Sharp Waveforms Research Articles

Neuromagnetic high frequency spikes are a new and noninvasive biomarker for localization of epileptogenic zones

ObjectiveOne barrier hindering high frequency brain signals (HFBS, >80 Hz) from wide clinical applications is that the brain generates both pathological and physiological HFBS. This study was to find specific biomarkers for localizing epileptogenic zones (EZs). MethodsTwenty three children with drug-resistant epilepsy and age/sex matched healthy controls were studied with magnetoencephalography (MEG). High frequency oscillations (HFOs, > 4 oscillatory waveforms) and high frequency spikes (HFSs, > 1 spiky or sharp waveforms) in 80–250 Hz and 250–600 Hz bands were blindly detected with an artificial intelligence method and validated with visual inspection. The magnitude of HFOs and HFSs were quantified with spectral analyses. Sources of HFSs and HFOs were localized and compared with clinical EZs determined by invasive recordings and surgical outcomes. ResultsHFOs in 80–250 Hz and 250–600 Hz were identified in both epilepsy patients (18/23, 12/23, respectively) and healthy controls (6/23, 4/23, respectively). HFSs in 80–250 Hz and 250–600 Hz were detected in patients (16/23, 11/23, respectively) but not in healthy controls. A combination of HFOs and HFSs localized EZs for 22 (22/23, 96%) patients. ConclusionsThe results indicate, for the first time, that HFSs are a newer and more specific biomarker than HFOs for localizing EZs because HFOs appeared in both epilepsy patients and healthy controls while HFSs appeared only in epilepsy patients.

Strong correlation between doppler snuffbox resistive index and systemic vascular resistance in septic patients

PurposeTo compare systemic vascular resistance index (SVRI) as measured by invasive transpulmonary indicator dilution (TPID) and non-invasive Doppler-derived resistive index in septic patients. MethodsWe measured the snuffbox resistive index (SBRI) in both hands of septic patients who received hemodynamic monitoring by TPID prospectively. ResultsThirty-six patients with septic shock were enrolled (median acute physiology and chronic health evaluation II score: 23; median age: 64 years). Four SBRI values were measured in each patient, for a total of 96 patient days and 951 ultrasound measurements. The correlation coefficients between SVRI and the four SBRI values were all higher than 0.87 (p < .001). A higher SVRI was associated with sharp waveforms and reversed diastolic flow. A resistive index (RI) of 0.97 was the lower limit of normal SVRI (1700 dyn*s*cm−5*m2), and an RI of 1.1 was the upper limit of normal SVRI (2400 dyn*s*cm−5*m2). ConclusionsUsing ultrasound to measure RI is a noninvasive, inexpensive, reliable method to evaluate peripheral vascular resistance in septic patients, and it is highly correlated with SVRI. In addition, SBRI can be used to evaluate peripheral circulatory disturbances in septic patients.

Distinct phase-amplitude couplings distinguish cognitive processes in human attention

Spatial attention is the cognitive function that coordinates the selection of visual stimuli with appropriate behavioral responses. Recent studies have reported that phase-amplitude coupling (PAC) of low and high frequencies covaries with spatial attention, but differ on the direction of covariation and the frequency ranges involved. We hypothesized that distinct phase-amplitude frequency pairs have differentiable contributions during tasks that manipulate spatial attention. We investigated this hypothesis with electrocorticography (ECoG) recordings from participants who engaged in a cued spatial attention task. To understand the contribution of PAC to spatial attention we classified cortical sites by their relationship to spatial variables or behavioral performance. Local neural activity in spatial sites was sensitive to spatial variables in the task, while local neural activity in behavioral sites correlated with reaction time. We found two PAC frequency clusters that covaried with different aspects of the task. During a period of cued attention, delta-phase/high-gamma (DH) PAC was sensitive to cue direction in spatial sites. In contrast, theta-alpha-phase/beta-low-gamma-amplitude (TABL) PAC robustly correlated with future reaction times in behavioral sites. Finally, we investigated the origins of TABL PAC and found it corresponded to behaviorally relevant, sharp waveforms, which were also coupled to a low frequency rhythm. We conclude that TABL and DH PAC correspond to distinct mechanisms during spatial attention tasks and that sharp waveforms are elements of a coupled dynamical process.

