124 research outputs found
Collective chaos in pulse-coupled neural networks
We study the dynamics of two symmetrically coupled populations of identical
leaky integrate-and-fire neurons characterized by an excitatory coupling. Upon
varying the coupling strength, we find symmetry-breaking transitions that lead
to the onset of various chimera states as well as to a new regime, where the
two populations are characterized by a different degree of synchronization.
Symmetric collective states of increasing dynamical complexity are also
observed. The computation of the the finite-amplitude Lyapunov exponent allows
us to establish the chaoticity of the (collective) dynamics in a finite region
of the phase plane. The further numerical study of the standard Lyapunov
spectrum reveals the presence of several positive exponents, indicating that
the microscopic dynamics is high-dimensional.Comment: 6 pages, 5 eps figures, to appear on Europhysics Letters in 201
Chaos in generically coupled phase oscillator networks with nonpairwise interactions
The Kuramoto-Sakaguchi system of coupled phase oscillators, where interaction
between oscillators is determined by a single harmonic of phase differences of
pairs of oscillators, has very simple emergent dynamics in the case of
identical oscillators that are globally coupled: there is a variational
structure that means the only attractors are full synchrony (in-phase) or splay
phase (rotating wave/full asynchrony) oscillations and the bifurcation between
these states is highly degenerate. Here we show that nonpairwise coupling -
including three and four-way interactions of the oscillator phases - that
appears generically at the next order in normal-form based calculations, can
give rise to complex emergent dynamics in symmetric phase oscillator networks.
In particular, we show that chaos can appear in the smallest possible dimension
of four coupled phase oscillators for a range of parameter values
Chimera states in pulse coupled neural networks: the influence of dilution and noise
We analyse the possible dynamical states emerging for two symmetrically pulse
coupled populations of leaky integrate-and-fire neurons. In particular, we
observe broken symmetry states in this set-up: namely, breathing chimeras,
where one population is fully synchronized and the other is in a state of
partial synchronization (PS) as well as generalized chimera states, where both
populations are in PS, but with different levels of synchronization. Symmetric
macroscopic states are also present, ranging from quasi-periodic motions, to
collective chaos, from splay states to population anti-phase partial
synchronization. We then investigate the influence disorder, random link
removal or noise, on the dynamics of collective solutions in this model. As a
result, we observe that broken symmetry chimera-like states, with both
populations partially synchronized, persist up to 80 \% of broken links and up
to noise amplitudes 8 \% of threshold-reset distance. Furthermore, the
introduction of disorder on symmetric chaotic state has a constructive effect,
namely to induce the emergence of chimera-like states at intermediate dilution
or noise level.Comment: 15 pages, 7 figure, contribution for the Workshop "Nonlinear Dynamics
in Computational Neuroscience: from Physics and Biology to ICT" held in Turin
(Italy) in September 201
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
Time-delayed feedback in neurosystems
The influence of time delay in systems of two coupled excitable neurons is
studied in the framework of the FitzHugh-Nagumo model. Time-delay can occur in
the coupling between neurons or in a self-feedback loop. The stochastic
synchronization of instantaneously coupled neurons under the influence of white
noise can be deliberately controlled by local time-delayed feedback. By
appropriate choice of the delay time synchronization can be either enhanced or
suppressed. In delay-coupled neurons, antiphase oscillations can be induced for
sufficiently large delay and coupling strength. The additional application of
time-delayed self-feedback leads to complex scenarios of synchronized in-phase
or antiphase oscillations, bursting patterns, or amplitude death.Comment: 13 pages, 13 figure
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