Neonatal seizures are common, often require electroencephalographic (EEG) monitoring for diagnosis and management, may be associated with worse neurodevelopmental outcome, and can often be treated with existing anticonvulsants. A neonatal electrographic seizure is defined as a sudden, repetitive, evolving and stereotyped event of abnormal electrographic pattern with amplitude of at least two microvolts and a minimum duration of ten seconds. The diagnosis of neonatal seizures relies heavily on the neurophysiologist’s interpretation of EEG. Consideration of specific criteria for the definition of a neonatal seizure, including seizure duration, location, morphology, evolution, semiology, and overall seizure burden, have utility for both the clinician and researcher. We review the importance of EEG in the diagnosis and management of neonatal seizures, the electrographic characteristics of neonatal seizures, the impact of neonatal seizures on outcome, and tools to aid in the identification of neonatal seizures.
seizures; neonate; electroencephalography; status epilepticus
Dorsolateral frontal lobe seizures often present as a diagnostic challenge. The diverse semiologies may not produce lateralizing or localizing signs, and can appear bizarre and suggest psychogenic events. Unfortunately, scalp EEG and MRI are often unsatisfactory. It is not uncommon that these traditional diagnostic studies are either unhelpful or even misleading. In some cases SPECT and PET imaging can be an effective tool to identify the origin of seizures. However, these techniques and other emerging techniques all have limitations, and new approaches are needed to improve source localization.
Frontal lobe epilepsy; EEG
Infraslow Activity (ISA), Direct Coupled (DC), or Direct Current (DC) are the terms used to describe brain activity that occurs in frequencies below 0.1Hz. ISA amplitude increase is also associated with epilepsy, traumatic brain injuries, strokes, tumors and migraines and has been studied since the early 90’s at the Henry Ford Hospital MEG Laboratory. We have used a DC based MEG system to validate and characterize the ISA from animal models of cortical spreading depression (CSD) thought to be the underlying mechanism of migraine as well as other CSD-like events seen during ischemia, anoxia, and epilepsy. MEG characterizes these slow shifts easier than EEG as there is no attenuation of these signals by the skull. In the current study we report on ISA MEG signals of 12 patients with epilepsy in the pre- and postictal state. In the minutes just prior to the onset of a seizure, large amplitude, ISA MEG waveforms were detected, signaling the onset of the seizure. It is suggested that MEG assessment of ISA, in addition to activity in the conventional frequency band, can at times be useful in the lateralization of epileptic seizures.
Magnetoencephalography (MEG); Electroencephalography (EEG); Ictal activity; Infra Slow Activity (ISA); Direct Coupled (DC); cortical spreading depression (CSD)
In neocortical epilepsy, we showed that the seizure onset defined by ictal high frequency oscillations (HFO: ≥70 Hz) with subsequent evolution into slower frequency activity (i.e., HFOs+) was smaller in spatial distribution than that defined by conventional frequency activity (CFA: 1–70 Hz), and that resection of HFO+ areas resulted in favorable seizure outcome (Modur et al., Epilepsia 2011; 52:1792–1801). This study further investigates ictal broadband EEG in the same cohort of patients by examining the infraslow activity (ISA) including ictal baseline (“DC”) shifts (IBS) and peri-ictal infraslow activity (PISA: 0.02–0.2 Hz). The seizure onset zone (SOZ) had been defined and resected based on HFO+ by a prospectively-defined protocol. We reviewed 11 representative seizures from 6 patients by visual and spectral analyses using appropriate filters and time scales. The HFO seizure onset, in the high gamma or ripple frequency, preceded or followed the IBS closely (<300-ms). The IBS were negative or positive, ~1 mV in amplitude and 2–3 s long. While the HFO+ were always ipsilateral to the surgical hemisphere, the IBS could be ipsilateral or contralateral. Compared to CFA, the HFO+ and IBS were significantly smaller in spatial distribution and likely to be concordant. The PISA consisted of distinct periodic or rhythmic (0.12–0.16 Hz) patterns, poorly concordant with IBS or HFO+. Although not statistically significant, better seizure outcome tended to correlate with smaller SOZs and more complete resection of the HFO+ and IBS contacts. We conclude that IBS, like HFO+, define a smaller SOZ and probably a more accurate epileptogenic zone in neocortical epilepsy.
