Slow Modulation Research Articles

Harmonics-to-noise ratio estimation with deterministically time-varying harmonic model for pathological voice signals.

The harmonics-to-noise ratio (HNR) and other spectral noise parameters are important in clinical objective voice assessment as they could indicate the presence of nonharmonic phenomena, which are tied to the perception of hoarseness or breathiness. Existing HNR estimators are built on the voice signals to be nearly periodic (fixed over a short period), although voice pathology could induce involuntary slow modulation to void this assumption. This paper proposes the use of a deterministically time-varying harmonic model to improve the HNR measurements. To estimate the time-varying model, a two-stage iterative least squares algorithm is proposed to reduce model overfitting. The efficacy of the proposed HNR estimator is demonstrated with synthetic signals, simulated tremor signals, and recorded acoustic signals. Results indicate that the proposed algorithm can produce consistent HNR measures as the extent and rate of tremor are varied.

Three-dimensional memristive Morris-Lecar model with magnetic induction effects and its FPGA implementation.

To characterize the magnetic induction flow induced by neuron membrane potential, a three-dimensional (3D) memristive Morris-Lecar (ML) neuron model is proposed in this paper. It is achieved using a memristor induction current to replace the slow modulation current in the existing 3D ML neuron model with fast-slow structure. The magnetic induction effects on firing activities are explained by the spiking/bursting firings with period-adding bifurcation and periodic/chaotic spiking-bursting patterns, and the bifurcation mechanisms of the bursting patterns are elaborated using the fast-slow analysis method to create two bifurcation sets. In particular, the 3D memristive ML model can also exhibit the homogeneous coexisting bursting patterns when switching the memristor initial states, which are effectively illustrated by the theoretical analysis and numerical simulations. Finally, a digitally FPGA-based hardware platform is developed for the 3D memristive ML model and the experimentally measured results well verify the numerical ones.

Perturbing period-one laser dynamics for frequency-modulated microwave generation with external locking.

Period-one (P1) dynamics of two lasers under a common injection are perturbed for externally locked frequency-modulated continuous-wave (FMCW) generation. The first laser is injected into P1 dynamics at frequency f 0, where the dynamics is perturbed by a slow modulation to induce adiabatic sweeping for FMCW generation and a fast modulation to seed the whole comb for external locking. The second laser is injected into a faster P1 dynamics at 3f 0 that is perturbed for harmonic locking. The central frequency is boosted to 4f 0 by coherently combining the lasers. FMCW generation with external locking is demonstrated with a sweep range of 6 GHz, comb contrast enhanced to 42 dB, and 4f 0 reaching 80 GHz. Inherent competition between external locking and frequency modulation is revealed, although an optimal strength is identified for locking the whole comb. Wide tuning of the central frequency is also supported.

Detecting slow narrowband modulation in EEG signals

BackgroundWe observed an unusual modulatory phenomenon in the electroencephalogram (EEG) of pediatric patients with acquired brain injury. The modulation is orders of magnitude slower than the fast EEG background activity, necessitating new analysis procedures to systematically detect and quantify the phenomenon. New methodWe propose a method for analyzing spatial and temporal relationships associated with slow, narrowband modulation of EEG. We extract envelope signals from physiological frequency bands of EEG. Then, we construct a sparse representation of the spectral content of the envelope signal across sliding windows. For the latter, we use an augmented LASSO regression to incorporate spatial and temporal filtering into the solution. The method can be applied to windows of variable length, depending on the desired frequency resolution. ResultsThe sparse estimates of the envelope power spectra enable the detection of narrowband modulation in the millihertz frequency range. Subsequently, we are able to assess non-stationarity in the frequency and spatial relationships across channels. The method can be paired with unsupervised anomaly detection to identify windows with significant modulation. We validated such findings by applying our method to a control set of EEGs. Comparison with existing methodsTo our knowledge, no methods have been previously proposed to quantify second order modulation at such disparate time-scales. ConclusionsWe provide a general EEG analysis framework capable of detecting signal content below 0.1 Hz, which is especially germane to clinical recordings that may contain multiple hours worth of continuous data.

