High Frequency Oscillations Research Articles

Profiling the low-beta characteristics of the subthalamic nucleus in early- and late-onset Parkinson's disease.

Low-beta oscillation (13-20 Hz) has rarely been studied in patients with early-onset Parkinson's disease (EOPD, age of onset ≤50 years). We aimed to explore the characteristics of low-beta oscillation in the subthalamic nucleus (STN) of patients with EOPD and investigate the differences between EOPD and late-onset Parkinson's disease (LOPD). We enrolled 31 EOPD and 31 LOPD patients, who were matched using propensity score matching. Patients underwent bilateral STN deep brain stimulation (DBS). Local field potentials were recorded using intraoperative microelectrode recording. We analyzed the low-beta band parameters, including aperiodic/periodic components, beta burst, and phase-amplitude coupling. We compared low-beta band activity between EOPD and LOPD. Correlation analyses were performed between the low-beta parameters and clinical assessment results for each group. We found that the EOPD group had lower aperiodic parameters, including offset (p = 0.010) and exponent (p = 0.047). Low-beta burst analysis showed that EOPD patients had significantly higher average burst amplitude (p = 0.016) and longer average burst duration (p = 0.011). Furthermore, EOPD had higher proportion of long burst (500-650 ms, p = 0.008), while LOPD had higher proportion of short burst (200-350 ms, p = 0.007). There was a significant difference in phase-amplitude coupling values between low-beta phase and fast high frequency oscillation (300-460 Hz) amplitude (p = 0.019). We found that low-beta activity in the STN of patients with EOPD had characteristics that varied when compared with LOPD, and provided electrophysiological evidence for different pathological mechanisms between the two types of PD. These differences need to be considered when applying adaptive DBS on patients of different ages.

Interregional phase-amplitude coupling between theta rhythm in the nucleus tractus solitarius and high-frequency oscillations in the hippocampus during REM sleep in rats.

Cross-frequency coupling (CFC) between theta and high-frequency oscillations (HFOs) is predominant during active wakefulness, REM sleep and behavioral and learning tasks in rodent hippocampus. Evidence suggests that these state-dependent CFCs are linked to spatial navigation and memory consolidation processes. CFC studies currently include only the cortical and subcortical structures. To our knowledge, the study of nucleus tractus solitarius (NTS)-cortical structure CFC is still lacking. Here we investigate CFC in simultaneous local field potential recordings from hippocampal CA1 and the NTS during behavioral states in freely moving rats. We found a significant increase in theta (6-8 Hz)-HFO (120-160 Hz) coupling both within the hippocampus and between NTS theta and hippocampal HFOs during REM sleep. Also, the hippocampal HFOs were modulated by different but consistent phases of hippocampal and NTS theta oscillations. These findings support the idea that phase-amplitude coupling is both state- and frequency-specific and CFC analysis may serve as a tool to help understand the selective functions of neuronal network interactions in state-dependent information processing. Importantly, the increased NTS theta-hippocampal HFO coupling during REM sleep may represent the functional connectivity between these two structures which reflects the function of the hippocampus in visceral learning with the sensory information provided by the NTS. This gives a possible insight into an association between the sensory activity and REM-sleep dependent memory consolidation.

Face pareidolia is enhanced by 40 Hz transcranial alternating current stimulation (tACS) of the face perception network

Pareidolia refers to the perception of ambiguous sensory patterns as carrying a specific meaning. In its most common form, pareidolia involves human-like facial features, where random objects or patterns are illusionary recognized as faces. The current study investigated the neurophysiological correlates of face pareidolia via transcranial alternating current stimulation (tACS). tACS was delivered at gamma (40 Hz) frequency over critical nodes of the “face perception” network (i.e., right lateral occipito-temporal and left prefrontal cortex) of 75 healthy participants while completing four face perception tasks (‘Mooney test’ for faces, ‘Toast test’, ‘Noise pareidolia test’, ‘Pareidolia task’) and an object perception task (‘Mooney test’ for objects). In this single-blind, sham-controlled between-subjects study, participants received 35 min of either Sham, Online, (40Hz-tACS_ON), or Offline (40Hz-tACS_PRE) stimulation. Results showed that face pareidolia was causally enhanced by 40Hz-tACS_PRE in the Mooney test for faces in which, as compared to sham, participants more often misperceived scrambled stimuli as faces. In addition, as compared to sham, participants receiving 40Hz-tACS_PRE showed similar reaction times (RTs) when perceiving illusory faces and correctly recognizing noise stimuli in the Toast test, thus not exhibiting hesitancy in identifying faces where there were none. Also, 40Hz-tACS_ON induced slower rejections of face pareidolia responses in the Noise pareidolia test. The current study indicates that 40 Hz tACS can enhance pareidolic illusions in healthy individuals and, thus, that high frequency (i.e., gamma band) oscillations are critical in forming coherent and meaningful visual perception.

