2-second Epochs Research Articles

Heterogeneous Recurrence Analysis of imaged-EEG for Spatio-Temporal Epileptic Seizure Detection.

Epilepsy is known as a heterogeneous neurological disorder affecting 1 to 3 percent of the worldwide population. Epileptic seizures occur when brain cells feature abnormal synchronized recurrent activities. In this study, Heterogeneous Recurrence Analysis (HRA) is utilized to investigate seizure phenomena and to develop a spatio-temporal seizure detection algorithm. Using recurrence characteristics of multichannel scalp electroencephalography (EEG) signals we tried to model seizures by frequent feature values in neighboring channels. For this aim, some elementary features in time, frequency, and statistical domain are extracted from 2-second epochs and used to make imaged-EEGs. Each recording's channel-set provides the ground rule for placing feature values in the specified pixels in the imaged-EEGs. These images are then fed to the HRA algorithm to extract heterogeneous recurrence features in each region of the image. Despite existing methods using each individual channel's characteristics as features for each epoch, this method can provide spatial heterogeneous recurrence information for each region of the image, consequently regions of the brain. Using the HRA method with imaged-EEGs also gives us the ability to extract temporal recurrent features from successive epochs. As a result, groups of channels are considered as one region, and their recurrent behaviors in different traits are quantified as HRA features. Our method was evaluated using two publicly available epileptic EEG datasets recorded from pediatric patients at Boston Children's Hospital (CHB-MIT) and American university of Beirut Medical Center (ABMC). Considering only temporal detection of seizures, the averaged evaluation parameters are 99.6% accuracy, 99.7% sensitivity, 99.4% specificity on 24 patients of CHB-MIT dataset, and 98.5% accuracy, 97.9% sensitivity, 98.5% specificity on 6 patients of ABMC. The results show that the accuracy and specificity of the proposed method are comparable to the best machine learning baseline methods while the sensitivity is better. Besides good classification results, HRA on imaged-EEGs can give us valuable information about the patient's brain lobe/s in which recurrent features are distinctive for seizure detection.

One Minute of EEG Data Provides Sufficient and Reliable Data for Identifying Lewy Body Dementia.

To determine the minimum duration of electroencephalography (EEG) data necessary to differentiate EEG features of Lewy body dementia (LBD), that is, dementia with Lewy bodies and Parkinson disease dementia, from non-LBD patients, that is, Alzheimer disease and Parkinson disease. We performed quantitative EEG analysis for 16 LBD and 14 non-LBD patients. After artifact removal, a fast Fourier transform was performed on 90, 60, and thirty 2-second epochs to derive dominant frequency; dominant frequency variability; and dominant frequency prevalence. In LBD patients, there were no significant differences in EEG features derived from 90, 60, and thirty 2-second epochs (all P >0.05). There were no significant differences in EEG features derived from 3 different groups of thirty 2-second epochs (all P >0.05). When analyzing EEG features derived from ninety 2-second epochs, we found that LBD had significantly reduced dominant frequency, reduced dominant frequency variability, and reduced dominant frequency prevalence alpha compared with the non-LBD group (all P <0.05). These same differences were observed between the LBD and non-LBD groups when analyzing thirty 2-second epochs. There were no differences in EEG features derived from 1 minute versus 3 minutes of EEG data, and both durations of EEG data equally differentiated LBD from non-LBD.

Common patterns of EEG reactivity in post-anoxic coma identified by quantitative analyses

ObjectiveDescription of typical kinds of EEG reactivity (EEG-R) in post-anoxic coma using a quantitative method. MethodsStudy of 101 out-of-hospital cardiac arrest patients, 71 with good outcome (cerebral performance category scale ≤ 2). EEG was recorded 12–24 hours after cardiac arrest and four noxious, one auditory, and one visual stimulation were applied for 30 seconds each. Individual reference intervals for the power in the delta, theta, alpha, and beta bands were calculated based on six 2-second resting epochs just prior to stimulations. EEG-R in consecutive 2-second epochs after stimulation was expressed in Z-scores. ResultsEEG-R occurred roughly equally frequent as an increase or as a decrease in EEG activity. Sternal rub and sound stimulation were most provocative with the most pronounced changes as an increase in delta activity 4.5–8.5 seconds after stimulation and a decrease in theta activity 0.5–4.5 seconds after stimulation. These parameters predicted good outcome with an AUC of 0.852 (95 % CI: 0.771–0.932). ConclusionsQuantitative EEG-R is a feasible method for identification of common types of reactivity, for evaluation of stimulation methods, and for prognostication. SignificanceThis method provides an objective measure of EEG-R revealing knowledge about the nature of EEG-R and its use as a diagnostic tool.

