  This paper studies the link between resting-state functional connectivity
(FC), measured by the correlations of the fMRI BOLD time courses, and
structural connectivity (SC), estimated through fiber tractography. Instead of
a static analysis based on the correlation between SC and the FC averaged over
the entire fMRI time series, we propose a dynamic analysis, based on the time
evolution of the correlation between SC and a suitably windowed FC. Assessing
the statistical significance of the time series against random phase
permutations, our data show a pronounced peak of significance for time window
widths around 20-30 TR (40-60 sec). Using the appropriate window width, we show
that FC patterns oscillate between phases of high modularity, primarily shaped
by anatomy, and phases of low modularity, primarily shaped by inter-network
connectivity. Building upon recent results in dynamic FC, this emphasizes the
potential role of SC as a transitory architecture between different highly
connected resting state FC patterns. Finally, we show that networks implied in
consciousness-related processes, such as the default mode network (DMN),
contribute more to these brain-level fluctuations compared to other networks,
such as the motor or somatosensory networks. This suggests that the
fluctuations between FC and SC are capturing mind-wandering effects.
