286 results for qubit oscillator frequency
Data from: Input-dependent frequency modulation of cortical gamma oscillations shapes spatial synchronization and enables phase coding
Contributors: Lowet, Eric, Roberts, Mark, Hadjipapas, Avgis, Peter, Alina, van der Eerden, Jan, De Weerd, Peter
phase-oscillator model part 1...phase-oscillator model part 2...phase-oscillator model part 3...phase-oscillator model part 4...oscillation frequencies at nearby spatial locations. Similarly to cortical...oscillation phase codes, may resolve conflicting experimental observations...frequency with increasing input drive. The relates to the experimental...oscillators. The gamma phase-locking, the precise phase relation and the...oscillators, where input drive determines the intrinsic (natural) frequency...Frequency Modulation of Cortical Gamma Oscillations Shapes Spatial Synchronization...oscillation...frequency of gamma oscillations varies with input drive (e.g. visual contrast ... Fine-scale temporal organization of cortical activity in the gamma range (~25–80Hz) may play a significant role in information processing, for example by neural grouping (‘binding’) and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency codes or slower oscillation phase codes, may resolve conflicting experimental observations on gamma phase coding. Our modeling results offer clear testable experimental predictions. We conclude that input-dependency of gamma frequencies could be essential rather than detrimental for meaningful gamma-mediated temporal organization of cortical activity.
Data from: Detection of transient synchrony across oscillating receptors by the central electrosensory system of mormyrid fish
Contributors: Vélez, Alejandro, Carlson, Bruce A.
oscillations among receptors. We found that electrosensory stimulation...oscillating electroreceptors in weakly electric fish (Mormyridae) respond...oscillation frequencies of the receptors. These frequencies are lower ...Frequency tuning in the midbrain resembled peripheral frequency tuning ... Recently, we reported evidence for a novel mechanism of peripheral sensory coding based on oscillatory synchrony. Spontaneously oscillating electroreceptors in weakly electric fish (Mormyridae) respond to electrosensory stimuli with a phase reset that results in transient synchrony across the receptor population (Baker et al., 2015). Here, we asked whether the central electrosensory system actually detects the occurrence of synchronous oscillations among receptors. We found that electrosensory stimulation elicited evoked potentials in the midbrain exterolateral nucleus at a short latency following receptor synchronization. Frequency tuning in the midbrain resembled peripheral frequency tuning, which matches the intrinsic oscillation frequencies of the receptors. These frequencies are lower than those in individual conspecific signals, and instead match those found in collective signals produced by groups of conspecifics. Our results provide further support for a novel mechanism for sensory coding based on the detection of oscillatory synchrony among peripheral receptors.
Contributors: Bos, Hannah, Diesmann, Markus, Helias, Moritz
frequency. The low-γ peak turns out to be generated in a sub-circuit located...oscillations visible in all populations. Since locally generated frequencies...frequency of the observed oscillations and identifies the minimal circuit...Oscillations are omnipresent in neural population signals, like multi-unit...Oscillations in the Cortical Microcircuit...oscillations...frequency-dependent connectivity map that reveals connections crucial ... Oscillations are omnipresent in neural population signals, like multi-unit recordings, EEG/MEG, and the local field potential. They have been linked to the population firing rate of neurons, with individual neurons firing in a close-to-irregular fashion at low rates. Using a combination of mean-field and linear response theory we predict the spectra generated in a layered microcircuit model of V1, composed of leaky integrate-and-fire neurons and based on connectivity compiled from anatomical and electrophysiological studies. The model exhibits low- and high-γ oscillations visible in all populations. Since locally generated frequencies are imposed onto other populations, the origin of the oscillations cannot be deduced from the spectra. We develop an universally applicable systematic approach that identifies the anatomical circuits underlying the generation of oscillations in a given network. Based on a theoretical reduction of the dynamics, we derive a sensitivity measure resulting in a frequency-dependent connectivity map that reveals connections crucial for the peak amplitude and frequency of the observed oscillations and identifies the minimal circuit generating a given frequency. The low-γ peak turns out to be generated in a sub-circuit located in layer 2/3 and 4, while the high-γ peak emerges from the inter-neurons in layer 4. Connections within and onto layer 5 are found to regulate slow rate fluctuations. We further demonstrate how small perturbations of the crucial connections have significant impact on the population spectra, while the impairment of other connections leaves the dynamics on the population level unaltered. The study uncovers connections where mechanisms controlling the spectra of the cortical microcircuit are most effective.