Diagnosis of Alzheimer's disease and Mild Cognitive Impairment using EEG and Recurrent Neural Networks.

Alzheimer's disease (AD) is the main cause of dementia and Mild cognitive impairment (MCI) is a prodromal stage of AD whose early detection is considered crucial as it can contribute in slowing the progression of AD. In our study we attempted to classify a subject into AD, MCI, or Healthy Control (HC) groups with the use of electroencephalogram (EEG) data. Due to the time-series nature of EEG we exper-imented with the powerful recurrent neural network (RNN) classifiers and more specifically with models including basic or bidirectional Long Short-Term Memory (LSTM) modules. The EEG signals from 17 channels were preprocessed using a 0.1-32 Hz band-pass filter and then segmented into 2-second epochs during which, the subject had closed eyes. Finally, on each segment Fast Fourier Transform (FFT) was applied. To evaluate our models we studied four different classification problems: problem 1: separating subject into three classes (HC, MCI, AD) and problems 2-4: pairwise classifications AD vs. MCI, AD vs. HC and MCI vs. HC. For each problem we employed two different cross-validation approaches ( a) by segment and (b) by patient. In the first one, segments from a subject EEG may exist in both training and validations set, while in the second one, all the EEG segments of a subject can only exist in either the training or the validation set. In the AD-MCI-HC classification we achieved an accuracy of 99% by segment cross-validation, which was an improvement to earlier studies that utilized recurrent neural network models. In the pairwise classification problems we achieved over 90% accuracy by segment and over 80% by subject.

Sex differences in resting EEG in healthy young adults

Resting EEG, measured in eyes-closed (EC) and eyes-open (EO) states, can provide insight into behavioural differences between groups. Surprisingly, differences in resting EEG between females and males have not been investigated systematically in previous literature. The present study utilised the four traditional EEG bands to confirm their baseline EC topographies and reactivity (EO minus EC) across groups, to clarify topographical differences between sexes, and to confirm alpha as a measure of arousal. Participants were eighty healthy young adults (40 female), with a mean age of 20.4 (range 18–26) years. Continuous resting EEG was recorded from 30 scalp sites during three 2-minute conditions (EO1, EC, EO2), and EOG-corrected. Data from each condition were divided into 60 sequential 2-second epochs. Accepted artefact-free epochs were Fourier Transformed, and absolute amplitudes in the delta (0.5–3.5 Hz), theta (4.0–7.5 Hz), alpha (8.0–13.0 Hz), and beta (13.5–29.5 Hz) bands were calculated. Across groups in EC, significant topographical differences were found between the band amplitudes, broadly compatible with previous reports. Females had greater overall amplitudes in delta, alpha and beta, enhanced midline activity in theta, and parietal and midline activity in the alpha and beta bands. From EC to EO, reactivity was apparent across the bands as significant reductions, particularly in the parietal region. For females compared to males, the reduction in parietal midline delta and theta, parietal alpha and parietal midline beta was significantly larger. Additionally, across groups, alpha activity was confirmed as an inverse measure of arousal. These findings indicate significant differences in neuronal activity between young adult females and males, and help our interpretation of alpha changes.

Using Deep Convolutional Neural Networks to Develop the Next Generation of Sensors for Interpreting Real World EEG Signals Part 2: Developing Sensors for Vigilance Detection

Using Deep Convolutional Neural Networks to Develop the Next Generation of Sensors for Interpreting Real World EEG Signals Part 2: Developing Sensors for Vigilance Detection

Altered brain functional connectivity induced by physical exercise may improve neuropsychological functions in patients with benign epilepsy

