Positive memory increases cataplexy-like behaviors in narcolepsy mice as revealed using conditioned place preference test

To examine the pathological effect of a mesial temporal seizure onset zone (SOZ) on local and inter-regional response to faces in the amygdala and other structures of the temporal lobe. Intracranial EEG data was obtained from the amygdala, hippocampus, fusiform gyrus and parahippocampal gyrus of nine patients with drug-refractory epilepsy during visual stimulation with faces and mosaics. We analyzed event-related potentials (ERP), gamma frequency power, phase-amplitude coupling and phase-slope-index and compared the results between patients with versus without a mesial temporal SOZ. In the amygdala and fusiform gyrus, faces triggered higher ERP amplitudes compared to mosaics in both patient groups and higher gamma power in patients without a mesial temporal SOZ. In the hippocampus, famous faces triggered higher gamma power for both groups combined but did not affect ERPs in either group. The differentiated ERP response to famous faces in the parahippocampal gyrus was more pronounced in patients without a mesial temporal SOZ. Phase-amplitude coupling and phase-slope-index results yielded bidirectional modulation between amygdala and fusiform gyrus, and predominately unidirectional modulation between parahippocampal gyrus and hippocampus. A mesial temporal SOZ was associated with an impaired response to faces in the amygdala, fusiform gyrus and parahippocampal gyrus in our patients. Compared to this, the response to faces in the hippocampus was impaired in patients with, as well as without, a mesial temporal SOZ. Our results support existing evidence for face processing deficits in patients with a mesial temporal SOZ and suggest the pathological effect of a mesial temporal SOZ on the amygdala to play a pivotal role in this matter in particular.     

Electroencephalograms in epilepsy: analysis and seizure prediction within the framework of Lyapunov theory

Epileptic seizures are defined as the clinical manifestation of excessive and hypersynchronous activity of neurons in the cerebral cortex and represent one of the most frequent malfunctions of the human central nervous system. Therefore, the search for precursors and predictors of a seizure is of utmost clinical relevance and may even guide us to a deeper understanding of the seizure generating mechanisms. We extract chaos-indicators such as Lyapunov exponents and Kolmogorov entropies from different types of electroencephalograms (EEGs): this covers mainly intracranial EEGs (semi-invasive and invasive recording techniques), but also scalp-EEGs from the surface of the skin. Among the analytical methods we tested up to now, we find that the spectral density of the local expansion exponents is best suited to predict the onset of a forthcoming seizure. We also evaluate the time-evolution of the dissipation in these signals: it exhibits strongly significant variations that clearly relate to the time relative to a seizure onset. This article is mainly devoted to an assessment of these methods with respect to their sensitivity to EEG changes, e.g., prior to a seizure. Further, we investigate interictal EEGs (i.e., far away from a seizure) in order to characterize their more general properties, such as the convergence of the reconstructed quantities with respect to the number of phase space dimensions. Generally we use multichannel reconstruction, but we also present a comparison with the delay-embedding technique.     

Epileptic Seizure Detection Using Geometric Features Extracted from SODP Shape of EEG Signals and AsyLnCPSO-GA

Epilepsy is a neurological disorder that is characterized by transient and unexpected electrical disturbance of the brain. Seizure detection by electroencephalogram (EEG) is associated with the primary interest of the evaluation and auxiliary diagnosis of epileptic patients. The aim of this study is to establish a hybrid model with improved particle swarm optimization (PSO) and a genetic algorithm (GA) to determine the optimal combination of features for epileptic seizure detection. First, the second-order difference plot (SODP) method was applied, and ten geometric features of epileptic EEG signals were derived in each frequency band (δ, θ, α and β), forming a high-dimensional feature vector. Secondly, an optimization algorithm, AsyLnCPSO-GA, combining a modified PSO with asynchronous learning factor (AsyLnCPSO) and the genetic algorithm (GA) was proposed for feature selection. Finally, the feature combinations were fed to a naïve Bayesian classifier for epileptic seizure and seizure-free identification. The method proposed in this paper achieved 95.35% classification accuracy with a tenfold cross-validation strategy when the interfrequency bands were crossed, serving as an effective method for epilepsy detection, which could help clinicians to expeditiously diagnose epilepsy based on SODP analysis and an optimization algorithm for feature selection.     

