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Biology 2019, 8(1), 18; https://doi.org/10.3390/biology8010018

Telling the Time with a Broken Clock: Quantifying Circadian Disruption in Animal Models

Sleep and Circadian Neuroscience Institute (SCNi), Nuffield Department of Clinical Neurosciences, Oxford Molecular Pathology Institute, Sir William Dunn School of Pathology, South Parks Road, Oxford OX1 3RE, UK
*
Author to whom correspondence should be addressed.
These authors contributed equally.
Received: 17 December 2018 / Revised: 12 February 2019 / Accepted: 9 March 2019 / Published: 21 March 2019
(This article belongs to the Special Issue Biological Clocks)
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Abstract

Circadian rhythms are approximately 24 h cycles in physiology and behaviour that enable organisms to anticipate predictable rhythmic changes in their environment. These rhythms are a hallmark of normal healthy physiology, and disruption of circadian rhythms has implications for cognitive, metabolic, cardiovascular and immune function. Circadian disruption is of increasing concern, and may occur as a result of the pressures of our modern 24/7 society—including artificial light exposure, shift-work and jet-lag. In addition, circadian disruption is a common comorbidity in many different conditions, ranging from aging to neurological disorders. A key feature of circadian disruption is the breakdown of robust, reproducible rhythms with increasing fragmentation between activity and rest. Circadian researchers have developed a range of methods for estimating the period of time series, typically based upon periodogram analysis. However, the methods used to quantify circadian disruption across the literature are not consistent. Here we describe a range of different measures that have been used to measure circadian disruption, with a particular focus on laboratory rodent data. These methods include periodogram power, variability in activity onset, light phase activity, activity bouts, interdaily stability, intradaily variability and relative amplitude. The strengths and limitations of these methods are described, as well as their normal ranges and interrelationships. Whilst there is an increasing appreciation of circadian disruption as both a risk to health and a potential therapeutic target, greater consistency in the quantification of disrupted rhythms is needed. View Full-Text
Keywords: activity bouts; data analysis; entrainment; fragmentation; periodogram activity bouts; data analysis; entrainment; fragmentation; periodogram
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Brown, L.A.; Fisk, A.S.; Pothecary, C.A.; Peirson, S.N. Telling the Time with a Broken Clock: Quantifying Circadian Disruption in Animal Models. Biology 2019, 8, 18.

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