Abstract
The principle clock of mammals, named suprachiasmatic nucleus (SCN), coordinates the circadian rhythms of behavioral and physiological activity to the external 24 h light-dark cycle. In the absence of the daily cycle, the SCN acts as an endogenous clock that regulates the ~24h rhythm of activity. Experimental and theoretical studies usually take the light-dark cycle as a main external influence, and often ignore light pollution as an external influence. However, in modern society, the light pollution such as induced by electrical lighting influences the circadian clock. In the present study, we examined the effect of external noise (light pollution) on the collective behavior of coupled circadian oscillators under constant darkness using a Goodwin model. We found that the external noise plays distinct roles in the network behavior of neurons for weak or strong coupling between the neurons. In the case of strong coupling, the noise reduces the synchronization and the period of the SCN network. Interestingly, in the case of weak coupling, the noise induces a circadian rhythm in the SCN network which is absent in noise-free condition. In addition, the noise increases the synchronization and decreases the period of the SCN network. Our findings may shed new light on the impact of the external noise on the collective behavior of SCN neurons.
Highlights
The primary clock, which is located in the suprachiasmatic nucleus (SCN) in the brain of mammals, regulates the circadian (~24 h) rhythm in physiology and in behavioral activity[1]
We examined the effect of external noise on the collective behavior of SCN neuronal oscillators under constant darkness based on the Goodwin model
We observed that noise functions differently for strong coupling and for weak coupling
Summary
The primary clock, which is located in the suprachiasmatic nucleus (SCN) in the brain of mammals, regulates the circadian (~24 h) rhythm in physiology and in behavioral activity[1]. The SCN is composed of about twenty thousand self-oscillating neurons, with intrinsic periods ranging roughly from 22 h to 28 h[2] These non-identical neurons are coupled through neurotransmitters and neuropeptides (e.g. vasoactive intestinal polypeptide, arginine vasopressin and γ-aminobutric acid) to form an SCN network and exhibit collective behavior[3]. We use coupled Goodwin oscillators to model the SCN network under constant darkness accompanied by external noise. In the rest of this article, we will use the Goodwin model to examine the effect of the interplay between external noise and the coupling strength on network behavior of the SCN, i.e. the oscillation, the synchronization and the free running period of the SCN network
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