Contributors: João Casaleiro, Luís B. Oliveira, Igor M. Filanovsky
oscillation frequency and the coupling strength. ...frequency, phase error and amplitude mismatch that are validated by simulations...RC-oscillator with capacitive coupling fabricated in 130nm CMOS circuit...RC-oscillators...RC-oscillators is investigated. The capacitive coupling has the advantages...Frequency of oscillation with the oscillators uncoupled and coupled (CX...RC-oscillators with the same circuit topology. ...RC-oscillators. ...RC-oscillators, yet the dissipated power is about four times less. We ...frequency. ...oscillator...oscillators ... In this paper the capacitive coupling in quadrature RC-oscillators is investigated. The capacitive coupling has the advantages of being noiseless with a small area penalty and without increasing the power dissipation. The results show that a phase error below 1° and an amplitude mismatch lower than 1% are obtained with a coupling capacitance about 20% of the oscillator׳s capacitance value. Due to this kind of coupling, the phase-noise improves by 3dB (to −115.1 dBc/Hz @ 10MHz) and the increase of power requirement is only marginal leading to a figure-of-merit of −154.8dBc/Hz. This is comparable to the best state-of-the-art RC-oscillators, yet the dissipated power is about four times less. We present calculations of frequency, phase error and amplitude mismatch that are validated by simulations. The theory shows that phase error is proportional to the amplitude mismatch, indicating that an automatic phase error minimization based on the amplitude mismatches is possible. The measurements on a 2.4GHz voltage-controlled quadrature RC-oscillator with capacitive coupling fabricated in 130nm CMOS circuit prototypes validate the theory.
Article - Simulation of Spontaneous Ca2+ Oscillations in Astrocytes Mediated by Voltage-Gated Calcium Channels
Contributors: Shuai Zeng, Bing Li, Shaoqun Zeng, Shangbin Chen
frequency-encoded in signaling. Moreover, the properties of Ca2+ oscillations...oscillation. Within −70.0 to −64.9 mV, the frequency and amplitude of ...oscillations in astrocytes....oscillations in silico. Our model could mimic the oscillatory phenomenon...oscillations of astrocytes. By incorporating different types of voltage-gated...frequency (dotted line) decreased with temperature. ...frequency of Ca2+ oscillations increased with a rise in extracellular ...Frequency of Ca2+ oscillations versus membrane potential. ...oscillations changed slightly (both frequency changed...frequency of Ca2+ oscillations versus temperature. In the temperature ... The purpose of this computational study was to investigate the possible role of voltage-gated Ca2+ channels in spontaneous Ca2+ oscillations of astrocytes. By incorporating different types of voltage-gated Ca2+ channels and a previous model, this study reproduced typical Ca2+ oscillations in silico. Our model could mimic the oscillatory phenomenon under a wide range of experimental conditions, including resting membrane potential (−75 to −60 mV), extracellular Ca2+ concentration (0.1 to 1500 μM), temperature (20 to 37°C), and blocking specific Ca2+ channels. By varying the experimental conditions, the amplitude and duration of Ca2+ oscillations changed slightly (both <25%), while the frequency changed significantly (∼400%). This indicates that spontaneous Ca2+ oscillations in astrocytes might be an all-or-none process, which might be frequency-encoded in signaling. Moreover, the properties of Ca2+ oscillations were found to be related to the dynamics of Ca2+ influx, and not only to a constant influx. Therefore, calcium channels dynamics should be used in studying Ca2+ oscillations. This work provides a platform to explore the still unclear mechanism of spontaneous Ca2+ oscillations in astrocytes.
A better oscillation detection method robustly extracts EEG rhythms across brain state changes: The human alpha rhythm as a test case
Contributors: Tara A. Whitten, Adam M. Hughes, Clayton T. Dickson, Jeremy B. Caplan
oscillation detection across frequency, region and task. Here we show ...oscillations at the alpha frequency (9.5Hz) highlighted in red, using ...OSCillation detection) method. This method produces systematic, objective...Oscillations detected across all frequencies by the oscillatory episode...oscillations were detected at each frequency. (E) The raw signal from ...Oscillation...frequencies, brain regions and tasks. It does so by modeling the functional ... Oscillatory activity is a principal mode of operation in the brain. Despite an intense resurgence of interest in the mechanisms and functions of brain rhythms, methods for the detection and analysis of oscillatory activity in neurophysiological recordings are still highly variable across studies. We recently proposed a method for detecting oscillatory activity from time series data, which we call the BOSC (Better OSCillation detection) method. This method produces systematic, objective, and consistent results across frequencies, brain regions and tasks. It does so by modeling the functional form of the background spectrum by fitting the empirically observed spectrum at the recording site. This minimizes bias in oscillation detection across frequency, region and task. Here we show that the method is also robust to dramatic changes in state that are known to influence the shape of the power spectrum, namely, the presence versus absence of the alpha rhythm, and can be applied to independent components, which are thought to reflect underlying sources, in addition to individual raw signals. This suggests that the BOSC method is an effective tool for measuring changes in rhythmic activity in the more common research scenario wherein state is unknown.
Contributors: Tolga Esat Özkurt, Alfons Schnitzler
frequency) and 15Hz (phase frequency). The simulated signal contained ...Cross-frequency coupling...oscillations (at 20, 25, 30, 40 and 100Hz) having no coupling relation...oscillations and noise. ...Oscillations ... Recent studies have observed the ubiquity of phase–amplitude coupling (PAC) phenomenon in human and animal brain recordings. While various methods were performed to quantify it, a rigorous analytical definition of PAC is lacking. This paper yields an analytical definition and accordingly offers theoretical insights into some of the current methods. A direct PAC estimator based on the given definition is presented and shown theoretically to be superior to some of the previous methods such as general linear model (GLM) estimator. It is also shown that the proposed PAC estimator is equivalent to GLM estimator when a constant term is removed from its formulation. The validity of the derivations is demonstrated with simulated data of varying noise levels and local field potentials recorded from the subthalamic nucleus of a Parkinson's disease patient.