Strain engineering of graphene nanoribbons: pseudomagnetic versus external magnetic fields

Bandgap opening due to strain engineering is a key architect for making graphene’s optoelectronic, straintronic, and spintronic devices. We study the bandgap opening due to strain induced ripple waves and investigate the interplay between pseudomagnetic fields and externally applied magnetic fields on the band structures and spin relaxation in graphene nanoribbons (GNRs). We show that electron-hole bands of GNRs are highly influenced (i.e. level crossing of the bands are possible) by coupling two combined effects: pseudomagnetic fields (PMF) originating from strain tensor and external magnetic fields. In particular, we show that the tuning of the spin-splitting band extends to large externally applied magnetic fields with increasing values of pseudomagnetic fields. Level crossings of the bands in strained GNRs can also be observed due to the interplay between pseudomagnetic fields and externally applied magnetic fields. We also investigate the influence of this interplay on the electromagnetic field mediated spin relaxation mechanism in GNRs. In particular, we show that the spin hot spot can be observed at approximately B = 65 T (the externally applied magnetic field) and B₀ = 53 T (the magnitude of induced pseudomagnetic field due to ripple waves) which may not be considered as an ideal location for the design of straintronic devices. Our analysis might be used for tuning the bandgaps in strained GNRs and utilized to design the optoelectronic devices for straintronic applications.     

EEG-fMRI mapping of asymmetrical delta activity in a patient with refractory epilepsy is concordant with the epileptogenic region determined by intracranial EEG

We studied a patient with refractory focal epilepsy using continuous EEG-correlated fMRI. Seizures were characterized by head turning to the left and clonic jerking of the left arm, suggesting a right frontal epileptogenic region. Interictal EEG showed occasional runs of independent nonlateralized slow activity in the delta band with right frontocentral dominance and had no lateralizing value. Ictal scalp EEG had no lateralizing value. Ictal scalp EEG suggested right-sided central slow activity preceding some seizures. Structural 3-T MRI showed no abnormality. There was no clear epileptiform abnormality during simultaneous EEG-fMRI. We therefore modeled asymmetrical EEG delta activity at 1-3 Hz near frontocentral electrode positions. Significant blood oxygen level-dependent (BOLD) signal changes in the right superior frontal gyrus correlated with right frontal oscillations at 1-3 Hz but not at 4-7 Hz and with neither of the two frequency bands when derived from contralateral or posterior electrode positions, which served as controls. Motor fMRI activations with a finger-tapping paradigm were asymmetrical: they were more anterior for the left hand compared with the right and were near the aforementioned EEG-correlated signal changes. A right frontocentral perirolandic seizure onset was identified with a subdural grid recording, and electric stimulation of the adjacent contact produced motor responses in the left arm and after discharges. The fMRI localization of the left hand motor and the detected BOLD activation associated with modeled slow activity suggest a role for localization of the epileptogenic region with EEG-fMRI even in the absence of clear interictal discharges.     

Directional photoemission from tungsten

Photoemission energy distribution spectra have been scanned for photoelectrons emitted normal to two different crystal faces of tungsten, namely (100) and (110). The energy distributions and the derivative spectra show large differences between emission from the two faces. Whereas strong surface state emission is observed from the (100) face, no surface states are associated with the (110) face. The spectra show features characteristic of direct and also nondirect transitions, but these features appear very different for the two faces. Using existing band structure calculations, the spectral structure is assigned to electronic transitions between bands along the Δ axis for the (100) face and the Σ axis for the (110) face. The experiments show that directional photoemission spectra taken normal to a crystal surface make it possible to investigate electronic energy bands along symmetry directions in the Brillouin zone.     

Stochastic processes of demarkovization and markovization in chaotic signals of human brain electric activity from EEGs during epilepsys

We study the stochastic processes of markovization and demarkovization in chaotic signals of human electroencephalograms (EEGs) during epilepsy using various measures of demarkovization and markovization, namely, the statistical spectrum of a non-Markovity parameter, power spectra of the time correlation function and memory functions of junior orders, and local relaxation and kinetic parameters. The results demonstrate the superiority of the new measures in comparison to the traditional nonlinear measures. We conclude that the applied measures are more appropriate for the quantification of markovization and demarkovization in EEG data and the prediction of epilepsy seizure.     