Unravelling neuron-astrocyte communication in the dorsal raphe nucleus.

Introduction: Serotonin is a neuromodulator widely spread throughout the central nervous system and involved in a vast variety of behaviors, such as cognitive functions and emotional states. On this basis, serotonergic dysfunction has been related to several psychiatric disorders such as Major Depressive Disorder, schizophrenia, or autism. Despite serotonin’s widespread distribution, the location of serotonergic neurons is restricted to the midbrain raphe nuclei. In this context, astrocytes are known to participate in synaptic transmission modulating neural circuits; however, their role in the serotonergic system remains largely unknown. My study aims to elucidate the neuron-astrocyte signaling at serotonergic nuclei, looking at the dorsal raphe nucleus (DRN). Materials and methods: For the purpose of this project, we performed intracranial injections of viral constructs in adult mice to express the Ca2+ indicator GCaMP6 specifically in DRN astrocytes, Ca2+ imaging experiments to record astrocytic activity, electrophysiological recordings of neuronal activity using patch-clamp and immunohistochemistry techniques. Results and conclusions: Preliminary data show that astrocytes from DRN respond to serotonin with an increase in the amplitude and frequency of intracellular Ca2+ events, which is partly mediated by serotonin type 2 receptors. As a consequence of triggering Ca2+ signaling, we found that serotonin induces gliotransmission, shown by an increased frequency of Slow Inward Currents (SICs) and modulation of excitatory synaptic transmission in dorsal raphe neurons. In conclusion, these data suggest that astrocytes might play a role in synaptic transmission and neuronal excitability in the DRN and, therefore, in the serotonergic-mediated actions of DRN.

Hanle rotation signatures in Sr I 4607 Å

Context. Measuring small-scale magnetic fields and constraining their role in energy transport and dynamics in the solar atmosphere are crucial, albeit challenging, tasks in solar physics. To this aim, observations of scattering polarization and the Hanle effect in various spectral lines are increasingly used to complement traditional magnetic field determination techniques. Aims. One of the strongest scattering polarization signals in the photosphere is measured in the Sr I line at 4607.3 Å when observed close to the solar limb. Here, we present the first observational evidence of Hanle rotation in the linearly polarized spectrum of this line at several limb distances. Methods. We used the Zurich IMaging POLarimeter, ZIMPOL at the IRSOL observatory, with exceptionally good seeing conditions and long integration times. We combined the fast-modulating polarimeter with a slow modulator installed in front of the telescope. This combination allows for a high level of precision and unprecedented accuracy in the measurement of spectropolarimetric data. Results. Fixing the reference direction for positive Stokes Q parallel to the limb, we detected singly peaked U/I signals well above the noise level. We can exclude any instrumental origins for such U/I signals. These signatures are exclusively found in the Sr I line, but not in the adjoining Fe I line, therefore eliminating the Zeeman effect as the mechanism responsible for their appearance. However, we find a clear spatial correlation between the circular polarization produced by the Zeeman effect and the U/I amplitudes. This suggests that the detected U/I signals are the signatures of Hanle rotation caused by a spatially resolved magnetic field. Conclusions. A novel measurement technique allows for determining the absolute level of polarization with unprecedented precision. Using this technique, high-precision spectropolarimetric observations reveal, for the first time, unambiguous U/I signals attributed to Hanle rotation in the Sr I line.

Response behavior of bi-stable point wave energy absorbers under harmonic wave excitations

To expand the narrow response bandwidth of linear point wave energy absorbers (PWAs), a few research studies have recently proposed incorporating a bi-stable restoring force in the design of the absorber. Such studies have relied on numerical simulations to demonstrate the improved bandwidth of the bi-stable absorbers. In this work, we aim to understand how the shape of the bi-stable restoring force influences the effective bandwidth of the absorber. To this end, we use perturbation methods to obtain an approximate analytical solution of the nonlinear differential equations governing the complex motion of the absorber under harmonic wave excitations. The approximate solution is validated against a numerical solution obtained via direct integration of the equations of motion. Using a local stability analysis of the equations governing the slow modulation of the amplitude and phase of the response, the loci of the different bifurcation points are determined as function of the wave frequency and amplitude. Those bifurcation points are then used to define an effective bandwidth of the absorber. The influence of the shape of the restoring force on the effective bandwidth is also characterized by generating design maps that can be used to predict the kind of response behavior (small amplitude periodic, large amplitude periodic, or aperiodic) for any given combination of wave amplitude and frequency. Such maps are critical toward designing efficient bi-stable PWAs for known wave conditions.

