random walk.
Speed of dFC slows down with aging.
Resting dFC replaces complexity by randomness with aging.
Task performance correlates with the speed and complexity of dFC.
Footnotes
↵+ Shared last authorship
Other e-mail addresses: Thomas Boudou, thomas.boudou{at}ensta-paristech.fr, Enrique C. A. Hansen, hansen{at}biologie.ens.fr, Diego Lombardo, diego.lombardo{at}univ-amu.fr, Sabrina Chettouf, sabrina.chettouf{at}charite.de, Andreas Daffertshofer, a.daffertshofer{at}vu.nl, A. Randal McIntosh, rmcintosh{at}research.baycrest.org, Joelle Zimmermann, jzimmermann{at}research.baycrest.org, Petra Ritter, petra.ritter{at}charite.de, Viktor Jirsa, viktor.jirsa{at}univ-amu.fr
This version replaces a previous preprint submitted in 2017. All analyses had to be repeated following discovery of problems in preprocessing. All results were confirmed, but, meanwhile, our understanding of the methods had considerably progressed, leading to major changes in our presentation (also taking in account new analyses). This manuscript is thus the first of a fully new diptych containing a comprehensive presentation of our current vision of dFC as a random walk in FC space with complex spatiotemporal structure.
Abbreviations
- rs
- resting-state
- RSN
- resting-state network
- fMRI
- functional magnetic resonance imaging
- BOLD
- blood oxygen level dependent
- SC
- structural connectivity
- FC
- functional connectivity
- dFC
- dynamic functional connectivity
- DFA
- detrended fluctuation analysis
- MoCA
- Montreal Cognitive Assessment
- SO
- spectral overlap