ObjectiveThe objective of this study was to elucidate alteration in functional connectivity (FC) in patients with benign epilepsy with centrotemporal spikes (BECTS) as induced by physical exercise therapy and their correlation to the neuropsychological (NP) functions. MethodsWe analyzed 115 artifact- and spike-free 2-second epochs extracted from resting state EEG recordings before and after 5weeks of physical exercise in eight patients with BECTS. The exact Low Resolution Electromagnetic Tomography (eLORETA) was used for source reconstruction. We evaluated the cortical current source density (CSD) power across five different frequency bands (delta, theta, alpha, beta, and gamma). Altered FC between 34 regions of interests (ROIs) was then examined using lagged phase synchronization (LPS) method. We further investigated the correlation between the altered FC measures and the changes in NP test scores. ResultsWe observed changes in CSD power following the exercise for all frequency bands and statistically significant increases in the right temporal region for the alpha band. There were a number of altered FC between the cortical ROIs in all frequency bands of interest. Furthermore, significant correlations were observed between FC measures and NP test scores at theta and alpha bands. ConclusionThe increased localization power at alpha band may be an indication of the positive impact of exercise in patients with BECTS. Frequency band-specific alterations in FC among cortical regions were associated with the modulation of cognitive and NP functions. The significant correlation between FC and NP tests suggests that physical exercise may mitigate the severity of BECTS, thereby enhancing NP function.

An automated sleep-state classification algorithm for quantifying sleep timing and sleep-dependent dynamics of electroencephalographic and cerebral metabolic parameters.

IntroductionRodent sleep research uses electroencephalography (EEG) and electromyography (EMG) to determine the sleep state of an animal at any given time. EEG and EMG signals, typically sampled at >100 Hz, are segmented arbitrarily into epochs of equal duration (usually 2–10 seconds), and each epoch is scored as wake, slow-wave sleep (SWS), or rapid-eye-movement sleep (REMS), on the basis of visual inspection. Automated state scoring can minimize the burden associated with state and thereby facilitate the use of shorter epoch durations.MethodsWe developed a semiautomated state-scoring procedure that uses a combination of principal component analysis and naïve Bayes classification, with the EEG and EMG as inputs. We validated this algorithm against human-scored sleep-state scoring of data from C57BL/6J and BALB/CJ mice. We then applied a general homeostatic model to characterize the state-dependent dynamics of sleep slow-wave activity and cerebral glycolytic flux, measured as lactate concentration.ResultsMore than 89% of epochs scored as wake or SWS by the human were scored as the same state by the machine, whether scoring in 2-second or 10-second epochs. The majority of epochs scored as REMS by the human were also scored as REMS by the machine. However, of epochs scored as REMS by the human, more than 10% were scored as SWS by the machine and 18 (10-second epochs) to 28% (2-second epochs) were scored as wake. These biases were not strain-specific, as strain differences in sleep-state timing relative to the light/dark cycle, EEG power spectral profiles, and the homeostatic dynamics of both slow waves and lactate were detected equally effectively with the automated method or the manual scoring method. Error associated with mathematical modeling of temporal dynamics of both EEG slow-wave activity and cerebral lactate either did not differ significantly when state scoring was done with automated versus visual scoring, or was reduced with automated state scoring relative to manual classification.ConclusionsMachine scoring is as effective as human scoring in detecting experimental effects in rodent sleep studies. Automated scoring is an efficient alternative to visual inspection in studies of strain differences in sleep and the temporal dynamics of sleep-related physiological parameters.

Physical Activity Assessment Using Different Accelerometer Epoch Lengths During A Low-intensity Ballroom Dance Class

Until recently accelerometry data has been commonly collected using 1-minute sampling intervals (epochs). However, 1-minute epochs may misclassify bouts of (in)activity when compared to more intermittent assessment (e.g. 2-second epochs). PURPOSE: To evaluate variability in physical activity intensity levels using different epoch lengths during a low intensity community dance programme. METHOD: Subjects were 66, mostly senior, adults with a self-assessed status of being physically inactive, who participated in a 2-hour beginners ballroom dance class. During class, physical activity was measured using an Actigraph GT1M accelerometer, set at 2-second epochs. Later, activity counts were transformed into 4, 6, 10, 20, 30 and 60-second epochs. Time spent in sedentary, light and moderate-to-vigorous (MTV) activity was calculated, using adjusted intensity thresholds for each epoch based on counts per minute values of <200, 200-1952 and >1952, respectively. RESULTS: Using 2-second epochs, participants spent 142 ± 9 mins, 32 ± 7 mins and 6 ± 3 mins of class time in sedentary, light and MTV physical activity, respectively. However, sedentary activity based on 4, 6, 10, 20, 30 and 60-second epochs underestimated totals by 5, 7, 10, 14, 17 and 20 mins, respectively. In contrast, time spent in light activity was overestimated by 5, 7, 10, 14, 18 and 22 mins when applying the same epoch periods. Considering MTV, time spent was underestimated by <1 min using 4, 6 and 10-second epochs, and by 1-2 mins using 20, 30 and 60-second epochs. All differences were statistically significant (p<0.01). CONCLUSION: In this case, where a large proportion of time was spent in sedentary and low intensity activity, it is unlikely that the differences obtained for time spent in MTV activity using varying epoch lengths are of biological significance. However, during low intensity activity evaluation, more sensitive (short duration) epochs may provide more accurate estimations. Further research is required to investigate the effect of different epoch lengths when assessing activity changes over time.

