The role of the circadian system in fractal neurophysiological control

• Published in: Biological reviews of the Cambridge Philosophical Society Vol. 88; no. 4; pp. 873 - 894
• Main Authors: Pittman-Polletta, Benjamin R., Scheer, Frank A. J. L., Butler, Matthew P., Shea, Steven A., Hu, Kun
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.11.2013
• Subjects: Adaptability; Animals; Biological Clocks - physiology; Biology; Central Nervous System - physiology; circadian biology; Circadian rhythm; Circadian rhythms; Fluctuations; fractal fluctuations; fractal physiology; Fractals; Heart rate; Neurophysiology; nonlinear dynamics; Pathology; physiological control; Physiology; scale-invariance; spontaneous motor activity; suprachiasmatic nucleus; heart rate; fractal fluctuations; spontaneous motor activity; physiological control; fractal physiology; suprachiasmatic nucleus; nonlinear dynamics; circadian biology; scale-invariance
• ISSN: 1464-7931; 1469-185X; 1469-185X
• DOI: 10.1111/brv.12032

ABSTRACT Many neurophysiological variables such as heart rate, motor activity, and neural activity are known to exhibit intrinsic fractal fluctuations – similar temporal fluctuation patterns at different time scales. These fractal patterns contain information about health, as many pathological conditions are accompanied by their alteration or absence. In physical systems, such fluctuations are characteristic of critical states on the border between randomness and order, frequently arising from nonlinear feedback interactions between mechanisms operating on multiple scales. Thus, the existence of fractal fluctuations in physiology challenges traditional conceptions of health and disease, suggesting that high levels of integrity and adaptability are marked by complex variability, not constancy, and are properties of a neurophysiological network, not individual components. Despite the subject's theoretical and clinical interest, the neurophysiological mechanisms underlying fractal regulation remain largely unknown. The recent discovery that the circadian pacemaker (suprachiasmatic nucleus) plays a crucial role in generating fractal patterns in motor activity and heart rate sheds an entirely new light on both fractal control networks and the function of this master circadian clock, and builds a bridge between the fields of circadian biology and fractal physiology. In this review, we sketch the emerging picture of the developing interdisciplinary field of fractal neurophysiology by examining the circadian system's role in fractal regulation.