Population Oscillations Research Articles

Theta-gamma phase amplitude coupling in a hippocampal CA1 microcircuit.

Phase amplitude coupling (PAC) between slow and fast oscillations is found throughout the brain and plays important functional roles. Its neural origin remains unclear. Experimental findings are often puzzling and sometimes contradictory. Most computational models rely on pairs of pacemaker neurons or neural populations tuned at different frequencies to produce PAC. Here, using a data-driven model of a hippocampal microcircuit, we demonstrate that PAC can naturally emerge from a single feedback mechanism involving an inhibitory and excitatory neuron population, which interplay to generate theta frequency periodic bursts of higher frequency gamma. The model suggests the conditions under which a CA1 microcircuit can operate to elicit theta-gamma PAC, and highlights the modulatory role of OLM and PVBC cells, recurrent connectivity, and short term synaptic plasticity. Surprisingly, the results suggest the experimentally testable prediction that the generation of the slow population oscillation requires the fast one and cannot occur without it.

Optimizing differential equations to fit data and predict outcomes.

Many scientific problems focus on observed patterns of change or on how to design a system to achieve particular dynamics. Those problems often require fitting differential equation models to target trajectories. Fitting such models can be difficult because each evaluation of the fit must calculate the distance between the model and target patterns at numerous points along a trajectory. The gradient of the fit with respect to the model parameters can be challenging to compute. Recent technical advances in automatic differentiation through numerical differential equation solvers potentially change the fitting process into a relatively easy problem, opening up new possibilities to study dynamics. However, application of the new tools to real data may fail to achieve a good fit. This article illustrates how to overcome a variety of common challenges, using the classic ecological data for oscillations in hare and lynx populations. Models include simple ordinary differential equations (ODEs) and neural ordinary differential equations (NODEs), which use artificial neural networks to estimate the derivatives of differential equation systems. Comparing the fits obtained with ODEs versus NODEs, representing small and large parameter spaces, and changing the number of variable dimensions provide insight into the geometry of the observed and model trajectories. To analyze the quality of the models for predicting future observations, a Bayesian-inspired preconditioned stochastic gradient Langevin dynamics (pSGLD) calculation of the posterior distribution of predicted model trajectories clarifies the tendency for various models to underfit or overfit the data. Coupling fitted differential equation systems with pSGLD sampling provides a powerful way to study the properties of optimization surfaces, raising an analogy with mutation-selection dynamics on fitness landscapes.

Investigation of the Possibility of Optimizing the Interaction of NV Centers and Photons by Changing the Shape of Microresonators

The processes of relaxation and dephasing of the electronic state of a nitrogen vacancy (NV) center within the continuum approximation for the spectrum of acoustic phonons in crystalline diamond are studied in this paper. The model of mixing of the excited electronic states of the center and its effect on the Rabi oscil-lations of populations and resonant fluorescence are analyzed. The conditions under which it is possible to implement quantum one-qubit operations both in the spin and charge subspaces of an NV center are formu-lated. The optical properties of elliptical microdisks containing NV centers are simulated and the effect of asymmetry on the spectral characteristics of such microresonators is studied.

Oscillations and confluence in three-magnon scattering of ferromagnetic resonance

We have performed a time-resolved and phase-sensitive investigation of three-magnon scattering of ferromagnetic resonance (FMR) over several orders of magnitude in excitation power. We observe a regime that hosts transient oscillations of the FMR magnon population, despite higher-order magnon interactions at large powers. Also at high powers, the scattering generates $180^\circ$ phase shifts of the FMR magnons. These phase shifts correspond to reversals in the three-magnon scattering direction, between splitting and confluence. These scattering reversals are most directly observed after removing the microwave excitation, generating coherent oscillations of the FMR magnon population much larger than its steady-state value during the excitation. Our model is in strong agreement with these findings. These findings reveal the transient behavior of this three-magnon scattering process, and the nontrivial interplay between three-magnon scattering and the magnons' phases.

