title: The suprachiasmatic nucleus functions beyond circadian rhythm generation.
abstract: We recently discovered that human activity possesses a complex temporal organization characterized by scale-invariant/self-similar fluctuations from seconds to approximately 4 h-(statistical properties of fluctuations remain the same at different time scales). Here, we show that scale-invariant activity patterns are essentially identical in humans and rats, and exist for up to approximately 24 h: six-times longer than previously reported. Theoretically, such scale-invariant patterns can be produced by a neural network of interacting control nodes-system components with feedback loops-operating at different time scales. However such control nodes have not yet been identified in any neurophysiological model of scale invariance/self-similarity in mammals. Here we demonstrate that the endogenous circadian pacemaker (suprachiasmatic nucleus; SCN), known to modulate locomotor activity with a periodicity of approximately 24 h, also acts as a major neural control node responsible for the generation of scale-invariant locomotor patterns over a broad range of time scales from minutes to at least 24 h (rather than solely at approximately 24 h). Remarkably, we found that SCN lesion in rats completely abolished the scale-invariant locomotor patterns between 4 and 24 h and significantly altered the patterns at time scales <4 h. Identification of the control nodes of a neural network responsible for scale invariance is the critical first step in understanding the neurophysiological origin of scale invariance/self-similarity.
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital, Sleep Disorders @BIDMC, 75 Francis Street, Boston, MA 02215, USA. khu@bidmc.harvard.edu
authors.forename: K
authors.initials: K
authors.lastname: Hu
authors.forename: F A J L
authors.initials: FA
authors.lastname: Scheer
authors.forename: P Ch
authors.initials: PCh
authors.lastname: Ivanov
authors.forename: R M
authors.initials: RM
authors.lastname: Buijs
authors.forename: S A
authors.initials: SA
authors.lastname: Shea
mesh_terms: D000204:Activity Cycles / Q000502:physiology; D000328:Adult; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D009043:Motor Activity / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013493:Suprachiasmatic Nucleus / Q000502:physiology*