Seizure; Epilepsy; Surgery; Intracranial; High frequency oscillations; HFO; Infraslow; DC shift; Broadband; EEG
The differential dysfunction of chromatic and achromatic visual pathways in early Parkinson’s disease (PD) was evaluated by means of visual-evoked potentials (VEPs) recorded in 12 patients (mean age 60.1 ± 8.3 years; range 46 to 74 years) in the early stages of PD and not yet undergoing treatment with L-dopa, and in 12 age-matched controls. Visual stimuli were full-field (14 deg) equiluminant red-green (R-G), blue-yellow (B-Y), and black-white (B-W) sinusoidal gratings of two cycles per degree, presented in onset (300 milliseconds) – offset (700 milliseconds) mode, at two contrast (K) levels (90% and 25%). The VEP mean latencies were significantly more delayed in PD patients than in controls for chromatic than for luminance stimuli, in particular for B-Y stimuli of low contrast (K90%: B-W =6.6 milliseconds, R-G =3.34 milliseconds, B-Y =15.48 milliseconds; K25%: B-W =7.8 milliseconds, R-G =14.8 milliseconds, B-Y =28.9). Latencies of chromatic VEPs were more variable that achromatic VEP latencies in both normal subjects and PD patients. Therefore, the frequency of latency abnormalities (within 30%) was not significantly different for the three visual stimuli. Our results show that, in addition to achromatic VEPs, chromatic VEPs are impaired in early PD patients not yet undergoing L-dopa therapy, indicating an acquired color deficiency in these patients. The greater delay for the B-Y VEPs suggests a higher vulnerability of visual blue-cone pathway in the early stages of the disease. However, the overall sensitivity of chromatic VEPs in detecting early visual impairment in PD is comparable with that of achromatic VEPs.
Chromatic contrast; VEPs; Parkinson’s disease; Parvocellular; Koniocellular; Magnocellular system
Magnetoencephalography (MEG) non-invasively measures the magnetic fields produced by the brain. Pertinent research articles from 1993 to 2009 that measured spontaneous, whole-head MEG activity in schizophrenic patients were reviewed. Data on localization of oscillatory activity and correlation of these findings with psychotic symptoms are summarized. While the variety of measures used by different research groups makes a quantitative meta-analysis difficult, it appears that MEG activity in patients may exhibit identifiable patterns, defined by topographic organization and frequency band. Specifically, 11 of the 12 studies showed increased theta (4–8 Hz) and delta (1–4 Hz) band oscillations in the temporal lobes of patients; of the 10 studies that examined the relationship between oscillatory activity and symptomatology, 8 found a positive correlation between temporal lobe theta activity and positive schizophrenic symptoms. Abnormally high frontal delta activity was not seen. These findings are analyzed in comparison to the EEG literature on schizophrenics, and possible confounds (e.g., medication effects) are discussed. In the future, MEG might be used to assist in diagnosis, or might be fruitfully used in conjunction with new neuroscience research approaches such as computational modeling, which may be able to link oscillatory activity and cellular-level pathology.
magnetoencephalography; schizophrenia; resting state networks; oscillations; positive symptoms; antipsychotic agents
Periodic limb movements (PLMs) and obstructive sleep apnea (OSA) may present as overlapping conditions. This study investigated the occurrence of PLM during continuous positive airway pressure (CPAP) titration, with the hypothesis that the presence of PLM during CPAP represented “unmasking” of a coexisting sleep disorder.
A total of 78 polysomnographic recordings in 39 OSA subjects with an hourly PLM index ≥5 during CPAP application were evaluated.
Application of CPAP significantly improved sleep architecture without change in the PLM index when compared with baseline. The PLM indices and PLM arousal indices were linearly correlated during both nights (r = 0.553, P < 0.01; r = 0.548, P < 0.01, respectively). Eleven subjects with low PLM indices at baseline had greater changes in the PLM index as compared with the sample remainder (P = 0.004). Sixteen subjects with significantly lower PLM indices at baseline required optimal CPAP levels higher than the sample average of 8.2 cm H2O (P = 0.032). These subjects also showed significantly higher median apnea–hypopnea index (AHI) at baseline than the sample remainder (74.4 events per hour [range: 24.2–124.4 events per hour] vs. 22.7 events per hour [range: 8.6–77.4 events per hour], respectively, P < 0.001).
These findings suggest that PLM seen during CPAP titration may be related to a concurrent sleep disorder because of “unmasking” in patients with treated OSA.