The expanded circuitry of hippocampal ripples and replay

The place cells and well-defined oscillatory population rhythms of the rodent hippocampus have served as a powerful model system in linking cells and circuits to memory function. While the initial three decades of place cell research primarily focused on the activity of neurons during exploration, the last twenty-five years have seen growing interest in the physiology of the hippocampus at rest. During slow-wave sleep and quiet wakefulness the hippocampus exhibits sharp-wave ripples (SWRs), short high-frequency, high-amplitude oscillations, that organize the reactivation or ‘replay’ of sequences of place cells, and interventions that disrupt SWRs impair learning. While the canonical model of SWRs generation have emphasized CA3 input to CA1 as the source of excitatory drive, recent work suggests there are multiple circuits, including the CA2 region, that can both influence, generate and organize SWRs, both from the oscillatory and information content perspectives in a task and state-dependent manner. This extended circuitry and its function must be considered for a true understanding of the role of the hippocampus in off-line processes such as planning and consolidation.

Excitation of chaotic atomic population oscillations in a spin-orbit coupled Bose-Einstein condensate with a square-wave driving

In this paper, we have investigated the excitation of chaotic atomic population oscillations in a spin-orbit (SO) coupled Bose-Einstein condensate (BEC). Unlike previous SOC system with monochrome and bichromatic driving, the present system reveals the chaotic excitation induced by the initial condition in the nondissipative regime and by the driving strength in the dissipative regime under the action of a square-wave driving. The damping-dependent chaotic parameter regions and the modulation of atomic population oscillations by the square-wave driving are studied. The existence of chaos is confirmed by computing the corresponding largest Lyapunov exponents. The results could be significant in the quantum transport of the SO coupled cold-atom system.

Probe absorption characteristics and a tunable susceptibility switch of a superconducting flux qubit coupled to two mechanical resonators

A scheme is proposed for exploring the absorption spectrum and the susceptibility of a loop-coupled hybrid system in which two mechanical resonators are coupled to a superconducting flux qubit. Theoretical analysis has shown that the transparency based on mechanically induced coherent population oscillation (MICPO) can be tuned by the Rabi frequency and the decay rate of the mechanical resonator. We put forward a new and precise scheme to measure the frequency of the mechanical resonator. Moreover, a method to design the nonlinear susceptibility switches is also provided. Simultaneously, the coupling strength between two mechanical resonators can be detected from the distance of two peaks in the probe spectrum. The study is of great significance to the fields of precision measurement and quantum information processing.

Irregular population cycles driven by environmental stochasticity and saddle crawlbys

Despite considerable study of population cycles, the striking variability of cycle periods in many cyclic populations has received relatively little attention. Mathematical models of cyclic population dynamics have historically exhibited much greater regularity in cycle periods than many real populations, even when accounting for environmental stochasticity. We contend, however, that the recent focus on understanding the impact of long, transient but recurrent epochs within population oscillations points the way to a previously unrecognized means by which environmental stochasticity can create cycle period variation. Specifically, consumer–resource cycles that bring the populations near a saddle point (a combination of population sizes toward which the populations tend, before eventually transitioning to substantially different levels) may be subject to a slow passage effect that has been dubbed a ‘saddle crawlby'. In this study, we illustrate how stochasticity that generates variability in how close predator and prey populations come to saddles can result in substantial variability in the durations of crawlbys and, as a result, in the periods of population cycles. Our work suggests a new mechanistic hypothesis to explain an important factor in the irregular timing of population cycles and provides a basis for understanding when environmental stochasticity is, and is not, expected to generate cyclic dynamics with variability across periods.

Slow light in a 2D semiconductor plasmonic structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons interacting with excitons in a semiconductor monolayer. Here, we use coupled exciton-surface plasmon polaritons (E-SPPs) in monolayer WSe2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear E-SPP response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 105 m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.

Extreme conditions affect neuronal oscillations of cerebral cortices in humans in the China Space Station and on Earth

Rhythmical oscillations of neural populations can reflect working memory performance. However, whether neuronal oscillations of the cerebral cortex change in extreme environments, especially in a space station, remains unclear. Here, we recorded electroencephalography (EEG) signals when volunteers and astronauts were executing a memory task in extreme working conditions. Our experiments showed that two extreme conditions affect neuronal oscillations of the cerebral cortex and manifest in different ways. Lengthy periods of mental work impairs the gating mechanism formed by theta-gamma phase-amplitude coupling of two cortical areas, and sleep deprivation disrupts synaptic homeostasis, as reflected by the substantial increase in theta wave activity in the cortical frontal-central area. In addition, we excluded the possibility that nutritional supply or psychological situations caused decoupled theta-gamma phase-amplitude coupling or an imbalance in theta wave activity increase. Therefore, we speculate that the decoupled theta-gamma phase-amplitude coupling detected in astronauts results from their lengthy periods of mental work in the China Space Station. Furthermore, comparing preflight and inflight experiments, we find that long-term spaceflight and other hazards in the space station could worsen this decoupling evolution. This particular neuronal oscillation mechanism in the cerebral cortex could guide countermeasures for the inadaptability of humans working in spaceflight.