Prefrontal cortex neurons in adult rats exposed to early life stress fail to appropriately signal the consequences of motivated actions

Early life stress (ELS) can set the stage for susceptibility to cognitive and emotional dysfunction in adulthood by disrupting typical neural development. The prefrontal cortex (PFC) continues to mature during early life, making this region particularly vulnerable to disruption for animals who experience ELS. Despite this, the effects of ELS experience on in vivo PFC function in awake and behaving adult animals are currently poorly understood. To assess this, we employed an instrumental conflict task to assess how hungry adult rats, either ELS (wet bedding) or unstressed Controls, were able to flexibly alter their motivation for food reward seeking (lever presses) in situations that were either threatening or safe. During this task, in vivo electrophysiological recordings (both single unit and local field potentials [LFPs]) were made in the rats’ ventral-medial PFC (vmPFC). We found that ELS rats were less motivated to lever press for rewards than Controls in the threat situations during repeated extinction sessions. In recordings taken during this suppression task, Control vmPFC neurons displayed reliable differences between motivated actions, such as between rewarded and unrewarded presses, but ELS neurons failed to differentiate these action-outcome differences. We also found differences in task-related LFP activity between groups; in particular, prior ELS experience appears to induce abnormal changes in low-frequency oscillations during shock-associated threat stimuli prior to presses, as well as diminished higher-frequency oscillations following rewarded presses. Collectively, we demonstrate that ELS experience produces persistent impairment in motivational regulation that is associated with significant changes in in vivo PFC signals. Specifically, ELS-experienced adults fail to appropriately update motivated action strategies under threat conditions, and likewise fail to appropriately monitor and update action/outcome relationships in motivated behavior. These ELS-related changes may therefore lay the foundation for heightened susceptibility to mental-health disorders in adults such as substance abuse and post-traumatic stress disorder.

Interictal HFO and FDG-PET correlation predicts surgical outcome following SEEG.

This study aimed to investigate the quantitative relationship between interictal 18 F-fluorodeoxyglucose-positron emission tomography (FDG-PET) and interictal high-frequency oscillations (HFOs) from stereo-electroencephalography (SEEG) recordings in patients with refractory epilepsy. We retrospectively included 32 patients. FDG-PET data were quantified through statistical parametric mapping (SPM) t test modeling with normal controls. Interictal SEEG segments with four, 10-min segments were selected randomly. HFO detection and classification procedures were automatically performed. Channel-based HFOs separating ripple (80-250 Hz) and fast ripple (FR; 250-500 Hz) counts were correlated with the surrounding metabolism T score at the individual and group level, respectively. The association was further validated across anatomic seizure origins and sleep vs wake states. We built a joint feature FR × T reflecting the FR and hypometabolism concordance to predict surgical outcomes in 28 patients who underwent surgery. We found a negative correlation between interictal FDG-PET and HFOs through the linear mixed-effects model (R2 =.346 and .457 for ripples and FRs, respectively, p < .001); these correlations were generalizable to different epileptogenic-zone lobar localizations and vigilance states. The FR × T inside the resection volume could be used as a predictor for surgical outcomes with an area under the curve of 0.81. The degree of hypometabolism is associated with HFO generation rate, especially for FRs. This relationship would be meaningful for selection of SEEG candidates and for optimizing SEEG scheme planning. The concordance between FRs and hypometabolism inside the resection volume could provide prognostic information regarding surgical outcome.

