FitzHugh-Nagumo System Research Articles

Dynamical behaviors of non-autonomous fractional FitzHugh-Nagumo system driven by additive noise in unbounded domains

The regularity of random attractors is considered for the non-autonomous fractional stochastic FitzHugh-Nagumo system. We prove that the system has a pullback random attractor that is compact in Hs(ℝn) × L2(ℝn) and attracts all tempered random sets of L2(ℝn) × L2(ℝn) in the topology of Hs(ℝn) × L2(ℝn) with s ∈ (0, 1). By the idea of positive and negative truncations, spectral decomposition in bounded domains, and tail estimates, we achieved the desired results.

A Remark on the Meromorphic Solutions in the FitzHugh–Nagumo Model

Due to the Nevanlinna theory, the paper gives the general structure of transcendental meromorphic solutions of a certain ordinary differential equation with rational coefficients. As an application, the meromorphic solutions of the FitzHugh–Nagumo system are obtained in explicit form.

Dynamics of the FitzHugh–Nagumo system having invariant algebraic surfaces

In this paper, we study the dynamics of the FitzHugh–Nagumo system $$\dot{x}=z,\;\dot{y}=b\left( x-dy\right) ,\;\dot{z}=x\left( x-1\right) \left( x-a\right) +y+cz$$ having invariant algebraic surfaces. This system has four different types of invariant algebraic surfaces. The dynamics of the FitzHugh–Nagumo system having two of these classes of invariant algebraic surfaces have been characterized in Valls (J Nonlinear Math Phys 26:569–578, 2019). Using the quasi-homogeneous directional blow-up and the Poincaré compactification, we describe the dynamics of the FitzHugh–Nagumo system having the two remaining classes of invariant algebraic surfaces. Moreover, for these FitzHugh–Nagumo systems we prove that they do not have limit cycles.

Dynamics for stochastic Fitzhugh–Nagumo systems with general multiplicative noise on thin domains

This paper is devoted to studying the dynamics for stochastic Fitzhugh–Nagumo equations with general multiplicative noise on thin domains, where the noise is described by a general stochastic process instead of the usual Wiener process. The measurability of the solution operator is proved, which yields to the measurability of the random attractor. We then show the existence and upper semi‐continuity of these attractors when a family of (n + 1)‐dimensional thin domains degenerates onto an n‐dimensional domain under the topology of p‐times Lebesgue space.

Global bifurcation studies of a cubic Liénard system

In recent decades much attention has been paid to polynomial Liénard systems. Cubic ones are such systems with a cubic restoring and quadratic damping; for example, the famous FitzHugh-Nagumo system can be transformed into a cubic Liénard system. For the three-parameter family of cubic Liénard systems, the case with a positive restoring leading coefficient was solved except the maximum number of limit cycles remains open when the system has a unique equilibrium. In this paper we will investigate the case when the leading coefficient of the restoring is negative, we will show that saddle-node bifurcations, pitchfork bifurcations, Hopf bifurcations, homoclinic bifurcations, and heteroclinic bifurcations will occur through a global analysis and present a global bifurcation diagram with global phase portraits depicted in Poincaré disks. Finally, some main results are demonstrated by numerical simulations.

Mathematical modeling of depressive disorders: Circadian driving, bistability and dynamical transitions

The hypothalamus–pituitary–adrenal (HPA) axis is a key neuroendocrine system implicated in stress response, major depression disorder, and post-traumatic stress disorder. We present a new, compact dynamical systems model for the response of the HPA axis to external stimuli, representing stressors or therapeutic intervention, in the presence of a circadian input. Our work builds upon previous HPA axis models where hormonal dynamics are separated into slow and fast components. Several simplifications allow us to derive an effective model of two equations, similar to a multiplicative-input FitzHugh-Nagumo system, where two stable states, a healthy and a diseased one, arise. We analyze the effective model in the context of state transitions driven by external shocks to the hypothalamus, but also modulated by circadian rhythms. Our analyses provide mechanistic insight into the effects of the circadian cycle on input driven transitions of the HPA axis and suggest a circadian influence on exposure or cognitive behavioral therapy in depression, or post-traumatic stress disorder treatment.

Phase sensitivity for coherence resonance oscillators

The phase reduction approach has manifested its power in analyzing the rhythmic behaviors for limit cycle oscillators. For coherent oscillation purely induced by noise, e.g., the coherence resonance oscillator, the stochastic dynamics exhibit almost deterministic limit cycle phenomenon which inspires the application of the phase reduction approach to this kind of systems. In this paper, the FitzHugh–Nagumo system in coherence resonance is modeled as a jump process. The phase sensitivity is obtained by applying the phase reduction approach for the hybrid system. A modified direct method is proposed to compare the theoretical results with those of Monte Carlo simulation for the stochastic system, which shows a relatively good agreement for the perturbation not being too small. The phase reduction results of the coherent oscillators are applied to two coupled FitzHugh–Nagumo neurons. It is interesting that the phase difference of the coupled coherent oscillators does not converge as the deterministic oscillators, but forms a distribution where the peaks and valleys correspond to the stable and unstable synchronizations predicted by the phase coupling functions. The idea in this paper could be applied to other coherent oscillators where the stochastic dynamics follow almost deterministic paths.