When growing pains and sick days collide: infectious disease can stabilize host population oscillations caused by stage structure

When growing pains and sick days collide: infectious disease can stabilize host population oscillations caused by stage structure

Electromagnetically Induced Grating of Surface Polaritons via Coherent Population Oscillation

We propose a scheme to study the electromagnetically induced grating (EIG) of surface polaritons (SPs) in a negative index metamaterial/rare-earth-ion-doped crystal interface waveguide system, based on coherent population oscillation (CPO) modulating by a standing wave control field. Absorption grating can be formed via the large absorption modulation induced by the linear susceptibility of the system; the diffraction of SPs can be realized but with a very small first-order diffraction efficiency and the phase modulation in this case, is negligible. However, when the giant Kerr nonlinearity is taken into account, the phase modulation can be significantly enhanced and accompanied by high transmission at the same time, thus, a phase grating, which effectively diffracts SPs into a high-order direction, can be induced. For both the absorption and phase grating, the dependencies of the first-order diffraction efficiency on the Rabi frequency of the standing wave control field, optical detuning, and interaction length are discussed. The results obtained here have certain theoretical significance for spectral enhancements and precision measurements at the micro–nanoscales.

Exciton Controlled-NOT Gate Using Coupled Quantum Dots in Carbon Nanotube

A four-level system is a prerequisite for the controlled-NOT (CNOT) gate and is realized with excitons confined in the coupled quantum dots (QDs). The coupled QDs are fabricated by chemically bonding the collagen model peptides to a single-walled carbon nanotube. An interdot exciton–exciton interaction and an exciton four-level system based on it are confirmed through photoluminescence measurements. Rabi oscillations of the exciton populations are observed, which allow the manipulations of the exciton four-level system with designed laser-pulse sequences. The tests on whether the exciton four-level system operates as a CNOT gate are conducted, and the quantum process fidelity is estimated to be approximately 0.7–0.8. The SWAP operation is also demonstrated by employing the CNOT gate three times.

Non-genetic resistance facilitates survival while hindering the evolution of drug resistance due to intraspecific competition

Rising rates of resistance to antimicrobial drugs threaten the effective treatment of infections across the globe. Drug resistance has been established to emerge from non-genetic mechanisms as well as from genetic mechanisms. However, it is still unclear how non-genetic resistance affects the evolution of genetic drug resistance. We develop deterministic and stochastic population models that incorporate resource competition to quantitatively investigate the transition from non-genetic to genetic resistance during the exposure to static and cidal drugs. We find that non-genetic resistance facilitates the survival of cell populations during drug treatment while hindering the development of genetic resistance due to competition between the non-genetically and genetically resistant subpopulations. Non-genetic resistance in the presence of subpopulation competition increases the fixation times of drug resistance mutations, while increasing the probability of mutation before population extinction during cidal drug treatment. Intense intraspecific competition during drug treatment leads to extinction of susceptible and non-genetically resistant subpopulations. Alternating between drug and no drug conditions results in oscillatory population dynamics, increased resistance mutation fixation timescales, and reduced population survival. These findings advance our fundamental understanding of the evolution of resistance and may guide novel treatment strategies for patients with drug-resistant infections.

Global stability and oscillations for mosquito population models with diapausing stages

In this paper we analyze the dynamical behavior of a mosquito population with diapausing stages through a mathematical model derived from the classical McKendrick-von Forester equations. The absence of monotonicity properties and the structure of the equations are noticeable features that hinder the use of commonly applied tools in the field. Our main contribution is to provide a novel methodology to derive criteria of global attractivity of a positive solution for periodic and discontinuous delay differential equations. From an applied perspective, we simulate the evolution of Aedes aegypti with diapausing stages. Moreover, we discuss the influence of the diapause parameters on the creation/suppression of population oscillations.