Impact of opacity effects on chromospheric oscillations inferred from NLTE inversions

Context. Spectropolarimetric inversions are a fundamental tool for diagnosing the solar atmosphere. Chromospheric inferences rely on the interpretation of spectral lines that are formed under nonlocal thermodynamic equilibrium (NLTE) conditions. In the presence of oscillations, changes in the opacity impact the response height of the spectral lines and hinder the determination of the real properties of the fluctuations. Aims. We aim to explore the relationship between the chromospheric oscillations inferred by NLTE inversion codes and the intrinsic fluctuations in velocity and temperature produced by the waves. Methods. We computed numerical simulations of wave propagation in a sunspot umbra with the code MANCHA. We used the NLTE synthesis and inversion code NICOLE to compute spectropolarimetric Ca II 8542 Å line profiles for the atmospheric models obtained as the output from the simulations. We then inverted the synthetic profiles and compared the inferences from the inversions with the known atmospheres from the simulations. Results. NLTE inversions of the Ca II 8542 Å line capture low-frequency oscillations, including those in the main band of chromospheric oscillations around 6 mHz. In contrast, waves with frequencies above 9 mHz are poorly characterized by the inversion results. Velocity oscillations at those higher frequencies exhibit clear signs of opacity fluctuations; namely the power of the signal at constant optical depth greatly departs from the power of the oscillations at constant geometrical height. The main response of the line to velocity fluctuations comes from low chromospheric heights, whereas the response to temperature shows sudden jumps between the high photosphere and the low chromosphere. This strong variation in the height where the line is sensitive to temperature is revealed as a strong oscillatory power in the inferred fluctuations, which is much stronger than the actual power from the intrinsic temperature oscillations. Conclusions. Our results validate the use of NLTE inversions to study chromospheric oscillations with frequencies below ∼9 mHz. However, the interpretation of higher-frequency oscillations and the power of temperature oscillations must be addressed with care, as these exhibit signatures of opacity oscillations.

Dynamics of axially moving beams: A finite difference approach

In this paper, a finite difference approach is being presented as the most reliable technique to investigate the non-linear transverse vibration of an axially moving beam. Firstly, Hamilton’s principle is used to derive the governing hyperbolic partial differential equation (HPDE) of free transverse vibration. Then finite difference along with state space method is used to convert the partial differential equation into a system of coupled first-order ordinary differential equations (ODE’s). Comparison of the proposed finite difference model is made with both the numerical and analytical models. It is noted that the finite difference model is in excellent agreement with the modal analysis approach (analytical solutions) as compared to the generalized integral transform technique GITT (numerical method). A parametric study was also presented to examine the impact of system parameters, such as axial translation speed and flexure rigidities of the beam on the transverse response amplitude, frequencies and instabilities. The transverse vibration of the beam at selected points along its length demonstrates higher-frequency oscillations that corresponds to a lower axial speed. With the increase of beam flexural rigidity, the divergence critical speed increases. Coupled effect of axially moving beam and rotating rolls is also considered.

The high frequency oscillation in orbitofrontal cortex is susceptible to phenethylamine psychedelic 25C–NBOMe in male rats

Serotoninergic psychedelics induced extensive alterations in perception and cognition, which has been attributable to its disruptive effect on oscillatory rhythms of prefrontal cortex. However, there is a lack of information how serotoninergic psychedelics affect the intra-prefrontal network, which intrinsically interact to accomplish perceptual processing. Uncovering the altered neural network caused by psychedelics helps to understand the mechanisms of their psychoactive effects and contribute to develop biological markers of psychedelic effects. In present study, we investigated the effects of substituted phenethylamine psychedelic 25C–NBOMe on neural oscillations in the intra-prefrontal and hippocampal-prefrontal network. The effective dose of 25C–NBOMe (0.1 mg/kg) disrupting sensorimotor gating in male Sprague–Dawley rats was used to observe its effects on neural oscillations in the prelimbic cortex, anterior cingulate cortex, orbitofrontal cortex (OFC) and hippocampus CA1. The power of high frequency oscillation (HFO, 120–150 Hz) was potentiated by 25C–NBOMe selectively in the OFC, with peaking at 20–30 min after treatment. 25C–NBOMe strengthened HFO coherence within the intra-prefrontal, rather than hippocampal-prefrontal network. Potentiated HFO in the OFC had a strong positive correlation with the strengthened inter-prefrontal HFO coherence by 25C–NBOMe. The 25C–NBOMe-induced alterations of rhythmic patterns were prevented by pre-treatment with selective serotonin 2A receptor antagonist MDL100,907. These results demonstrate that OFC rhythmic activity in HFO is relatively susceptible to substituted phenethylamine and potentially drives drug-induced rhythmic coherence within intra-prefrontal regions. Our findings provide additional insight into the neuropathophysiology of the psychoactive effects of psychedelics and indicate that the altered HFO might be applied as a potential biological marker of psychedelic effect.