Random uniform attractor and random cocycle attractor for non-autonomous stochastic FitzHugh–Nagumo system on unbounded domains

In this paper, we introduce the concept of uniform pullback asymptotic compactness of a non-autonomous random dynamical system, and prove the existence of random uniform and cocycle attractor with autonomous attraction universes for non-autonomous stochastic FitzHugh–Nagumo system with multiplicative noise defined on whole space. Some properties of random uniform and cocycle attractor are shown. The method of tail estimates plays an important role.

Well-posedness and dynamics of fractional FitzHugh-Nagumo systems on ℝN driven by nonlinear noise

This article is concerned with the well-posedness as well as long-term dynamics of a wide class of non-autonomous, non-local, fractional, stochastic FitzHugh-Nagumo systems driven by nonlinear noise defined on the entire spaceℝRN. The well-posedness is proved for the systems with polynomial drift terms of arbitrary order as well as locally Lipschitz nonlinear diffusion terms by utilizing the pathwise and mean square uniform estimates. The mean random dynamical system generated by the solution operators is proved to possess a unique weak pullback mean random attractor in a Bochner space. The existence of invariant measures is also established for the autonomous systems with globally Lipschitz continuous diffusion terms. The idea of uniform tail-estimates of the solutions in the appropriate spaces is employed to derive the tightness of a family of probability distributions of the solutions in order to overcome the non-compactness of the standard Sobolev embeddings on ℝN as well as the lack of smoothing effect on one component of the solutions. The results of this paper are new even when the fractional Laplacian is replaced by the standard Laplacian.

Chimera states in ensembles of excitable FitzHugh–Nagumo systems

An ensemble of nonlocally coupled excitable FitzHugh-Nagumo systems is studied. In the presence of noise the explored system can exhibit a special kind of chimera states called coherence-resonance chimera. As previously thought, noise plays principal role in forming these structures. It is shown in the present paper that these regimes appear because of the specific coupling between the elements. The action of coupling involve a spatial wave regime, which occurs in ensemble of excitable nodes even if the noise is switched off. In addition, a new chimera state is obtained in an excitable regime. It is shown that the noise makes this chimera more stable near an Andronov-Hopf bifurcation.

Bifurcation delay, travelling waves and chimera-like states in a network of coupled oscillators

We report novel bifurcation delays and chimera-like states in a network of driven FitzHugh-Nagumo (FHN) oscillators, where each oscillator can rotate either clockwise or anticlockwise. Slow variation of the time-dependent parameter of FHN oscillator near the bifurcation point leads to a delay in the bifurcation. The time delay in the bifurcation is independent of the direction of rotation of the system (clockwise or anticlockwise rotation). When the FHN oscillators are coupled via dissimilar variables, then bifurcation delay in the anticlockwise rotating oscillator changes, creating chimera-like structures and also travelling waves at certain coupling strength. Bifurcation preponement is also observed for other range of coupling strengths. Similar results are also observed in networks of van der Pol and Landau-Stuart oscillators suggesting that the phenomenon is general rather than specific to coupled FHN systems.

Regular dynamics for stochastic Fitzhugh-Nagumo systems with additive noise on thin domains

<p style='text-indent:20px;'>This paper is devoted to bi-spatial random attractors of the stochastic Fitzhugh-Nagumo equations with additive noise on thin domains when the terminate space is the Sobolev space. We first established the existence of random attractor on regular space and then show that the upper semi-continuity of these attractors under the Sobolev norm when a family of <inline-formula><tex-math id="M1">\begin{document}$ (n+1) $\end{document}</tex-math></inline-formula>-dimensional thin domains degenerates onto an <inline-formula><tex-math id="M2">\begin{document}$ n $\end{document}</tex-math></inline-formula>-dimensional domain.

An efficient parameter estimation method for nonlinear high-order systems via surrogate modeling and cuckoo search

This work developed an efficient parameter estimation method for nonlinear high-order systems using surrogate modeling and cuckoo search. Specifically, to address the heavy computational burden required for evaluating the candidate parameters, we utilized a low-dimensional surrogate model to approximate the original system. The surrogate model was constructed by employing the proper orthogonal decomposition and the discrete empirical interpolation method. Then, to obtain the parameters of the original system, we applied the cuckoo search algorithm to solve the optimization problem that was built on the surrogate model. The accuracy and efficiency of the proposed method were verified on two numerical experiments, dealing with the identification of parameters for the FitzHugh–Nagumo system and the predator–prey system. The results showed that our approach yields accurate results while significantly reducing the computational cost.