Effects of L-Arginine on Electrical Activity in Rats Subjected to Cerebral Ischemia-Reperfusion

Event Abstract Back to Event Effects of L-Arginine on Electrical Activity in Rats Subjected to Cerebral Ischemia-Reperfusion D. Tekin1, Asli Zengin1*, R.B Yildiz1, C. Kayacilar1, A. Nurten1 and I. Kara1 1 Istanbul University, Turkey Nitric oxide (NO) is an important endogenous vasodilatator, which has a variety of physiological and pathological effects in biological system. NO acts as an arterial vasodilator, synthesized from L-arginine by the enzyme nitric oxide synthase, is a biological mediator that facilitates perfusion to affected areas during ischemia-reperfusion (I/R). In present study, we investigated the effects of L-arginine on electrical activity of the hippocampal CA1 areas in rats subjected to cerebral I/R. Male Wistar albino rats, anaesthetized with thiopental (50 mg/kg i.p.), were implanted with electrodes in CA1 areas in stereotaxic apparatus bilaterally. One week after operation, continuous EEG recordings were taken under anesthesia for five minutes. Animals were divided into two groups as saline treated control group (n=6) and L-arginine treated (30 mg/kg i.p.) L-arginine group (n=6). One day after injection, bilateral carotid arteries of all animals were clamped. Thirty minutes after occlusion, clamps were re-opened and EEG recordings were taken in following ten minutes. Continuous EEG recordings were divided into 2-second epochs and analyzed by averaged frequency spectra (0.5-50 Hz) then two tailed paired Student’s t-test was applied. In control group animals, I/R induced the increase in amplitude of low frequency bands and decrease in amplitudes of high frequency bands in CA1 regions significantly compared to basal values. In L-arginine group animals, the electrical activities of CA1 regions in I/R have similar effects to control group animals. This study showed that acute treatment of 30 mg/kg L-arginine, before to the rats subjected to I/R, has no protective effects on electrical activity on hippocampal CA1 regions. Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Animal Models of Cognition Citation: Tekin D, Zengin A, Yildiz R, Kayacilar C, Nurten A and Kara I (2008). Effects of L-Arginine on Electrical Activity in Rats Subjected to Cerebral Ischemia-Reperfusion. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.082 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Dec 2008; Published Online: 02 Dec 2008. * Correspondence: Asli Zengin, Istanbul University, Istanbul, Turkey, aslizenginn@yahoo.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers D. Tekin Asli Zengin R.B Yildiz C. Kayacilar A. Nurten I. Kara Google D. Tekin Asli Zengin R.B Yildiz C. Kayacilar A. Nurten I. Kara Google Scholar D. Tekin Asli Zengin R.B Yildiz C. Kayacilar A. Nurten I. Kara PubMed D. Tekin Asli Zengin R.B Yildiz C. Kayacilar A. Nurten I. Kara Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The Electrical Activity of CA1 Areas in Acutely 7-Nitroindazole Treated Rats in Ischemia-Reperfusion