Calculating quasinormal modes of Schwarzschild anti–de Sitter black holes using the continued fraction method

We investigate the scalar, gravitational, and electromagnetic quasinormal mode spectra of Schwarzschild anti-de Sitter black holes using the numerical continued fraction method. The spectra have similar, almost linear structures. With a few exceptions, the low overtone quasinormal modes are consistent with previously obtained results in the literature that use other numerical techniques. The intermediate and high overtone quasinormal modes, in comparison to the Schwarzschild case, converge very quickly to the asymptotic formulas previously obtained by analytic monodromy techniques. In addition, we find a connection between the analytic asymptotic formulas and the purely imaginary modes. In particular, these formulas can be used to predict the bifurcation of the lowest damped electromagnetic modes. Finally, we find no high overtone quasinormal modes with high oscillation frequency and low damping, which had been previously predicted.

Estimation of High-Frequency Oscillation’s Magnitude and Frequency Based on Multi-Tone FIR Filter

Recently, several high-frequency oscillation (HFO) events have occurred, and have introduced a serious threat to power system stability. It is significant to estimate HFO magnitude and frequency in a fast and accurate way for HFO early warning and mitigation. This paper designs a novel finite impulse response (FIR) filter that is formed by several weighted window function-based FIR filters with different center frequencies, and is named the multi-tone FIR (MTFIR) filter. The frequency error introduced by the MTFIR filter is analyzed, and optimal MTFIR filter parameters are accordingly selected to achieve the smallest frequency error. Performance tests show that the proposed MTFIR filter estimator is more accurate than the conventional FIR filter, the interpolated discrete Fourier transform, and the P-class harmonic phasor estimator in HFO magnitude and frequency estimation. The response time of the proposed estimator is shorter than 20 ms, which meets the IEEE/IEC standard requirement on protection applications.

A hippocampal-entorhinal cortex neuronal network for dynamical mechanisms of epileptic seizure.

Temporal lobe epilepsy (TLE) is thought to be associated with neuronal hyperexcitability in the hippocampal-entorhinal cortical (EC) circuit. Due to the complexity of the hippocampal-EC network connections, the biophysical mechanisms of the different circuits in epilepsy generation and propagation are still not fully established. In this work, we propose a hippocampal-EC neuronal network model to explore the mechanism of epileptic generation. We demonstrate that enhanced excitability of pyramidal neurons in cornu ammonis 3 (CA3) can drive hippocampal-EC to produce a transition from background to seizure state and cause exaggerated phase-amplitude coupling (PAC) phenomenon of theta modulated high-frequency oscillations (HFO) in CA3, cornu ammonis 1 (CA1), dentate gyrus, and EC. Interestingly, PAC strength indirectly responds to the degree of CA3 pyramidal (PY) neuron hyperexcitability, suggesting that PAC can be used as a potential marker of seizures. Furthermore, we find that enhanced synaptic connectivity of mossy cells to granule cells and CA3 PY neurons drives the system to produce epileptic discharges. These two channels may play a key role in mossy fiber sprouting. In particular, the PAC phenomenon of delta-modulated HFO and theta-modulated HFO can be generated according to the different degrees of moss fiber sprouting. Finally, the results suggest that hyperexcitability of stellate cells in EC can lead to seizures, which supports the argument that EC can act as an independent source of seizures. Overall, these results highlight the key role of different circuits in seizures, providing a theoretical basis and new insights into the generation and propagation of TLE.

