title: Interplay between functional connectivity and scale-free dynamics in intrinsic fMRI networks.
abstract: Studies employing functional connectivity-type analyses have established that spontaneous fluctuations in functional magnetic resonance imaging (fMRI) signals are organized within large-scale brain networks. Meanwhile, fMRI signals have been shown to exhibit 1/f-type power spectra - a hallmark of scale-free dynamics. We studied the interplay between functional connectivity and scale-free dynamics in fMRI signals, utilizing the fractal connectivity framework - a multivariate extension of the univariate fractional Gaussian noise model, which relies on a wavelet formulation for robust parameter estimation. We applied this framework to fMRI data acquired from healthy young adults at rest and while performing a visual detection task. First, we found that scale-invariance existed beyond univariate dynamics, being present also in bivariate cross-temporal dynamics. Second, we observed that frequencies within the scale-free range do not contribute evenly to inter-regional connectivity, with a systematically stronger contribution of the lowest frequencies, both at rest and during task. Third, in addition to a decrease of the Hurst exponent and inter-regional correlations, task performance modified cross-temporal dynamics, inducing a larger contribution of the highest frequencies within the scale-free range to global correlation. Lastly, we found that across individuals, a weaker task modulation of the frequency contribution to inter-regional connectivity was associated with better task performance manifesting as shorter and less variable reaction times. These findings bring together two related fields that have hitherto been studied separately - resting-state networks and scale-free dynamics, and show that scale-free dynamics of human brain activity manifest in cross-regional interactions as well.
authors.affiliation: CEA, NeuroSpin center, INRIA, Parietal Team, Bât. 145, F-91191 Gif-sur-Yvette, France. Electronic address: philippe.ciuciu@cea.fr.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciuciu
authors.affiliation: CNRS, UMR 5672, Physics Department, ENS Lyon, F-69007 Lyon, France.
authors.forename: Patrice
authors.initials: P
authors.lastname: Abry
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Biyu J
authors.initials: BJ
authors.lastname: He
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008297:Male; D008962:Models, Theoretical; D009434:Neural Pathways / Q000502:physiology*; D055815:Young Adult
keywords: Cross-temporal dynamics; Intrinsic brain activity; Scale-free dynamics; Task modulation; fMRI