Distinct neuronal types contribute to hybrid temporal encoding strategies in primate auditory cortex.

Studies of the encoding of sensory stimuli by the brain often consider recorded neurons as a pool of identical units. Here, we report divergence in stimulus-encoding properties between subpopulations of cortical neurons that are classified based on spike timing and waveform features. Neurons in auditory cortex of the awake marmoset (Callithrix jacchus) encode temporal information with either stimulus-synchronized or nonsynchronized responses. When we classified single-unit recordings using either a criteria-based or an unsupervised classification method into regular-spiking, fast-spiking, and bursting units, a subset of intrinsically bursting neurons formed the most highly synchronized group, with strong phase-locking to sinusoidal amplitude modulation (SAM) that extended well above 20 Hz. In contrast with other unit types, these bursting neurons fired primarily on the rising phase of SAM or the onset of unmodulated stimuli, and preferred rapid stimulus onset rates. Such differentiating behavior has been previously reported in bursting neuron models and may reflect specializations for detection of acoustic edges. These units responded to natural stimuli (vocalizations) with brief and precise spiking at particular time points that could be decoded with high temporal stringency. Regular-spiking units better reflected the shape of slow modulations and responded more selectively to vocalizations with overall firing rate increases. Population decoding using time-binned neural activity found that decoding behavior differed substantially between regular-spiking and bursting units. A relatively small pool of bursting units was sufficient to identify the stimulus with high accuracy in a manner that relied on the temporal pattern of responses. These unit type differences may contribute to parallel and complementary neural codes.

Slow and fast adaptive modulation and coding for uplink massive MIMO systems with packet retransmission

Here, the authors consider the uplink of a cellular massive multiple-input multiple-output (MIMO) system with maximum ratio combiner (MRC) at base stations (BSs). To achieve a better QoS provisioning, users in the cells employ link adaptation using adaptive modulation and coding (AMC) in conjunction with packet retransmission. The authors present a cross-layer approach for the AMC design exploiting the time variation feature of MIMO wireless channels. At first, a fast AMC (FAMC) scheme is proposed to adapt the fast small-scale fading of the wireless channel based on the instantaneous channel state information. Since the fast fading is asymptotically averaged out due to the channel hardening property of massive MIMO system, we then suggest a slow AMC (SAMC) scheme which adjusts the adaptation parameters based on only the large-scale channel fading statistics including shadow fading and pass loss of the channel. The SAMC substantially reduces the feedback rate and implementation cost because of using a larger coherence time compared to that of the FAMC. For the proposed schemes, the probability density function of signal-to-interference-plus-noise ratio (SINR) for MRC receivers at BSs is analytically derived and verified by simulation. Also, closed-form expressions are presented for the throughput and packet error outage of the system. Index Terms—Massive MIMO, MRC, AMC, ARQ, Performance analysis.

Cone-Driven Retinal Responses Are Shaped by Rod But Not Cone HCN1.