Support Vector Machine Parameters Optimization for 500 kV Long OHTL Fault Diagnosis

Faults can seriously damage high-voltage (HV) power systems, particularly if they occur on the long overhead transmission line (OHTL) that connects the nuclear power plant (NPP) to the electrical grid. Finding OHTL problems quickly and accurately is essential for the economy, safety, and dependability of the HV power systems. It is essential to pinpoint the problematic phase to avoid unneeded power outages. Thus, one of the most crucial research challenges is now how to identify, classify, and locate OHTL faults. In this study, transient current with high frequency oscillations that arise immediately after a defect at the sending end is investigated in a single-circuit, single-side fed Egyptian 500-kV HV long OHTL. Asymmetric and symmetric faults and locations are also represented in the Alternative Transients Program-Electro Magnetic Transients Program (ATP/EMTP) simulation model under varying fault resistance and inception angles. The proposed solution in this paper is an Optimized Support Vector Machine (OSVM), whose characteristics are optimized via a mutant particle swarm optimization (MPSO) method to detect 500 kV long OHTL faults. The localizer model is also built for practical applications, including power system noise contaminating fault signals. The findings prove that the suggested approach locates the fault in 0.012 seconds from the start of the event, with a 0.0098 percent average percentage error, and without being impacted by differences in fault distance, fault resistance, noise, or fault inception angle. Additionally, the optimised classifier reaches a 99.85% accuracy rate, enhancing line system dependability and advancing nuclear system development.

Neurogenic Supine Hypertension and Cardiovascular Autonomic Dysfunction in Patients with Parkinson's Disease.

Natural history and disease progression in patients with Idiopathic Parkinson's Disease (PD) is quite heterogeneous. Autonomic dysfunction occurs commonly among Idiopathic PD patients. Heart rate variability and ambulatory blood pressure monitoring are used to assess cardiac autonomic dysfunction. The prevalence and magnitude of supine hypertension in Indian PD patients has not been studied to date. The present study aimed to record cardiovascular autonomic functions and supine hypertension in PD patients and to correlate them with the age of onset, duration and severity of the disease, and non-motor symptom burden. The cross-sectional study involved 60 PD patients. Webster rating scale was used to determine the disease severity. Non-motor symptom burden was assessed using the Non-Motor Symptom Scale (NMSS). Ambulatory blood pressure monitoring and heart rate variability parameters determined cardiac autonomic function. Supine hypertension was defined as Systolic Blood Pressure (SBP) ≥150 mmHg and/or DBP ≥90 mmHg. Less than 10% decrease or even increase in blood pressure during the night were classified as non-dippers. Pearson coefficient was used appropriately to establish correlation. P ≤ 0.05 was considered significant. Age of onset was 61.2 ± 8.7 years and duration of disease was 1.7 ± 1.1 years. Mean Webster and non-motor symptom scores were 12.7 ± 4.4 and 15.5 ± 8.0, respectively. About 50 patients (83%) were non-dipper, while 32 (53%) had supine hypertension. Low Frequency oscillations (LF) (r = 0.28), High Frequency oscillations (HF) (r = 0.29), Standard Deviation NN intervals (SDNN) (0.26), and Root Mean Squared Successive Differences of NN intervals (RMSSD) (r = 0.28) correlated significantly with non-motor symptoms scale. LF (r = -0.39), HF (r = -0.43), SDNN (-0.40), RMSSD (r = -0.41), NN50 (r = -0.38), PNN50 (r = -0.42), mean SBP (r = 0.26), and mean DBP (r = 0.33) correlated significantly with disease duration. PNN50 (r = -0.255), mean SBP (r = -0.29), and mean DBP (r = -0.27) correlated significantly with age at onset. Awareness regarding neurogenic supine hypertension is needed as it occurs commonly among Indian PD patients. Heart rate variability (HRV) parameters and ambulatory blood pressure are of significant help in the detection of early cardiovascular autonomic dysfunction and correlate significantly with disease duration and non-motor symptom burden among PD patients.