Event Abstract Back to Event The Electrical Activity of CA1 Areas in Acutely 7-Nitroindazole Treated Rats in Ischemia-Reperfusion Asli Zengin1*, D. Tekin1, C. Kayacilar1, R.B Yildiz1, A. Nurten1 and I. Kara1 1 Istanbul University, Turkey Nitric oxide (NO), produced by nitric oxide synthase (NOS), is an important endogenous vasodilatator. In this study we investigated the effects of 7-nitrindazole (7-NI), a NOS inhibitor, to improved our understanding of NO physiology by investigating electrical activity on hippocampal CA1 regions in rats subjected to cerebral ischemia-reperfusion (I/R). Male Wistar albino rats, anaesthetized with thiopental (50 mg/kg i.p.), were implanted with bilateral electrodes in CA1 areas in stereotaxic apparatus. One week after operation, continuous EEG recordings were taken under anesthesia for five minutes. Then animals were randomly divided into two groups as saline treated control group (n=6) and 50 mg/kg 7-NI treated 7-NI group (n=6). One day after injection, bilateral carotid arteries of all animals were clamped. Thirty minutes after occlusion, clamps were re-opened and EEG recordings were taken in following ten minutes. Continuous EEG recordings were divided into 2-second epochs and analyzed by averaged frequency spectra (0.5-50 Hz), then two tailed paired Student’s t-test was applied. In control group animals, I/R induced the increase in amplitudes of low frequency bands and decrease in amplitudes of high frequency bands in CA1 regions significantly compared to basal values. In 7-NI group animals, the amplitudes of only high frequency bands were significantly decreased in CA1 areas. This study showed that acute treatment with 50 mg/kg 7-NI, before the rats were subjected to I/R, has protective effects on electrical activity on hippocampal CA1 areas in low and high (30 Hz and up) frequency bands. Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Animal Models of Cognition Citation: Zengin A, Tekin D, Kayacilar C, Yildiz R, Nurten A and Kara I (2008). The Electrical Activity of CA1 Areas in Acutely 7-Nitroindazole Treated Rats in Ischemia-Reperfusion. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.083 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Dec 2008; Published Online: 02 Dec 2008. * Correspondence: Asli Zengin, Istanbul University, Istanbul, Turkey, aslizenginn@yahoo.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Asli Zengin D. Tekin C. Kayacilar R.B Yildiz A. Nurten I. Kara Google Asli Zengin D. Tekin C. Kayacilar R.B Yildiz A. Nurten I. Kara Google Scholar Asli Zengin D. Tekin C. Kayacilar R.B Yildiz A. Nurten I. Kara PubMed Asli Zengin D. Tekin C. Kayacilar R.B Yildiz A. Nurten I. Kara Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of averaging data series on the electroencephalographic response to noxious visceral stimulation in isoflurane-anaesthetized dogs

The effects of averaging epochs on electroencephalographic (EEG) responses to visceral stimulation has been determined in seven isoflurane-anaesthetized dogs. Quantitative EEG variables including 80% spectral edge frequency (SEF80), median frequency (MF), relative power in the δ, θ, α, β band and power band ratios ( θ/ δ, α/ δ, β/ δ) were recorded over 1 min before stimulation and during a 1-minute stimulation period. During off-line analysis EEG variables were derived from either single 2-second EEG epochs or as an average from 5, 10, 15 and 30 consecutive 2-second epochs. Noxious stimulation resulted in significant increases in SEF80, MF, α power, β power, α/ δ ratio and β/ δ ratio. The number of variables that were significantly affected as well as the strength of changes as indicated by p-values, however, varied with the number of epochs subjected to averaging. The data suggest that stimulation-induced EEG changes may be more pronounced at lower rather than at higher averaging rates.

Comparison of the distributions of classical and adaptively aligned EEG power spectra

The distributions of eyes-closed resting electroencephalography (EEG) power spectra and their residuals were described and compared using classically averaged and adaptively aligned averaged spectra. Four minutes of eyes-closed resting EEG was available from 69 participants. Spectra were calculated with 0.5-Hz resolution and were analyzed at this level. It was shown that power in the individual 0.5 Hz frequency bins can be considered normally distributed when as few as three or four 2-second epochs of EEG are used in the average. A similar result holds for the residuals. Power at the peak Alpha frequency has quite different statistical behaviour to power at other frequencies and it is considered that power at peak Alpha represents a relatively individuated process that is best measured through aligned averaging. Previous analyses of contrasts in upper and lower alpha bands may be explained in terms of the variability or distribution of the peak Alpha frequency itself.

The localization of epileptic spikes based on spike-triggered fMRI is consistent with EEG source reconstruction