Design constraints for wavelength-division-multiplexed filters with minimal side-channel impairment

The design of wavelength-division-multiplexed (WDM) filters requires control of both the attributes of the filter within the reflection band and the filter's effects on adjacent bands. Causality arguments are used to give the minimum dispersion that can be achieved in the transmission of an adjacent channel in terms of the bandwidth, sidelobe suppression, and channel spacing of WDM filters. The ripple in the side-channel dispersion is also related to the sidelobe properties. Results for a synthesized grating design and its calculated spectrum are compared with the theoretical limits on dispersion.     

Direct observation of broken time-reversal symmetry on the surface of a magnetically doped topological insulator

We study interference patterns of a magnetically doped topological insulator Bi(2-x)Fe(x)Te(3+d) by using Fourier transform scanning tunneling spectroscopy and observe several new scattering channels. A comparison with angle-resolved photoemission spectroscopy allows us to unambiguously ascertain the momentum-space origin of distinct dispersing channels along high-symmetry directions and identify those originating from time-reversal symmetry breaking. Our analysis also reveals that the surface state survives far above the energy where angle-resolved photoemission spectroscopy finds the onset of continuum bulk bands.     

Channel weights for speech recognition in cochlear implant users

The purpose of this study was to develop and validate a method of estimating the relative "weight" that a multichannel cochlear implant user places on individual channels, indicating its contribution to overall speech recognition. The correlational method as applied to speech recognition was used both with normal-hearing listeners and with cochlear implant users fitted with six-channel speech processors. Speech was divided into frequency bands corresponding to the bands of the processor and a randomly chosen level of corresponding filtered noise was added to each channel on each trial. Channels in which the signal-to-noise ratio was more highly correlated with performance have higher weights, and conversely, channels in which the correlations were smaller have lower weights. Normal-hearing listeners showed approximately equal weights across frequency bands. In contrast, cochlear implant users showed unequal weighting across bands, and varied from individual to individual with some channels apparently not contributing significantly to speech recognition. To validate these channel weights, individual channels were removed and speech recognition in quiet was tested. A strong correlation was found between the relative weight of the channel removed and the decrease in speech recognition, thus providing support for use of the correlational method for cochlear implant users.     

光纤光栅非线性时延对啁啾的电视信号的影响

分析了有线电视系统中,用作色散补偿的光纤光栅因色散抖动对信号载波互调比产生的影响,结果显示色散抖动对有线电视信号互调比的影响随拦动幅度、抖动周期、信道数目的加而增加,信道频率的分布也对其的影响。对光栅的色散特性进行数值估算,发现常耦合系数线性啁啾光栅不能用的有线电视系统中进行色散补偿。     

Design of a Common Ellipsoidal Mirror for the Focalization of Several Radioastronomic Bands: New Method and Application to Three Bands

The design of a common ellipsoidal mirror for the focalization of several radioastronomic bands, by means of a straightforward method, is presented. Three bands centered at 100, 80 and 45 GHz are chosen for the validation of the method. Quasi-optics theory is used to design an optical system that can focalize several bands with the minimum possible optic elements, and also to share the maximum of them. Lenses, mirrors, feeder dimensions and the distances among each component necessaries for the focalization in each band are calculated. The simultaneous design in several radioastronomic observation bands reduces the cost of manufacturing, the total number of optic elements and the density of optical elements on the receiver cabin.     

Clinical correlations with hippocampal atrophy

There is now a consensus that magnetic resonance imaging (MRI) is a sensitive and specific indicator of mesial temporal sclerosis (MTS) in patients with partial epilepsy. MTS is the most common pathological finding underlying the epileptogenic zone in patients undergoing temporal lobe surgery for medically refractory partial seizures. MRI-based hippocampal volumetric studies (i.e., quantitative MRI), has been shown to provide objective evidence for hippocampal atrophy in patients with MTS. The hippocampal volume in the epileptic temporal lobe has correlated with the neuronal cell densities in selected hippocampal subfields. A history of febrile seizures in childhood and age of unprovoked seizure onset have been associated with MRI-based hippocampal volumetry. There is conflicting evidence regarding the relationship between the duration of the seizure disorder and volumetry. Quantitative MRI has compared favorably to other noninvasive techniques (e.g., scalp-recorded EEG), in indicating the diagnosis of medical temporal lobe epilepsy (MTLE). MRI-identified hippocampal atrophy has also been a favorable prognostic indicator of seizure outcome after temporal lobe surgery. The presence of hippocampal atrophy appears to serve an in vivo surrogate for the presence of MTS.     