Electrocorticography for the Evaluation of Focus Resection

Electrocorticography(ECoG)with intracranial electrodes has a higher spatial resolution and higher sensitivity than conventional electroencephagrahy. Chronic VIDEO-ECoG with subdural grid electrodes has been used to determine the resection border of epileptic focus, and to evaluate cortical function prior to resective surgery. Recording multiple seizures is necessary to determine whether they are the same as habitual seizures and whether they are reproducible, to allow subsequent identification of the seizure onset zone. It is also necessary to understand the ictal ECoG patterns of various seizure onsets. Recent advances in engineering technology have made wideband(0.01 Hz-600Hz)analysis possible. The resection of the area with the ictal DC shift and high frequency oscillation is reported to improve surgical outcome. Although the procedure of subdural grid insertion is technically easy, high rates of complications, such as infections and bleeding, have been reported. Intraoperative acute ECoG was used to validate the extent of resection area. Overall, intraoperative ECoG is greatly affected by anesthetics, and the interictal epileptic discharge should be evaluated carefully.

Effects of Palmitoylethanolamide Combined with Luteoline on High Frequency Oscillations and GABAergic Transmission in Patients with Frontotemporal Dementia

Effects of Palmitoylethanolamide Combined with Luteoline on High Frequency Oscillations and GABAergic Transmission in Patients with Frontotemporal Dementia

Adaptive Wall Shear Stress Imaging in Phantoms, Simulations and In Vivo.

WSS measurement is challenging since it requires sensitive flow measurements at a distance close to the wall. The aim of this study is to develop an ultrasound imaging technique which combines vector flow imaging with an unsupervised data clustering approach that automatically detects the region close to the wall with optimally linear flow profile, to provide direct and robust WSS estimation. The proposed technique was evaluated in phantoms, mimicking normal and atherosclerotic vessels, and spatially registered Fluid Structure Interaction (FSI) simulations. A relative error of 6.7% and 19.8% was obtained for peak systolic (WSSPS) and end diastolic (WSSED) WSS in the straight phantom, while in the stenotic phantom, a good similarity was found between measured and simulated WSS distribution, with a correlation coefficient, R, of 0.89 and 0.85 for WSSPS and WSSED, respectively. Moreover, the feasibility of the technique to detect pre-clinical atherosclerosis was tested in an atherosclerotic swine model. Six swines were fed atherogenic diet, while their left carotid artery was ligated in order to disturb flow patterns. Ligated arterial segments that were exposed to low WSSPS and WSS characterized by high frequency oscillations at baseline, developed either moderately or highly stenotic plaques (p < 0.05). Finally, feasibility of the technique was demonstrated in normal and atherosclerotic human subjects. Atherosclerotic carotid arteries with low stenosis had lower WSSPS as compared to control subjects (p < 0.01), while in one subject with high stenosis, elevated WSS was found on an arterial segment, which coincided with plaque rupture site, as determined through histological examination.

The lower hybrid frequency range wave emission in the ohmic discharge of the FT-2 tokamak

The paper presents observations of plasma intermediate frequency range wave emission ((200--1000) MHz) performed in ohmic discharge of the FT-2 tokamak. The dependencies of the RF signal amplitude and spectrum on the plasma parameters and on the location of the probes are presented. Two possible explanations for this effect is proposed. One of them is related to the distortion of the electron distribution function due to the strong ripple of the magnetic field in the FT-2 tokamak. Second one is related to the existence of a beam of run-away electrons, the buildup of a fan instability responsible for the generation of synchrotron radiation in the range (10-80) GHz, and a complex chain of nonlinear decay instabilities leading to such a strong decrease in the frequency of the observed oscillations. Keywords: tokamak, lower hybrid current drive, high frequency oscillations, parametric decay instabilities.

