The meningeal lymphatic vessels were discovered 2 years ago as the drainage system involved in the mechanisms underlying the clearance of waste products from the brain. The blood–brain barrier (BBB) is a gatekeeper that strongly controls the movement of different molecules from the blood into the brain. We know the scenarios during the opening of the BBB, but there is extremely limited information on how the brain clears the substances that cross the BBB. Here, using the model of sound-induced opening of the BBB, we clearly show how the brain clears dextran after it crosses the BBB via the meningeal lymphatic vessels. We first demonstrate successful application of optical coherence tomography (OCT) for imaging of the lymphatic vessels in the meninges after opening of the BBB, which might be a new useful strategy for noninvasive analysis of lymphatic drainage in daily clinical practice. Also, we give information about the depth and size of the meningeal lymphatic vessels in mice. These new fundamental data with the applied focus on the OCT shed light on the mechanisms of brain clearance and the role of lymphatic drainage in these processes that could serve as an informative platform for a development of therapy and diagnostics of diseases associated with injuries of the BBB such as stroke, brain trauma, glioma, depression, or Alzheimer disease.
We study the noise activated dynamics of a model autapse neuron system that consists of a subcritical Hopf oscillator with
a time delayed nonlinear feedback. The coherence of the noise driven pulses of the neuron exhibits a novel double peaked
structure as a function of the noise amplitude. The two peaks correspond to separate optimal noise levels for excitation of
single spikes and multiple spikes (bursts) respectively. The relative magnitudes of these peaks are found to be a sensitive
function of time delay. The physical significance of our results and its practical implications in various real life systems
Proc. SPIE. 5471, Noise in Complex Systems and Stochastic Dynamics II
KEYWORDS: Homogenization, Diffusion, Interference (communication), Control systems, Wave propagation, Chemical reactions, Error control coding, Stochastic processes, Systems modeling, Information operations
Constructive effects of noise have been well studied in spatially extended systems. In most of these studies, the media are static, reaction-diffusion type, and the constructive effects are a consequence of the interplay between local excitation due to noise perturbation and propagation of excitation due to diffusion. Many chemical or biological processes occur in a fluid environment with mixing. In this paper, we investigate the interplay among noise, excitability, diffusion and mixing in excitable media advected by a chaotic flow, in a 2D Fitz Hugh-Nagumo model described by a set of reaction-advection-diffusion equations. Without stirring, noise can only generate non-coherent excited patches of the static media. In the presence of stirring, we observe three dynamical and pattern formation regimes: (1) Non-coherent excitation, when mixing is not strong enough to achieve synchronization of independent excitations developed at different locations; (2) Coherent global excitation, when the noise-induced perturbation propagates by mixing and generates a synchronized excitation of the whole domain; and (3) Homogenization, when strong stirring dilutes quickly those noise-induced local excitations. In the presence of an external sub-threshold periodic forcing, the period of the noise-sustained oscillations can be locked by the forcing period with different ratios. Our results may be verified in experiments and find applications in population dynamics of oceanic ecological systems.
A noise-induced signal propagation is reported in oscillatory
media with FitzHugh-Nagumo dynamics which is based on a noise-induced phase transition to excitability. This transition occurs
via a noise-induced suppression of self-excited oscillations, while the overall phase-space structure of the system is maintained. The noise-induced excitability enables the information transport in the originally oscillatory media. We demonstrate this new feature by the propagation of a wave front and the formation of a spiral in a two dimensional lattice. These spatio-temporal structures transport information and can be observed only in the presence of suitable amount of noise and not in the deterministic self-sustained oscillatory system. Thus we extend classes of nonlinear systems with signal transmission properties also to oscillatory systems, which demonstrate a noise-induced phase transition to excitability. Further on, the mechanism of noise-induced excitability provides the opportunity to control the information transport by noise via a triggering mechanism, i.e. the information channel is switched on in the presence of noise and switched off in its absence.
We study nonlinear systems under two noisy sources to demonstrate the concept of doubly stochastic effects. In such effects noise plays a twofold role: first it induces a special feature in the system, and second it interplays with this feature leading to noise-induced order. For this effect one needs to optimize both noisy sources, hence we call these phenomena doubly stochastic effects. To show the generality of this approach we apply this concept to several basic noise-induced phenomena: stochastic resonance, noise-induced propagation and coherence resonance. Additionally, we discuss an application of this concept to noise-induced transitions and ratchets. In all these noise-induced effects ordering occurs due to the joint action of two noisy sources.