Sulfur Geochemistry Destabilizes Population Oscillations of Wild Rice (Zizania palustris)

AbstractElevated inputs of sulfate to freshwater systems can increase sulfide concentrations in anoxic soils and subsequently destabilize aquatic plant populations, but the interactions between sulfate, other geochemical cycles, and interannual plant population cycles are poorly understood. Increased sulfate loading increases mineralization of nitrogen from litter, but the sulfide produced during this process can limit nitrogen uptake by plants. In some cases, iron may mitigate sulfide's impacts on plants by precipitating iron sulfide. We examined the interannual effects of sulfate loading on mesocosm populations of wild rice, an emergent aquatic plant that undergoes population oscillations and is sensitive to sulfide. Using experimental mesocosms with self‐perpetuating populations, we investigated how population dynamics respond to manipulations of surface water sulfate (10 mg L−1 or 300 mg L−1), sediment iron (4.3 mg g−1 or 10.9 mg g−1 dry weight), and shoot litter (present or removed). Populations exposed to constant 10 mg L−1 sulfate concentrations had stable biomass oscillations of approximately 3‐year periods, consistent with previous studies that demonstrated litter‐driven oscillations in nitrogen availability. Populations exposed to 300 mg L−1 sulfate concentrations produced fewer and smaller seeds and declined to extinction in 6 years or less. We did not find a strong effect of iron loading or litter removal on wild rice biomass or seed production. Our observations show the potential of elevated surface water sulfate to rapidly destabilize wild rice populations under varying iron and organic carbon concentrations.

Effect of detuning on velocity-induced population oscillation

Effect of detuning on velocity-induced population oscillation

Are there plenty of fish in the sea? How life history traits affect the eco-evolutionary consequences of population oscillations

Understanding fish population oscillations is important for both fundamental population biology and for fisheries science. Much research has focused on the causes of population oscillations, but the eco-evolutionary consequences of population oscillations are unclear. Here, we used an empirically parametrised individual-based simulation model to explore the consequences of oscillations with different amplitudes and wavelengths. We show that oscillations with a wavelength shorter than the maximum lifespan of the fish produce marked differences in the evolutionary trajectories of asymptotic length. Wavelengths longer than the maximum lifespan of the fish, in turn, mainly manifest as ecological effects seen as the population biomass oscillation. The evolutionary and ecological differences increase with increasing amplitude, however, the two-year wavelength causes opposing results from all the other scenarios. This is likely facilitated by the relatively stable number of fish in the population as a poor year is always counteracted by the previous good year and vice versa. Our results highlight the evolutionary signatures and following ecological consequences that natural population oscillations can cause.

Theoretical study on fast and slow light effects in semiconductor optical amplifiers under assist light injection

In this paper, the fast and slow light effect of semiconductor optical amplifiers (SOAs) under assist light injection is theoretically analyzed. Coherent population oscillation (CPO) is used to induce fast and slow light effect in the theoretical model. The effects of parameters such as modulation frequency, modulation current and assist optical power on phase delay are investigated under the assist light injection. These effects are then compared with the case without assist light injection. The simulation results show that the injection of assist light can increase the phase delay of the output optical signal and enhance the slow light effect. Furthermore, when the assist light optical power is in the range of 0–15 dBm, the slow light effect is strong.

Reconstruction of attosecond beating by interference of two-photon transitions on the lithium atom with Rabi oscillations

We present numerical simulations of the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) on lithium by solving the three-dimensional time-dependent Schr\"odinger equation. In our scheme, the infrared (IR) field couples the $2s$ and $2p$ states of lithium and leads to the Rabi oscillations of populations between these two states. We analyzed the RABBITT phases of the two peaks in the Rabi-oscillation-induced Autler-Townes splittings. Our results show that the relative phase between these two peaks changes with the photoelectron energy and depends on the intensity of the IR field. Moreover, in the angle-resolved RABBITT measurement, the phases of the two peaks depend differently on the emission angle of photoelectrons. These behaviors are traced back to the different initial phases of the electron wave packets emitted from the dressed $2p$ states and the competition among different ionization channels.