Ripple depth and density resolution of rippled noise

Depth resolution of spectral ripples was measured in normal humans using a phase-reversal test. The principle of the test was to find the lowest ripple depth at which an interchange of peak and trough position (the phase reversal) in the rippled spectrum is detectable. Using this test, ripple-depth thresholds were measured as a function of ripple density of octave-band rippled noise at center frequencies from 0.5 to 8 kHz. The ripple-depth threshold in the power domain was around 0.2 at low ripple densities of 4-5 relative units (center-frequency-to-ripple-spacing ratio) or 3-3.5 ripples/oct. The threshold increased with the ripple density increase. It reached the highest possible level of 1.0 at ripple density from 7.5 relative units at 0.5 kHz center frequency to 14.3 relative units at 8 kHz (5.2 to 10.0 ripple/oct, respectively). The interrelation between the ripple depth threshold and ripple density can be satisfactorily described by transfer of the signal by frequency-tuned auditory filters.     

Long-time behavior of sand ripples induced by water shear flow

The formation of sand ripples under water shear flow in a narrow annular channel and the approach of the ripple pattern towards a steady state were studied experimentally. Four results are obtained: i) The mean amplitude, the average drift velocity and the mean sediment transport rate of the evolving bed shape are strongly related. A quantitative characterization of this relation is given. ii) The ripple pattern reaches a stationary state with a finite ripple amplitude and wavelength. The time needed to reach the state depends on the shear stress and may be several days. iii) The onset of ripple formation is determined by the bed shear stress, but it seems neither to depend on the grain diameter nor on the depth of the water layer. iv) The ripple amplitude, drift velocity and sediment transport in this stationary state depend on the grain size. This dependency is neither captured by the particle Reynolds number nor by the Shields parameter: an empirical scaling law is presented instead.     

基于非成像光学环带法的反射器设计

应用非成像光学的原理,介绍一种简单、实用的旋转对称反射器的自由曲面设计方法环带法。提出环带法的设计思路,将光源的出光分布和灯具光学组件的出光分布分别按一定的角度间隔平均划分为不同的环带区间,根据不同环带区的光通量值差异进行一系列的对比分析,从而确定光源出射光线与灯具出射光源的对应关系,最终确定反射面的斜率,求解由斜率构成的二元一次方程组便可得到反射曲线的线形。描述了环带法的详细设计步骤和细节,并通过针对LED光源的具体应用实例加以验证,最终实现对光源的精确配光,设计吻合程度可达98.4%。     

Entropy Measures of Electroencephalograms towards the Diagnosis of Psychogenic Non-Epileptic Seizures

Psychogenic non-epileptic seizures (PNES) may resemble epileptic seizures but are not caused by epileptic activity. However, the analysis of electroencephalogram (EEG) signals with entropy algorithms could help identify patterns that differentiate PNES and epilepsy. Furthermore, the use of machine learning could reduce the current diagnosis costs by automating classification. The current study extracted the approximate sample, spectral, singular value decomposition, and Renyi entropies from interictal EEGs and electrocardiograms (ECG)s of 48 PNES and 29 epilepsy subjects in the broad, delta, theta, alpha, beta, and gamma frequency bands. Each feature-band pair was classified by a support vector machine (SVM), k-nearest neighbour (kNN), random forest (RF), and gradient boosting machine (GBM). In most cases, the broad band returned higher accuracy, gamma returned the lowest, and combining the six bands together improved classifier performance. The Renyi entropy was the best feature and returned high accuracy in every band. The highest balanced accuracy, 95.03%, was obtained by the kNN with Renyi entropy and combining all bands except broad. This analysis showed that entropy measures can differentiate between interictal PNES and epilepsy with high accuracy, and improved performances indicate that combining bands is an effective improvement for diagnosing PNES from EEGs and ECGs.     

White matter abnormalities in children and adolescents with temporal lobe epilepsy

Background and Purpose

The widespread propagation of synchronized neuronal firing in seizure disorders may affect cortical and subcortical brain regions. Diffusion tensor imaging (DTI) can noninvasively quantify white matter integrity. The purpose of this study was to investigate the abnormal changes of white matter in children and adolescents with focal temporal lobe epilepsy (TLE) using DTI.