Contributors: R. Kalter, M.J. Tummers, S. Kenjereš, B.W. Righolt, C.R. Kleijn
oscillations kosc,2D. The inlet velocity is vin=0.4m/s (Rein=3.1×103, ...oscillations. The low frequency self-sustained jet oscillations induce...oscillations of turbulent jets (Re=3.1×103) issuing from a submerged bifurcated...Frequency peaks are found at fPOD=0.027Hz (FL<0), fPOD=0.046Hz (FL=0) ...frequency peaks are in reasonable agreement with the frequencies found...oscillation. When FLoscillation is...oscillation amplitude is enhanced by a factor of 1.5....frequency fTS of the free surface oscillation at a monitoring point at...frequency fPOD from the power spectrum of the first chrono mode of the...oscillations ... The effect of Lorentz forcing on self-sustained oscillations of turbulent jets (Re=3.1×103) issuing from a submerged bifurcated nozzle into a thin rectangular liquid filled cavity was investigated using free surface visualization and time-resolved particle image velocimetry (PIV). A Lorentz force is produced by applying an electrical current across the width of the cavity in conjunction with a magnetic field. As a working fluid a saline solution is used. The Lorentz force can be directed downward (FL0), to weaken or strengthen the self-sustained jet oscillations. The low frequency self-sustained jet oscillations induce a free surface oscillation. When FL0 the free surface oscillation amplitude is enhanced by a factor of 1.5.
Contributors: Andrada Ianuş, Bernard Siow, Ivana Drobnjak, Hui Zhang, Daniel C. Alexander
oscillation frequency for four different sizes of the restricted compartment...oscillation frequency for (a) several values of Δ, R=5μm and G=0.1T/m;...Oscillating gradient...oscillations. Restricted diffusion as a function of (c) gradient strength...oscillations have been popular for some time, recent work suggests additional...oscillating gradient spin echo (OGSE) sequences using the Gaussian phase...frequencies, R=5μm and Δ=45ms; (d) cylinder radius for several frequencies...oscillating waveforms. This paper presents analytical expressions of the...oscillation frequency and are accurate to within a few percent. Finally...oscillations...oscillation frequency. ...Oscillating gradients provide an optimal probe of small pore sizes in ... Oscillating gradients provide an optimal probe of small pore sizes in diffusion MRI. While sinusoidal oscillations have been popular for some time, recent work suggests additional benefits of square or trapezoidal oscillating waveforms. This paper presents analytical expressions of the free and restricted diffusion signal for trapezoidal and square oscillating gradient spin echo (OGSE) sequences using the Gaussian phase distribution (GPD) approximation and generalises existing similar expressions for sinusoidal OGSE. Accurate analytical models are necessary for exploitation of these pulse sequences in imaging studies, as they allow model fitting and parameter estimation in reasonable computation times. We evaluate the accuracy of the approximation against synthesised data from the Monte Carlo (MC) diffusion simulator in Camino and Callaghan’s matrix method and we show that the accuracy of the approximation is within a few percent of the signal, while providing several orders of magnitude faster computation. Moreover, since the expressions for trapezoidal wave are complex, we test sine and square wave approximations to the trapezoidal OGSE signal. The best approximations depend on the gradient amplitude and the oscillation frequency and are accurate to within a few percent. Finally, we explore broader applications of trapezoidal OGSE, in particular for non-model based applications, such as apparent diffusion coefficient estimation, where only sinusoidal waveforms have been considered previously. We show that with the right apodisation, trapezoidal waves also have benefits by virtue of the higher diffusion weighting they provide compared to sinusoidal gradients.
Contributors: N. Mykytenko, D. Fink, A. Kiv
oscillations on the frequency of FR. (b) Dependence of the average spike...oscillations in real track structure. The model describes adequately the...oscillations of model particles is proportional to the average amplitude...oscillation effect in the track structure: oscillations of the model particles...frequency of applied voltage; Points: measurements, the curve is drown...oscillations (b). ...oscillating model particles located in the nodes of a plane lattice. In...frequency of FR. ... A phenomenological model for description of ion current pulsations in track-containing foils is proposed. Such structures belong to artificial porous materials having diverse applications. Typically pulsations of the ion current are observed in experiments in which the track-containing polymer foils are embedded in electrolytes, and AC voltage is applied. The proposed model is designed on the base of classical molecular dynamics. The interacting currents in tracks are simulated by two-dimensional system of oscillating model particles located in the nodes of a plane lattice. In the model external discontinuous forces are introduced to simulate an application of AC voltage. Interaction between model particles is varied to clarify its influence on pulsation effect. It is assumed that the average amplitude of oscillations of model particles is proportional to the average amplitude of current oscillations in real track structure. The model describes adequately the main features of the pulsation effect that were found experimentally. The obtained results can be useful for creation and improvement of sensors and other devices of track electronics.