Signal integration of converging neural circuits is poorly understood. One example is in the retina where the integration of rod and cone signaling is responsible for the large dynamic range of vision. The relative contribution of rods versus cones is dictated by a complex function involving background light intensity and stimulus temporal frequency. One understudied mechanism involved in coordinating rod and cone signaling onto the shared retinal circuit is the hyperpolarization activated current (Ih) mediated by hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels expressed in rods and cones. Ih opposes membrane hyperpolarization driven by activation of the phototransduction cascade and modulates the strength and kinetics of the photoreceptor voltage response. We examined conditional knock-out (KO) of HCN1 from mouse rods using electroretinography (ERG). In the absence of HCN1, rod responses are prolonged in dim light which altered the response to slow modulation of light intensity both at the level of retinal signaling and behavior. Under brighter intensities, cone-driven signaling was suppressed. To our surprise, conditional KO of HCN1 from mouse cones had no effect on cone-mediated signaling. We propose that Ih is dispensable in cones because of the high level of temporal control of cone phototransduction. Thus, HCN1 is required for cone-driven retinal signaling only indirectly by modulating the voltage response of rods to limit their output.SIGNIFICANCE STATEMENT Hyperpolarization gated hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels carry a feedback current that helps to reset light-activated photoreceptors. Using conditional HCN1 knock-out (KO) mice we show that ablating HCN1 from rods allows rods to signal in bright light when they are normally shut down. Instead of enhancing vision this results in suppressing cone signaling. Conversely, ablating HCN1 from cones was of no consequence. This work provides novel insights into the integration of rod and cone signaling in the retina and challenges our assumptions about the role of HCN1 in cones.

Dynamic Behaviour of Donor Specific Antibodies in the Early Period Following HLA Incompatible Kidney Transplantation.

In HLA-incompatible kidney transplantation, monitoring donor-specific antibodies (DSA) plays a crucial role in providing appropriate treatment and increases kidney survival times. This work aimed to determine if early post-transplant DSA dynamics inform graft outcome over and above other predictive factors. Eighty-eight cases were classified by unsupervised machine learning into five distinct DSA response groups: no response, fast modulation, slow modulation, rise to sustained and sustained. Fast modulation dynamics gave an 80% rate for early acute rejection, whereas the sustained group was associated with the lowest rejection rates (19%). In complete contrast, the five-year graft failure was lowest in the modulation groups (4–7%) and highest in the sustained groups (25–31%). Multivariable analysis showed that a higher pre-treatment DSA level, male gender and absence of early acute rejection were strongly associated with a sustained DSA response. The modulation group had excellent five-year outcomes despite higher rates of early rejection episodes. This work further develops an understanding of post-transplant DSA dynamics and their influence on graft survival following HLA-incompatible kidney transplantation.

Dynamics of temporally modulated materials: Adiabatic transformations and frequency conversion

The recent progress in the context of elastic metamaterials and modulated waveguides with digitally controllable properties has spurred the research in the context of time-varying and space-time varying mechanical systems. In other words, the search of new functionalities, such as nonreciprocity, frequency conversion, parametric amplification, and edge-to-edge pumping, to name a few, requires advanced space-time control of the material parameters, which justifies the emergence of active times in phononics. The work presented herein discusses temporal modulations in the context of stiffness-modulated elastic structures, with emphasis on frequency conversion and wave steering. It is shown that slow temporal modulations, compliant with the adiabatic theorem, can be functionally employed to change the frequency content and the propagation direction of incident wave packets. At the same time, adiabatic variations avoid the scattering of back-propagating waves, which are instead present in case of fast modulations and, in many cases, can be undesired from a practical perspective. Both transient and steady-state behaviors of stiffness-modulated waveguides are discussed with the goal of achieving controllable transmission of elastic signals between an emitter and a receiver.

An Energy-Efficient Power Allocation Scheme for NOMA-Based IoT Sensor Networks in 6G

Non-orthogonal multiple access (NOMA) is an upcoming technique to boost the capacity of visible light communication (VLC) systems which is otherwise limited by the slow modulation response of light-emitting diode (LED) sources used therein. We propose to enhance the energy efficiency of NOMA-based VLC systems, thereby making them suitable for green Internet of things (IoT) in the sixth generation (6G) networks. The proposed energy-efficient power allocation (EPA) scheme reduces the average bit error rate (ABER) and augments the system’s energy efficiency as well as its capacity and fairness. However, at high values of transmitted power, there is a trade-off between energy efficiency and ABER. We define and evaluate the energy utilization factor to study this trade-off and show that the EPA scheme has superior energy utilization than the state-of-the-art power allocation schemes. Moreover, its performance does not deteriorate appreciably when the number of connected users (or sensor nodes) is increased. Based on numerical and simulation results, we deduce that the proposed EPA scheme meets the requirements of green IoT systems in 6G networks.