Genetic Algorithm Assisted Parametric Design of Splitting Inductance in High Frequency GaN-Based Dual Active Bridge Converter

Splitting and placing interfacing inductance on both sides of the transformer has been proven to be an effective method, which extends the zero-voltage switching region for all the switching devices in the dual active bridge (DAB) converter. With the trend toward operating in higher frequency, achieving higher power density and higher efficiency, the converter model becomes more complex due to the non-negligible parasitic components that brings new challenges to DAB converter design. Traditional analytical methods have made it hard to imitate the proposed converter easily and precisely. Thus, artificial intelligence techniques are able to be utilized to assist the design process. When considering the converter system as a gray-box model, the metaheuristic algorithm can be implemented for the targeted design inside such a gray-box. In this article, a genetic algorithm (GA) is employed in the DAB converter parametric design with an explicit fitness desire to help in discovering the high frequency oscillation (HFO) problem. Consequently, the splitting inductance tuning method is proposed for eliminating the HFO problem and minimizing inductors’ loss. The methodology of implementing GA into converter parametric design, and the proposed splitting inductance tuning method are introduced and verified with a 1 MHz gallium nitride high-electron-mobility transistor based DAB converter prototype. The comparitive experimental results prove the effectiveness of the splitting inductance tuning method and achieve 4% efficiency enhancement with 200 W power delivering.

Harmonic State-Space Based AC-Side Impedance Model of MMC and High Frequency Oscillation Characteristics Analysis

Recently, high-frequency oscillation of the modular multilevel converter (MMC) based high-voltage direct current (HVDC) projects has attracted great attentions. In order to analyze the small-signal stability, this paper uses the harmonic state-space (HSS) method to establish a detailed frequency domain impedance model of the AC-side of the HVDC transmission system, which considers the internal dynamic characteristics. In addition, the suggested model is also used to assess the system's high-frequency oscillation mechanism, and the effects of the MMC current inner loop control, feedforward voltage links, and control delay on the high-frequency impedance characteristics and the effect of higher harmonic components. Finally, three oscillation suppression schemes are analyzed for the oscillation problems occurring in actual engineering, and a simplified impedance model considering only the high-frequency impedance characteristics is established to compare the suppression effect with the detailed impedance model to prove its reliability.

Transcranial focused ultrasound and electrocorticography-based closed-loop epilepsy control system for an awake rat model

Abstract Neurostimulation with closed-loop interaction is one of the clinical solutions for patients with drug-resistant epilepsy. However, there are growing demands for an epilepsy control system with minimal invasiveness. Transcranial focused ultrasound (tFUS) is a promising non-invasive neuromodulation technique for controlling epileptic seizures due to its superior spatial specificity and depth penetrability. Here, we demonstrated a tFUS-based closed-loop system in combination with electrocorticography (ECoG), which provides precise monitoring of epileptic discharge for epileptic patients. In-house built 16-ch ECoG electrodes were attached to the Sprague-Dawley rat’s dura for detecting seizure spike-wave proceeding high-frequency oscillations (HFO) and monitoring epileptic discharges. After recovery from the surgery, kainic acid (5 mg/kg) was injected to generate a temporal lobe epilepsy rat model. An ultrasonic transducer operating at a fundamental frequency of 300 kHz was attached to the scalp for tFUS stimulation, which was automatically controlled by the system based on the HFO detection algorithm with real-time ECoG monitoring. The closed-loop tFUS stimulation on the right hippocampus with 40 Hz pulse-repetition frequency (PRF) and 5 % duty cycle induced the diminution of the duration of seizure spike-wave and the suppression of the power of brain oscillations such as theta, gamma bands from the bilateral hemisphere, compared to sham stimulation. Furthermore, the developed system is able to adjust the sonication protocol by monitoring seizure spike-wave. We therefore could provide optimized control of tFUS stimulation for seizure suppression. We demonstrated an ultrasound-based closed-loop system inhibiting epileptiform activity by providing tFUS stimulation before the generation of an epileptic spike-wave. The proposed system in this study shows the potential for developing a system that provides non-invasive seizure control without additional surgical burden for patients who are wearing medical brain implants such as ECoG or other types of intracranial EEG electrodes. Research Category and Technology and Methods Basic Research: 6. Pulsed Ultrasound (pUS) Keywords: transcranial focused ultrasound, closed-loop control, epilepsy, ECoG