Materials and Methods

Eight patients with clinically diagnosed TLE and eight age- and sex-matched healthy controls were studied. DTI images were obtained with a 3-T magnetic resonance imaging scanner. The epileptic foci were localized with magnetoencephalography. Fractional anisotropy (FA), mean diffusivity (MD), parallel (λ_||) and perpendicular (λ_⊥) diffusivities in the genu of the corpus callosum, splenium of the corpus callosum (SCC), external capsule (EC), anterior limbs of the internal capsule (AIC), and the posterior limbs of the internal capsule (PIC) were calculated. The DTI parameters between patients and controls were statistically compared. Correlations of these DTI parameters of each selected structure with age of seizure onset and duration of epilepsy were analysed.

Results

In comparison to controls, both patients' seizure ipsilateral and contralateral had significantly lower FA in the AIC; PIC and SCC and higher MD, λ_|| and λ_⊥ in the EC, AIC, PIC and SCC. The MD, λ_|| and λ_⊥ were significantly correlated with age of seizure onset in the EC and PIC. λ_|| was significantly correlated with the duration of epilepsy in the EC and PIC.

Conclusion

The results of the present study indicate that children and adolescents with TLE had significant abnormalities in the white matter in the hemisphere with seizure foci. Furthermore, these abnormalities may extend to the other brain hemisphere. The age of seizure onset and duration of epilepsy may be important factors in determining the extent of influence of children and adolescents TLE on white matter.     

Continuous EEG-fMRI in patients with partial epilepsy and focal interictal slow-wave discharges on EEG

Purpose

To verify whether in patients with partial epilepsy and routine electroenecephalogram (EEG) showing focal interictal slow-wave discharges without spikes combined EEG–functional magnetic resonance imaging (fMRI) would localize the corresponding epileptogenic focus, thus providing reliable information on the epileptic source.

Methods

Eight patients with partial epileptic seizures whose routine scalp EEG recordings on presentation showed focal interictal slow-wave activity underwent EEG–fMRI. EEG data were continuously recorded for 24 min (four concatenated sessions) from 18 scalp electrodes, while fMRI scans were simultaneously acquired with a 1.5-Tesla magnetic resonance imaging (MRI) scanner. After recording sessions and MRI artefact removal, EEG data were analyzed offline. We compared blood oxygen level-dependent (BOLD) signal changes on fMRI with EEG recordings obtained at rest and during activation (with and without focal interictal slow-wave discharges).

Results

In all patients, when the EEG tracing showed the onset of focal slow-wave discharges on a few lateralized electrodes, BOLD-fMRI activation in the corresponding brain area significantly increased. We detected significant concordance between focal EEG interictal slow-wave discharges and focal BOLD activation on fMRI. In patients with lesional epilepsy, the epileptogenic area corresponded to the sites of increased focal BOLD signal.

Conclusions

Even in patients with partial epilepsy whose standard EEGs show focal interictal slow-wave discharges without spikes, EEG–fMRI can visualize related focal BOLD activation thus providing useful information for pre-surgical planning.     

Gender and speaker identification as a function of the number of channels in spectrally reduced speech

Considerable research on speech intelligibility for cochlear-implant users has been conducted using acoustic simulations with normal-hearing subjects. However, some relevant topics about perception through cochlear implants remain scantly explored. The present study examined the perception by normal-hearing subjects of gender and identity of a talker as a function of the number of channels in spectrally reduced speech. Two simulation strategies were compared. They were implemented by two different processors that presented signals as either the sum of sine waves at the center of the channels or as the sum of noise bands. In Experiment 1, 15 subjects determined the gender of 40 talkers (20 males + 20 females) from a natural utterance processed through 3, 4, 5, 6, 8, 10, 12, and 16 channels with both processors. In Experiment 2, 56 subjects matched a natural sentence uttered by 10 talkers with the corresponding simulation replicas processed through 3, 4, 8, and 16 channels for each processor. In Experiment 3, 72 subjects performed the same task but different sentences were used for natural and processed stimuli. A control Experiment 4 was conducted to equate the processing steps between the two simulation strategies. Results showed that gender and talker identification was better for the sine-wave processor, and that performance through the noise-band processor was more sensitive to the number of channels. Implications and possible explanations for the superiority of sine-wave simulations are discussed.