Better speech-in-noise comprehension is associated with enhanced neural speech tracking in older adults with hearing impairment

The alignment between low-frequency activity in the brain and slow acoustic modulations in the speech signal depicts a core principle in present theories of speech perception—a process referred to as ‘neural speech tracking’. While most older adults, particularly those with highly prevalent age-related hearing loss, have difficulties with speech perception and comprehension, the impact of hearing loss on neural speech tracking is still unclear. In this study we investigated the effects of pure-tone hearing loss and different types of background noise on the neural tracking response in a large sample of older adults (N = 101). Furthermore, we examined whether the neural tracking response was predictive for speech comprehension. For this purpose, we obtained scalp EEG from our participants who had varying degrees of pure-tone hearing loss (7.5–59.6 dB HL for .5–8 kHz pure tones) while they listened to sentences in quiet, pink and multi-talker babble noise. Speech tracking was quantified by computing the cross-correlation between the EEG signal and the amplitude envelope of the sentences heard. A higher degree of pure-tone hearing loss was associated with greater neural speech tracking (i.e., greater cross-correlation). Additionally, neural speech tracking showed a positive association with speech comprehension. This relationship was modulated by the degree of pure-tone hearing loss with hearing-impaired participants benefitting more from greater neural speech tracking. Our results highlight the potential of neural speech tracking as an objective measure of speech comprehension and as a possible target mechanism for clinical interventions such as neurofeedback. Furthermore, the interaction between speech tracking and pure-tone hearing loss suggests a compensatory mechanism by which the hearing-impaired rely more on slow amplitude modulations in the speech signal.

Slow phase-locked modulations support selective attention to sound

To make sense of complex soundscapes, listeners must select and attend to task-relevant streams while ignoring uninformative sounds. One possible neural mechanism underlying this process is alignment of endogenous oscillations with the temporal structure of the target sound stream. Such a mechanism has been suggested to mediate attentional modulation of neural phase-locking to the rhythms of attended sounds. However, such modulations are compatible with an alternate framework, where attention acts as a filter that enhances exogenously-driven neural auditory responses. Here we attempted to test several predictions arising from the oscillatory account by playing two tone streams varying across conditions in tone duration and presentation rate; participants attended to one stream or listened passively. Attentional modulation of the evoked waveform was roughly sinusoidal and scaled with rate, while the passive response did not. However, there was only limited evidence for continuation of modulations through the silence between sequences. These results suggest that attentionally-driven changes in phase alignment reflect synchronization of slow endogenous activity with the temporal structure of attended stimuli.

Entangled two-photon absorption with Brownian-oscillator fluctuations.

We theoretically investigate the two-photon absorption signals of a three-band (g, e, f) system diagonally coupled to an over-damped Brownian oscillator bath, which induces random Gaussian modulations of energy levels with an arbitrary degree of correlation. For fast modulation, extra 2ωeg and 2ωfe peaks may obscure the g-f transitions in the classical two-photon absorption (CTPA) spectra for nearly resonant e states. These peaks arise from one-photon resonant g-e or e-f transitions. In the slow modulation limit, these peaks vanish because of the short tails of the Gaussian line shape. CTPA strongly depends on the correlations between energy fluctuations. In entangled two-photon absorption, the extra peaks are eliminated because of the broad one-photon but narrow two-photon spectrum of the twin photons. The variation of the coherences between f states with the correlation between energy fluctuations is explored.

Output characteristic of four-frequency Zeeman laser gyroscope with an alternating frequency bias

We have experimentally studied the output characteristic of a four-frequency Zeeman laser gyroscope (ZLG) on longitudinal modes with orthogonal circular polarisations having an alternating frequency bias and compared it with the output characteristic of a two-frequency ZLG. It is shown that by representing a four-frequency ZLG as a set of two-frequency ZLGs with orthogonal polarisations, the output characteristic of a four-frequency ZLG can be obtained through the arithmetic mean of the output characteristics of the same gyroscope. The experimental output characteristic of a four-frequency ZLG with an alternating bias in the form of a meander with a switching frequency of 1 kHz, as well as its combination with a low-frequency meander with a frequency of 1 Hz, is presented. The efficiency of using slow meander modulation for the linearization of the output characteristic of a four-frequency ZLG is demonstrated.

