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Gates and Oscillators II: Zeitgebers and the Network Model of the Brain ClockDepartments of Psychology and Pharmacology & Therapeutics, University of Calgary, Calgary, AB, Canada; Department of Psychology, Columbia University, New York, NY; Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4; antlem{at}ucalgary.ca
Department of Psychology, Barnard College, New York, NY
Department of Economics, New School for Social Research, New York, NY
Department of Psychology, Columbia University, New York, NY; Department of Psychology, Barnard College, New York, NY; Department of Cell Biology and Pathology, College of Physicians and Surgeons, Columbia University, New York, NY Circadian rhythms in physiology and behavior are regulated by the SCN. When assessed by expression of clock genes, at least 2 distinct functional cell types are discernible within the SCN: nonrhythmic, light-inducible, retinorecipient cells and rhythmic autonomous oscillator cells that are not directly retinorecipient. To predict the responses of the circadian system, the authors have proposed a model based on these biological properties. In this model, output of rhythmic oscillator cells regulates the activity of the gate cells. The gate cells provide a daily organizing signal that maintains phase coherence among the oscillator cells. In the absence of external stimuli, this arrangement yields a multicomponent system capable of producing a self-sustained consensus rhythm. This follow-up study considers how the system responds when the gate cells are activated by an external stimulus, simulating a response to an entraining (or phase-setting) signal. In this model, the authors find that the system can be entrained to periods within the circadian range, that the free-running system can be phase shifted by timed activation of the gate, and that the phase response curve for activation is similar to that observed when animals are exposed to a light pulse. Finally, exogenous triggering of the gate over a number of days can organize an arrhythmic system, simulating the light-dependent reappearance of rhythmicity in a population of disorganized, independent oscillators. The model demonstrates that a single mechanism (i.e., the output of gate cells) can account for not only free-running and entrained rhythmicity but also other circadian phenomena, including limits of entrainment, a PRC with both delay and advance zones, and the light-dependent reappearance of rhythmicity in an arrhythmic animal.
Key Words: zeitgeber • zeitnehmer • coupling • oscillator • synchronization
Journal of Biological Rhythms, Vol. 22, No. 1,
14-25 (2007) This article has been cited by other articles:
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