Dual origins of measured phase-amplitude coupling reveal distinct neural mechanisms underlying episodic memory in the human cortex

Phase-amplitude coupling (PAC) is hypothesized to coordinate neural activity, but its role in successful memory formation in the human cortex is unknown. Measures of PAC are difficult to interpret, however. Both increases and decreases in PAC have been linked to memory encoding, and PAC may arise due to different neural mechanisms. Here, we use a waveform analysis to examine PAC in the human cortex as participants with intracranial electrodes performed a paired associates memory task. We found that successful memory formation exhibited significant decreases in left temporal lobe and prefrontal cortical PAC, and these two regions exhibited changes in PAC within different frequency bands. Two underlying neural mechanisms, nested oscillations and sharp waveforms, were responsible for the changes in these regions. Our data therefore suggest that decreases in measured cortical PAC during episodic memory reflect two distinct underlying mechanisms that are anatomically segregated in the human brain.

Non-Sinusoidal Activity Can Produce Cross-Frequency Coupling in Cortical Signals in the Absence of Functional Interaction between Neural Sources.

The analysis of cross-frequency coupling (CFC) has become popular in studies involving intracranial and scalp EEG recordings in humans. It has been argued that some cases where CFC is mathematically present may not reflect an interaction of two distinct yet functionally coupled neural sources with different frequencies. Here we provide two empirical examples from intracranial recordings where CFC can be shown to be driven by the shape of a periodic waveform rather than by a functional interaction between distinct sources. Using simulations, we also present a generalized and realistic scenario where such coupling may arise. This scenario, which we term waveform-dependent CFC, arises when sharp waveforms (e.g., cortical potentials) occur throughout parts of the data, in particular if they occur rhythmically. Since the waveforms contain both low- and high-frequency components, these components can be inherently phase-aligned as long as the waveforms are spaced with appropriate intervals. We submit that such behavior of the data, which seems to be present in various cortical signals, cannot be interpreted as reflecting functional modulation between distinct neural sources without additional evidence. In addition, we show that even low amplitude periodic potentials that cannot be readily observed or controlled for, are sufficient for significant CFC to occur.

EPILEPTIFORM SPIKE DETECTION VIA CONVOLUTIONAL NEURAL NETWORKS.

The EEG of epileptic patients often contains sharp waveforms called "spikes", occurring between seizures. Detecting such spikes is crucial for diagnosing epilepsy. In this paper, we develop a convolutional neural network (CNN) for detecting spikes in EEG of epileptic patients in an automated fashion. The CNN has a convolutional architecture with filters of various sizes applied to the input layer, leaky ReLUs as activation functions, and a sigmoid output layer. Balanced mini-batches were applied to handle the imbalance in the data set. Leave-one-patient-out cross-validation was carried out to test the CNN and benchmark models on EEG data of five epilepsy patients. We achieved 0.947 AUC for the CNN, while the best performing benchmark model, Support Vector Machines with Gaussian kernel, achieved an AUC of 0.912.

Dynamics of electroencephalogram (EEG) in different stages of chronic kidney disease.

To study Electroencephalogram (EEG) in different stages of chronic kidney disease (CKD). This observational study was carried out in the Department of Medicine, Jawaharlal Nehru Medical College, Sawangi (Meghe), Wardha conducted over a period of 24 months, spanning from August 2011 to August 2013. Eighty three cases of CKD at different stages were studied. EEG was done in all the subjects and the various EEG dynamics like morphometric waveform patterns, symmetricity, amplitude were recorded and compared with the different stages of CKD. We found that characteristic changes were observed with increasing severity of CKD. Slow delta wave patterns were more prominent in stage 5 (p<0.0001), asymmetric discharges, dysthymia, sharp wave transients and low amplitude wave forms were more prominent beyond Stage 4 (p<0.0001). EEG can be used as an effective tool for detection of subclinical or latent uremic encephalopathy. EEG findings which are characteristics of uremic encephalopathy can be present in CKD patients without overt signs of encephalopathy. So, EEG can be used as a prognostic indicator of response to clinical therapy of CKD.

Evaluation of Postoperative Sharp Waveforms Through EEG and Magnetoencephalography

EEGs obtained after craniotomy are difficult to read because of a breach rhythm consisting of unfiltered sharply contoured physiologic waveforms that can mimic interictal epileptiform discharges. Magnetoencephalography (MEG) is less affected by the skull breach. The postcraniotomy EEG and MEG scans of 20 patients were reviewed by two experienced electroencephalographers. Larger interrater variability was found for EEG as compared with MEG. Review of patients who had postoperative seizures suggested that EEG was more sensitive but less specific than MEG in detecting interictal epileptiform discharges. Furthermore, several instances of sharp waveforms that were difficult to evaluate on EEG were found to be more easily interpretable on MEG. MEG may also help determine whether asymmetries in physiologic rhythms on EEG result from the skull defect or are pathologic. MEG should be considered as an adjunctive study in patients with a breach rhythm for evaluation of interictal epileptiform discharges and cerebral dysfunction.

