Abstract
Spontaneous brain activity, typically investigated using resting-state fMRI (rsfMRI), provides a measure of inter-areal resting-state functional connectivity (RSFC). Although it has been established that RSFC is non-stationary, previous dynamic rsfMRI studies mainly focused on revealing the spatial characteristics of dynamic RSFC patterns, but the temporal relationship between these RSFC patterns remains elusive. Here we investigated the temporal organization of characteristic RSFC patterns in awake rats and humans. We found that transitions between RSFC patterns were not random but followed specific sequential orders. The organization of RSFC pattern transitions was further analyzed using graph theory, and pivotal RSFC patterns in transitions were identified. This study has demonstrated that spontaneous brain activity is not only nonrandom spatially, but also nonrandom temporally, and this feature is well conserved between rodents and humans. These results offer new insights into understanding the spatiotemporal dynamics of spontaneous activity in the mammalian brain.
Highlights
Multiple lines of evidence indicate that spontaneous brain activity plays an essential role in brain function (Raichle ME and MA Mintun 2006; Zhang D and ME Raichle 2010)
Anatomical MRI images were acquired using a T1-weighted rapid imaging with refocused echoes (RARE) sequence with the following parameters: repetition time (TR) = 1500 ms; echo time (TE) = 8 ms; matrix size = 256 × 256; field of view (FOV) = 3.2 × 3.2 cm2; slice number = 20; slice thickness = 1 mm; RARE factor = 8. resting-state functional magnetic resonance imaging (rsfMRI) images were acquired using a T2*-weighted gradient-echo echo planar imaging (EPI) sequence with the following parameters: TR = 1000 ms; TE =15 ms; matrix size = 64 × 64; FOV = 3.2 × 3.2 cm2; slice number = 20; slice thickness= 1 mm. 600 EPI volumes were acquired for each run, and two to four runs were acquired for each animal
In this study, we investigated the temporal transitions between spontaneous brain activity patterns in awake rats and humans
Summary
Multiple lines of evidence indicate that spontaneous brain activity plays an essential role in brain function (Raichle ME and MA Mintun 2006; Zhang D and ME Raichle 2010). Using spontaneously fluctuating blood-oxygenation-level dependent (BOLD) signal measured by rsfMRI, resting-state functional connectivity (RSFC) between brain regions can be gauged by statistical interdependence of their rsfMRI signals over the period of data acquisition (Fox MD and ME Raichle 2007). Meaningful temporal variability of RSFC at shorter time scales within rsfMRI scans has been discovered (Chang C and GH Glover 2010) This initial research and its follow-up studies revealed dynamic properties of RSFC, indicating that the stationarity assumption of RSFC would be overly simplistic for understanding spontaneous brain activity (Hutchison RM, T Womelsdorf, EA Allen, et al 2013; Preti MG et al 2016). The neurophysiologic relevance of dynamic RSFC has been validated in multiple studies using simultaneous electrophysiology and rsfMRI acquisitions (Tagliazucchi E et al 2012; Chang C et al 2013; Keilholz SD 2014)
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