Noise-enhanced energy transduction of molecular machinery

Noise effect on persistence of memory in a positive-feedback gene regulatory circuit

Feedback circuits are important building blocks of gene regulatory network. Recent studies with simplified models found the advantage of coupled fast and slow feedback loops in creating bistable switch, and interlinked dual-time feedback loops can enhance robustness to stochasticity and persistence of memory. Based on the same feedback structure and mathematical model, the effect of noise on persistence of memory is investigated. It is found that (1) an intermediate amount of single-parameter noise plays a constructive role in persisting memory through noise-induced changing from monostable to bistable region, while larger single-parameter noise destroys the memory ability of the system through noise-induced transition between two stable states. (2) Different from the single-parameter noise, arbitrary amount of the internal noise destroys the memory ability of the system. (3) For the same feedback structure with less nonlinear feedback which is not enough to render the system bistability, the single-parameter noise can play similar constructive role through rendering the system bistability.

Multiplicative-noise-induced coherence resonance via two different mechanisms in bistable neural models

The bistable FitzHugh-Nagumo (FHN) neural model driven by two multiplicative noises and one additive noise is investigated. Two different potential mechanisms for enhancing coherence of bistable FHN model are presented, that is, the first multiplicative noise changes the system from the bistable to the oscillatory regime, and the second multiplicative noise can enhance the symmetry of two stable states of the system. The two mechanisms are analytically or numerically explained. At any level of the second multiplicative noise, a maximal coherence have been found at some intermediate noise intensity of the first multiplicative noise. Only when the first multiplicative noise intensity is less than 0.0001 can a maximal coherence be obtained at some intermediate noise intensity of the second multiplicative noise. These coherence resonance phenomena have been understood in terms of the presented mechanisms.

Coupling effects on energy transduction in coupled polymer chains with perturbation of noise

Noise-assistant transduction was investigated in coupled polymer chains where one subsystem was exposed to environment noise. It was found that coupling could transfer oscillation from one subsystem disturbed by noise to the other not disturbed by noise and play a role of a noise filtering for the other. Then, a sort of coupling-induced synchronization was investigated as a function of noise intensity and coupling strength. In particular, we calculated the minimum coupling strength to reach synchronization and pointed out that noise dominated at small coupling strength, otherwise, coupling dominated.

Critical threshold of noise-induced energy transduction in molecular machinery system

Responses of energy transduction of molecular machinery to random perturbation were investigated at the conditions where the system stayed near the bifurcation point. It was found that noise-induced oscillation (NIO) could occur. But how far from bifurcation point could one get the admissible region of NIO? We proposed and demonstrated numerically that there existed a critical threshold of NIO for each fixed noise intensity. Furthermore, it was found that noise intensity was a key factor for the determination of critical threshold. Finally, the detailed bifurcation diagram depending on noise intensity was replotted.

Signal transduction in a coupled hormone system: selective explicit internal signal stochastic resonance and its control

Cooperative interactions of signal transduction and environmental noise are investigated with a coupled hormone system, in which selective explicit internal signal stochastic resonance (EISSR) is observed. More specifically, the large peak of a period-2 oscillation (i.e., a strong signal) is greatly amplified by the environmental noise while the small peak (i.e., a weak signal) does not exhibit cooperative interactions with noise. The EISSR phenomenon could be controlled by adjusting the frequency or amplitude of an external signal and a critical amplitude for external signal is found. Significantly, the maximal signal-to-noise ratio increases almost linearly with the increment of control parameter, despite that the magnitude of the large peak is decreased. In addition, the noise does not alter the fundamental frequencies of the strong signal and the weak signal, which implicates that the system can keep its intrinsic oscillatory state and resist the effect of environmental fluctuations.

Light-noise-induced suprathreshold circadian oscillations and coherent resonance in Drosophila

Based on a reduced circadian oscillator model in Drosophila [Smolen, Biophys. J. 83, 2349 (2002)], the effects of light noise and time delay on a circadian oscillator near a Hopf bifurcation are studied by using numerical computation. When the light-controlled parameter is suprathreshold, it was found that the circadian oscillations can be induced by light fluctuation. There is an optimal light noise intensity at which a remarkable coherent circadian oscillation is observed, which implies a significant resonance phenomenon in the sense of preferred biological circadian oscillations. Time delay can control the coherence of noise-induced circadian oscillations and the strength of coherent resonance achieves a maximum under a moderate time delay.

Controlling of explicit internal signal stochastic resonance by external signal

Explicit internal signal stochastic resonance (EISSR) is investigated in a model of energy transduction of molecular machinery when noise is added to the region of oscillation in the presence of external signal (ES). It is found that EISSR could be controlled, i.e., enhanced or suppressed by adjusting frequency (omega(e)) and amplitude (A) of ES, and that there exits an optimal frequency for ES, which makes EISSR strength reach the maximum. Meanwhile, a critical amplitude (A(c)) is found, which is a threshold of occurrence of EISSR. Finally, the difference and similarity between EISSR and IISSR (implicit internal signal stochastic resonance) are discussed.