A moving finite element simulation of a pressure swing adsorption process

A moving finite element method (MFEM) was applied to the simulation of a pressure swing adsorption (PSA) process based on the local equilibrium model. The PSA process studied is the system of air-5A zeolite for enriching oxygen. Four steps of product pressurization, feed, blowdown, and purge are included in this process. Reasonable agreements are obtained when the theoretical results are compared with the experimental data of Matz and Knaebel (1988). By the property of the moving nodes in MFEM and using small weighting factors, a fixed number of nodes was used to simulate this PSA process, in which a sharp concentration wave forms and moves from the feed end of the column to the product end during the feed step and a simple wave moves in the reverse direction during the purge step. The use of small weighting factors is equivalent to the strong action of the penalty function. The effects of the weighting factors and boundary conditions on the implementation of the MFEM are also discussed.

Automatic recognition and quantification of interictal epileptic activity in the human scalp EEG

An attempt was made at using a small computer to recognize and quantify interictal epileptic activity (spikes and sharp waves) in the human scalp EEG. To perform the automatic recognition, the EEG of each channel is broken down into half-waves. A half-wave is characterized by its duration and its amplitude relative to the background activity. A wave is characterized by the durations and amplitudes of its two component half-waves, by the second derivative at its apex measured relative to the background activity, and by the duration and amplitude of the following half-wave. Particular combinations of these parameters were found to characterize spikes and sharp waves and are used for their recognition and quantification. Specific methods are used for the rejection of spike-like or sharp wave-like wave forms such as eye blinks, muscle potentials and sharp alpha activity and were found to perform with a high level of reliability. Interchannel relationships are thoroughly examined to determine areas of maximal epileptogenicity. Sixteen channels can be analyzed in real time. Results are presented in a simple picture containing localizing and quantitative information. Specific questions regarding the time relationships of spikes in different channels can be asked interactively by the user. The system is of potential use in clinical electroencephalography.

Interactive analysis and display of the electroencephalogram (EEG) in real time

The development of fast, relatively inexpensive graphics terminals permits the integration of interactive display with on-line, real time signal analysis in dedicated minicomputer systems. Interactive display in the context of electroencephalogram (EEG) analysis includes: (1) control over form and parameters of an isometric plot using hidden line suppression and floating level; (2) selection of function and transform to graph; and (3) expansion or contraction of coordinate axes and timerscale, from ‘wide angle’ views of the course of several hours of recording of the entire scalp, to ‘telescopic’ blow-ups of the details of two or three seconds of activity in a single channel. The analysis paradigms function on-line and in real time, and incorporate parallel time domain and spectral analyses on data from eight or fewer electrode placements. Spectral estimates of power and simple coherences are typically formed using ensemble averages of non-overlapping one-half to two second periodograms obtained by Fast Fourier Transform. Transient analysis uses heuristic strategies to isolate clinically significant patterns, such as the sharp paroxysmal wave forms associated with the epilepsies. Instrumental and extra-cerebral artifact are partially eliminated by algorithms based upon heuristic criteria. Parameters of spectral and transient analysis are interactively alterable to facilitate varying experimental paradigms. To implement such systems, which can be both compute and I/O bound, it is necessary to optimize systems software. A simple and multitasking executive coordinates program task modules. Memory space and computing time are conserved through extensive use of dynamic buffer allocation and double precision integer arithmetic.

A wide-range linear delay circuit

A wide-range linear delay circuit is described. Such circuits have wide applications. The present circuit, which has excellent temperature stability, employs a compensated bootstrap circuit for generation of a linear ramp waveform and a regenerative Schmitt triggor comparator. The circuit provides good performance and sharp waveforms which may be used for triggering other digital circuits directly.

Effect of chlorpromazine upon epileptic and normal monkeys.

Conclusions1. The rapid intravenous administration of chlorpromazine (2-10 mg/kg) to epileptic and normal monkeys produced prompt profound behavioral changes characterized by hypokinesia, flaccidity, diminished responsiveness, reduced aggressiveness, lethargy and somnolence. 2. High amplitude slow wave activity (2-5 second) became dominant in the EEG up to several hours after intravenous injection of chlorpromazine; epileptic monkeys showed, in addition, increased high amplitude spike and sharp wave forms. 3. Epileptic monkeys under the acute influence of chlorpromazine retained their clinical convulsive responsiveness to intramuscular Met-razol (16 mg/kg or less). Clinical epileptic response to vigorous prodding was not significantly changed. 4. Normal control monkeys under the acute influence of chlorpromazine did not exhibit clinical convulsions and remained refractory to treatment with intramuscular Metrazol (32 mg/kg) and to vigorous prodding stimulation.