Attractors for FitzHugh-Nagumo lattice systems with almost periodic nonlinear parts

For FitzHugh-Nagumo lattice dynamical systems (LDSs) many authors studied the existence of global attractors for deterministic systems [4,34,41,43] and the existence of global random attractors for stochastic systems [23,24,27,48,49], where for non-autonomous cases, the nonlinear parts are considered of the form $ f\left( u\right) $. Here we study the existence of the uniform global attractor for a new family of non-autonomous FitzHugh-Nagumo LDSs with nonlinear parts of the form $ f\left( u,t\right) $, where we introduce a suitable Banach space of functions $ W $ and we assume that $ f $ is an element of the hull of an almost periodic function $ f_{0}\left( \cdot ,t\right) $ with values in $ W $.

Stabilities and dynamic transitions of the Fitzhugh-Nagumo system

<p style='text-indent:20px;'>The article aims to examine the dynamic transition of the reaction-diffusion Fitzhugh-Nagumo system defined on a thin spherical shell and a 2D-rectangular domain. The mathematical tool employed is the theory of phase transition dynamics established for dissipative dynamical systems. The main results in this paper include two parts. First, for the system on a thin spherical shell, we only focus on the transition from a real simple eigenvalue. More precisely, if the first eigenspace is three–dimensional, the system undergoes either a continuous transition or a jump transition. Besides, a mix transition is also allowed if the first eigenspace is one–dimensional. Second, for the system on a rectangular domain, both the transitions from a simple real eigenvalue and a pair of simple complex eigenvalues are considered. Our results imply that two steady-state solutions bifurcate, which are either attractors or saddle points, and a Hopf bifurcation is also possible in the system on the rectangular domain.

Existence of the solitary wave solutions supported by the modified FitzHugh–Nagumo system

We study a system of nonlinear differential equations simulating transport phenomena in active media. The model we are interested in is a generalization of the celebrated FitzHugh–Nagumo system describing the nerve impulse propagation in axon. The modeling system is shown to possesses soliton-like solutions under certain restrictions on the parameters. The results of theoretical studies are backed by the direct numerical simulation.

Chimera dynamics in an array of coupled FitzHugh-Nagumo system with shift of close neighbors

In this paper, we consider an array of FitzHugh-Nagumo (FHN) systems with R close neighbors. Each element (j) connects to another (m) and its 2R neighbors. Shifting these neighbors produces particular phenomena such as chimera and multi-chimera. Step traveling chimera is observed for a time dependent shift. Results show that, basing oneself on both shift parameter m and close neighbors R, a full control on the chimera dynamics of the network can be ensured.

A closer look at turbulence spreading: How bistability admits intermittent, propagating turbulence fronts

In magnetic fusion plasmas, mounting evidence suggests the possibility of sustained turbulence below the linear stability threshold or more generally global turbulence bistability. The usual reduced models for turbulence spreading are unistable/supercritical and incompatible with this result. The older models also cannot realistically support fronts connecting laminar and turbulent domains. In this work, a minimal model for “subcritical” turbulence spreading is introduced and analyzed. The model may be viewed as phenomenological or derived directly by considering the effect of profile corrugations in an E × B staircase. The model, which is related to the FitzHugh–Nagumo system, supports the robust coexistence of multiple turbulence levels via bistability. We show that this model predicts stronger penetration of turbulence into a linearly stable region as well as the formation of intermittent turbulence fronts that resemble avalanches. We derive the critical size that a localized slug of turbulence must exceed in order to spread. Finally, we make a prediction of global hysteretic behavior associated with the bistability, which should be testable via experiment.

Vibrational mono-/bi-resonance and wave propagation in FitzHugh–Nagumo neural systems under electromagnetic induction

In this paper, an modified FitzHugh–Nagumo (FHN) neural model was employed to investigate the vibrational resonance (VR) phenomenon, the collective behaviors, and the transmission of weak low-frequency (LF) signal driven by high-frequency (HF) stimulus under the action of different electromagnetic induction in single FHN neuron and feed-forward feedback network (FFN) system, respectively. For the single FHN system, by increasing the amplitude of HF stimulus, the phenomena of vibrational mono-/bi-resonance are observed, and the input weak signal and output of system are synchronized, and the information of the weak LF signal is amplified. For the FFN system, the phenomena of vibrational mono-/bi-resonances are also occurred, both frequency and amplitude of the HF stimulus play an important role in the vibrational bi-resonances and transmission of weak LF signal in the FHN neural FFN.

The Fitzhugh-Nagumo System as a Model of Human Cardiac Action Potentials

The Fitzhugh-Nagumo System as a Model of Human Cardiac Action Potentials