L Lemieux, K Krakow, C Scott*, PJ Allen* and DR Fish Institute of Neurology, UCL, Queen Square, London WCIN 3BG, England *National Hospital for Neurology and Neurosurgery, UCLH, London WClN 3BG, England. Email: llemieux@ion.ucl.ac.uk Introduction The combination of spike-triggered functional magnetic resonance imaging mm and multi-channel electroencephalography (EEG) source reconstruction can provide new insights into the physiological processes underlying epileptiform events. In this study, source reconstruction from 64-channel EEG was used to localize the generators of inter-ia 24cm FOV, 256~256 matrix, 124 1Smm thick slices) was also acquired. 64-channel scalp EEG was also recorded outside the scanner using a QuickCap (NeuroScan, Sterling, VA, USA). For each subject, five 2-second epochs each containing a typical spike were extracted from the recording for source reconstruction. BOLD activation maps were derived from spike-triggered fMRI. The images were processed and analysed using statistical parametric mapping (SPM96) [4]. EEG Source Reconstruction Source reconstruction was performed based on the 64- channel EEG epochs using the Curry 3.0 sow 2) constrained MUSIC dipole scan [5]; 3) constrained current density reconstruction [6]. Comparison of the localisation was carried out by visual inspection using 3D visualisation on a lobar basis. Results The results are summarized in the Table. Significant BOLD activation was obtained in all subjects. Source reconstructions were generally consistent across generator models and individual spikes. The generator was located within, or in the same lobe as, the fMRI activation. The figure illustrates the results for patient #l, a male with a large right &onto-parietal lesion, complex partial and secondary generalised seizures and frequent spikes equipotential at electrodes F8-T4.

Low-level EMFs are transduced like other stimuli

The aims of this study were to test the theory that transduction of low-level electromagnetic fields (EMFs) is mediated like other stimuli, and to determine the false-negative rate of the method used to assess the occurrence of transduction (intra-subject comparison of stimulus and non-stimulus states (ICOS)). A light stimulus was chosen as a basis of comparison because light could be applied and removed at precise time points, similar to the manner in which EMFs were controlled. Subjects exposed to a weak light stimulus during 2-second epochs exhibited alterations in brain electrical activity that were similar to those previously observed in subjects exposed to EMFs. The false-negative rate of the ICOS method was 61%, since it registered an effect in only 39% of the subjects (1128) whereas all subjects were actually aware of the light. In a second group of subjects that were exposed to 0.8 G (1.5 or 10 Hz), 58% (1119) exhibited similar alterations in brain activity, as determined using ICOS. Previous measurements in the same subjects using a different method showed that the EMFs actually affected brain electrical activity in all subjects; consequently, the false-negative rate was 42% when an EMF was used as the stimulus. The results suggested that the post-transduction brain electrical processes in human subjects were similar in the cases of EMF and light stimuli, as hypothesized, and that the high negative rate of the ICOS method (here and in previous studies) was composed partly or entirely of false-negative results.

Model-based analysis of the ECG during early stages of ventricular fibrillation

During the early stages of ventricular fibrillation (VF), identification of the changes in electrocardiographic (ECG) characteristics may be helpful in the determination of defibrillation energy for implantable defibrillators. The hypothesis that the ECG can be quantified by using autoregressive (AR) modeling during VF was tested. Electrocardiograms were recorded for durations of up to 60 seconds of VF in five isolated rabbit hearts. Fourth-order AR parameters of successive 2-second epochs with 50% overlapping of data segments were estimated. At the beginning of VF, mean values of frequency of the first and second poles were 12.5 ± 1.2 Hz and 24.7 ± 1.9 Hz, respectively. During VF, frequencies of these poles decreased. At the end of 60 seconds, pole frequencies were 8.7 ± 1.1 Hz and 21.4 ± 0.8 Hz. Intersubject variability of the frequencies of the poles was found to be low. Maximum standard deviations for the frequencies of the first and second poles were determined to be 1.9 and 2, respectively. Results of this study show that the VF ECG can be modeled by using the AR modeling technique, and it is possible to quantify the changes in the frequency content of the ECG during VF by using this modeling method.

Topographical distribution of absolute alpha-power in the EEG and psychopathology in schizophrenic outpatients.

In 36 schizophrenic outpatients (Research Diagnostic Criteria) under neuroleptic maintenance treatment the EEG was recorded under resting conditions. The absolute alpha-power (7.5-13 Hz) was estimated by Fast Fourier Transform as the mean of 300 2-second epochs for the leads F3/A1, F4/A2, 01/A2 and 02/A2. Two lateralization quotients (anterior, posterior) and two anteriorization quotients (left, right) were calculated from the absolute alpha-power. Clinical status was assessed cross-sectionally with BRPS, GAS and CGI. The main findings are: 1) A linear relationship between the left/right ratio of absolute alpha-power over posterior regions and anxiety/depression--the more the alpha-power is left-lateralized, the higher the anxiety/depression score; 2) a curvilinear, inverted U-shaped relationship between the left/right ratio of absolute alpha-power over posterior regions and the score of schizophrenia-specific symptomatology; 3) the amount of daily neuroleptic dose (mgCPZ) has no impact on EEG-parameters. Results are discussed with respect to hemisphere asymmetry models of psychopathology.