Quantifying the Kinetics of Signaling and Arrestin Recruitment by Nervous System G-Protein Coupled Receptors.

Neurons integrate inputs over different time and space scales. Fast excitatory synapses at boutons (ms and μm), and slow modulation over entire dendritic arbors (seconds and mm) are all ultimately combined to produce behavior. Understanding the timing of signaling events mediated by G-protein-coupled receptors is necessary to elucidate the mechanism of action of therapeutics targeting the nervous system. Measuring signaling kinetics in live cells has been transformed by the adoption of fluorescent biosensors and dyes that convert biological signals into optical signals that are conveniently recorded by microscopic imaging or by fluorescence plate readers. Quantifying the timing of signaling has now become routine with the application of equations in familiar curve fitting software to estimate the rates of signaling from the waveform. Here we describe examples of the application of these methods, including (1) Kinetic analysis of opioid signaling dynamics and partial agonism measured using cAMP and arrestin biosensors; (2) Quantifying the signaling activity of illicit synthetic cannabinoid receptor agonists measured using a fluorescent membrane potential dye; (3) Demonstration of multiplicity of arrestin functions from analysis of biosensor waveforms and quantification of the rates of these processes. These examples show how temporal analysis provides additional dimensions to enhance the understanding of GPCR signaling and therapeutic mechanisms in the nervous system.

Neurovascular disease: 2022 update.

In this update we present a series of papers focused on topics that have emerged in vascular disease over the prior year. The first two papers focus on the pathogenesis of vascular malformations, the first on brain arteriovenous malformations, and the second on cerebral cavernous malformations. These disorders can lead to significant brain injuries from intracerebral hemorrhage (if they rupture) or other neurological complications, including seizures. The next set of papers reflects work that has advanced our understanding of how the brain and the immune system "communicate" after brain injury, including stroke (papers 3-6). The first of these shows that T cells are involved in white matter repair after ischemic injury, an effect dependent on microglia, demonstrating the important cross-talk between innate and adaptive immunity. The next two papers focus on B cells, which have been relatively understudied in the context of brain injury. The contribution of antigen-experienced B cells from the meninges and skull bone marrow, rather than blood-derived B cells in neuroinflammation opens up a very novel area of investigation. The possibility that antibody secreting B cells may contribute to vascular dementia will certainly be an active area for future investigations. Similarly, in paper 6, investigators found that CNS-infiltrating myeloid cells can originate from brain borders tissues. These cells have unique transcriptional signatures that are distinct from their blood-derived counterparts, and likely contribute to myeloid cell infiltration from bone-marrow niches in close proximity to the brain. The contribution of microglia, the primary innate immune cell of the brain, to amyloid deposition and propagation is then discussed, followed by work on how perivascular Aβ is potentially cleared along the cerebral vessels in patients with cerebral amyloid angiopathy. The final two papers focus on the contribution of senescent endothelial cells and pericytes. The first used a model of accelerated senescence (Hutchinson-Gilford progeria syndrome; HGPS) and shows the translational potential of an approach to reduce telomere shortening to slow aging. The final paper demonstrates how capillary pericytes contribute to basal blood flow resistance and slow modulation of blood flow throughout the brain. Interestingly, several of the papers identified therapeutic strategies that could be potentially translated into clinical populations.

Interaural-time-difference thresholds for broad band-limited pulses are affected by relative bandwidth not temporal envelope sharpness.

Humans are sensitive to interaural time differences (ITDs) conveyed by slow modulations on high-frequency carrier signals. Sensitivity appears to be affected by temporal envelope sharpness, but it is unclear if there is a limit to which sharpness affects sensitivity. Pulse trains were varied in relative bandwidth (re: critical bandwidths) and center frequency. ITD sensitivity increased with increasing bandwidth. There was no effect of center frequency when relative bandwidths were analyzed, suggesting that the temporal envelope sharpness (concomitantly absolute bandwidth in Hz) did not affect performance. Rather, sensitivity was most easily explained by recruitment of additional auditory channels.