1,073 research outputs found
Collective oscillation period of inter-coupled biological negative cyclic feedback oscillators
A number of biological rhythms originate from networks comprised of multiple
cellular oscillators. But analytical results are still lacking on the
collective oscillation period of inter-coupled gene regulatory oscillators,
which, as has been reported, may be different from that of an autonomous
oscillator. Based on cyclic feedback oscillators, we analyze the collective
oscillation pattern of coupled cellular oscillators. First we give a condition
under which the oscillator network exhibits oscillatory and synchronized
behavior. Then we estimate the collective oscillation period based on a novel
multivariable harmonic balance technique. Analytical results are derived in
terms of biochemical parameters, thus giving insight into the basic mechanism
of biological oscillation and providing guidance in synthetic biology design.Comment: arXiv admin note: substantial text overlap with arXiv:1203.125
Realizing the physics of motile cilia synchronization with driven colloids
Cilia and flagella in biological systems often show large scale cooperative
behaviors such as the synchronization of their beats in "metachronal waves".
These are beautiful examples of emergent dynamics in biology, and are essential
for life, allowing diverse processes from the motility of eukaryotic
microorganisms, to nutrient transport and clearance of pathogens from mammalian
airways. How these collective states arise is not fully understood, but it is
clear that individual cilia interact mechanically,and that a strong and long
ranged component of the coupling is mediated by the viscous fluid. We review
here the work by ourselves and others aimed at understanding the behavior of
hydrodynamically coupled systems, and particularly a set of results that have
been obtained both experimentally and theoretically by studying actively driven
colloidal systems. In these controlled scenarios, it is possible to selectively
test aspects of the living motile cilia, such as the geometrical arrangement,
the effects of the driving profile and the distance to no-slip boundaries. We
outline and give examples of how it is possible to link model systems to
observations on living systems, which can be made on microorganisms, on cell
cultures or on tissue sections. This area of research has clear clinical
application in the long term, as severe pathologies are associated with
compromised cilia function in humans.Comment: 31 pages, to appear in Annual Review of Condensed Matter Physic
Synchronization and entrainment of coupled circadian oscillators
Circadian rhythms in mammals are controlled by the neurons located in the
suprachiasmatic nucleus of the hypothalamus. In physiological conditions, the
system of neurons is very efficiently entrained by the 24-hour light-dark
cycle. Most of the studies carried out so far emphasize the crucial role of the
periodicity imposed by the light dark cycle in neuronal synchronization.
Nevertheless, heterogeneity as a natural and permanent ingredient of these
cellular interactions is seemingly to play a major role in these biochemical
processes. In this paper we use a model that considers the neurons of the
suprachiasmatic nucleus as chemically-coupled modified Goodwin oscillators, and
introduce non-negligible heterogeneity in the periods of all neurons in the
form of quenched noise. The system response to the light-dark cycle periodicity
is studied as a function of the interneuronal coupling strength, external
forcing amplitude and neuronal heterogeneity. Our results indicate that the
right amount of heterogeneity helps the extended system to respond globally in
a more coherent way to the external forcing. Our proposed mechanism for
neuronal synchronization under external periodic forcing is based on
heterogeneity-induced oscillators death, damped oscillators being more
entrainable by the external forcing than the self-oscillating neurons with
different periods.Comment: 17 pages, 7 figure
Synchronization and clustering of synthetic genetic networks: A role for cis-regulatory modules
The effect of signal integration through cis-regulatory modules (CRMs) on
synchronization and clustering of populations of two-component genetic
oscillators coupled by quorum sensing is in detail investigated. We find that
the CRMs play an important role in achieving synchronization and clustering.
For this, we investigate 6 possible cis-regulatory input functions (CRIFs) with
AND, OR, ANDN, ORN, XOR, and EQU types of responses in two possible kinds of
cell-to-cell communications: activator-regulated communication (i.e., the
autoinducer regulates the activator) and repressor-regulated communication
(i.e., the autoinducer regulates the repressor). Both theoretical analysis and
numerical simulation show that different CRMs drive fundamentally different
cellular patterns, such as complete synchronization, various cluster-balanced
states and several cluster-nonbalanced states.Comment: 30 pages, 8 figure
Prescription of rhythmic patterns for legged locomotion
As the engine behind many life phenomena, motor information generated by the central nervous system (CNS) plays a critical role in the activities of all animals. In this work, a novel, macroscopic and model-independent approach is presented for creating different patterns of coupled neural oscillations observed in biological central pattern generators (CPG) during the control of legged locomotion. Based on a simple distributed state machine, which consists of two nodes sharing pre-defined number of resources, the concept of oscillatory building blocks (OBBs) is summarised for the production of elaborated rhythmic patterns. Various types of OBBs can be designed to construct a motion joint of one degree-of-freedom (DOF) with adjustable oscillatory frequencies and duty cycles. An OBBs network can thus be potentially built to generate a full range of locomotion patterns of a legged animal with controlled transitions between different rhythmic patterns. It is shown that gait pattern transition can be achieved by simply changing a single parameter of an OBB module. Essentially this simple mechanism allows for the consolidation of a methodology for the construction of artificial CPG architectures behaving as an asymmetric Hopfield neural network. Moreover, the proposed CPG model introduced here is amenable to analogue and/or digital circuit integration
Chimeras in Leaky Integrate-and-Fire Neural Networks: Effects of Reflecting Connectivities
The effects of nonlocal and reflecting connectivity are investigated in
coupled Leaky Integrate-and-Fire (LIF) elements, which assimilate the exchange
of electrical signals between neurons. Earlier investigations have demonstrated
that non-local and hierarchical network connectivity often induces complex
synchronization patterns and chimera states in systems of coupled oscillators.
In the LIF system we show that if the elements are non-locally linked with
positive diffusive coupling in a ring architecture the system splits into a
number of alternating domains. Half of these domains contain elements, whose
potential stays near the threshold, while they are interrupted by active
domains, where the elements perform regular LIF oscillations. The active
domains move around the ring with constant velocity, depending on the system
parameters. The idea of introducing reflecting non-local coupling in LIF
networks originates from signal exchange between neurons residing in the two
hemispheres in the brain. We show evidence that this connectivity induces novel
complex spatial and temporal structures: for relatively extensive ranges of
parameter values the system splits in two coexisting domains, one domain where
all elements stay near-threshold and one where incoherent states develop with
multileveled mean phase velocity distribution.Comment: 12 pages, 12 figure
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