Periodic limb movements (PLM); Obstructive sleep apnea (OSA); Continuous positive airway pressure (CPAP); Sleep disorders; Polysomnography
Recent research aims at developing a biomarker to predict antidepressant treatment outcomes in Major Depressive Disorder (MDD). The Antidepressant Treatment Response index (ATRindex) has been correlated with response to antidepressant medication (Leuchter et al., 2009a, 2009b) but has not been assessed in a placebo-controlled trial. EEGs were used to calculate ATR-index for 23 randomized MDD subjects to eight weeks of fluoxetine treatment (FLX) 20 mg (n=12) or placebo (n=11). The 17-item Hamilton Depression Rating Scale (HamD17) assessed symptom severity, while a percent change in HamD17 score, endpoint response (≥ 50% improvement) and remission (HamD17 score ≤ 7) were used to assess ATR-index as a predictor. ATR-index was significantly associated with improvement on FLX (r = .64, p = .01), with a higher mean ATR-index for FLX responders than non-responders (t(10)= −2.07, p=0.03). Receiver Operating Characteristic analysis found a .83 area under the curve (p = .03), for ATR-index as a predictor for FLX, while an optimized ATR-index cutoff of 47.3 yielded 100% sensitivity, 66.7% specificity, 75% PPV and 100% NPV. Importantly, ATR-index did not correlate significantly with placebo outcomes. Results extend ATR-index findings to include predictive validity with fluoxetine, suggesting that this biomarker has specificity for drug effects.
antidepressant medication; placebo response; biomarker; EEG
To compare three methods of localizing the source of epileptiform activity recorded with magnetoencephalography (MEG): equivalent current dipole (ECD), minimum current estimate (MCE), and dynamic statistical parametric mapping (dSPM), and to evaluate the solutions by comparison with clinical symptoms and other electrophysiological and neuroradiological findings.
Fourteen children of 3 to 15 years old were studied. MEG was collected with a whole-head 204-channel helmet-shaped sensor array. We calculated ECDs and made MCE and dSPM movies to estimate the cortical distribution of interictal epileptic discharges (IED) in these patients.
The results for 4 patients with localization related epilepsy (LRE) and 1 patient with Landau-Kleffner Syndrome were consistent among all 3 analysis methods. In the rest of the patients MCE and dSPM suggested multifocal or widespread activity; in these patients the ECD results were so scattered that interpretation of the results was not possible. For 9 patients with LRE and generalized epilepsy, the epileptiform discharges were wide-spread or only slow waves, but dSPM suggested a possible propagation path of the IED.
MCE and dSPM could identify the propagation of epileptiform activity with high temporal resolution. The results of dSPM were more stable because the solutions were less sensitive to background brain activity.
MEG; epilepsy; dynamic statistical parametric mapping; minimum current estimate; minimum norm estimate; equivalent current dipole
The following are “minimum standards” for the routine clinical recording of magnetic evoked fields (MEFs) in all age-groups.
Practicing at minimum standards should not be the goal of a magnetoencephalography (MEG) center but rather a starting level for continued improvement. Minimum standards meet only the most basic responsibilities to the patient and the referring physician.
These minimum standards have been put forth to improve standardization of procedures, to facilitate interchange of recordings and reports among laboratories in the United States, and to confirm the expectations of referring physicians.
Recommendations regarding Laboratory (Center) Environment and Preparation for MEG Recordings are detailed in the American Clinical Magnetoencephalography Society Clinical Practice Guideline (CPG) 1 : Recording and Analysis of Spontaneous Cerebral Activity, except for its EEG aspect that is not considered necessary (although may be helpful in trained hands) for MEFs (presurgical functional brain mapping).
Correct outcome prediction after cardiac arrest in children may improve clinical decision making and family counseling. Various investigators have used EEG to predict outcome with varying success, but one limiting issue is the potential lack of reproducibility of EEG interpretation. Therefore, we aimed to evaluate interobserver agreement using standardized terminology in the interpretation of EEG tracings obtained from critically ill children following cardiac arrest.
3 pediatric neurophysiologists scored 74 EEG samples using standardized categories, terminology, and interpretation rules. Interobserver agreement was evaluated using kappa and intra-class correlation coefficients.
Agreement was substantial for the categories of continuity, burst suppression, sleep architecture, and overall rating. Agreement was moderate for seizure occurrence and inter-ictal epileptiform discharge type. Agreement was fair for inter-ictal epileptiform discharge presence, beta activity, predominant frequency, and fastest frequency. Agreement was slight for maximum voltage and focal slowing presence.
The variability of inter-rater agreement suggests that some EEG features are superior to others for use in a predictive algorithm. Using only reproducible EEG features is needed to ensure the most accurate and consistent predictions. Since even seizure identification had only moderate agreement, studies of non-convulsive seizures in critically ill patients must be conducted and interpreted cautiously.
Electroencephalogram; Interobserver variability; Seizure; Pediatric; Hypoxic Ischemic Encephalopathy; Cardiac Arrest
Theta Burst Stimulation (TBS) protocols have recently emerged as a method to transiently alter cortical excitability in the human brain through repetitive transcranial magnetic stimulation (rTMS). TBS involves applying short trains of stimuli at high frequency repeated at intervals of 200ms. Because rTMS is known to carry a risk of seizures, safety guidelines have been established. TBS has the theoretical potential of conferring an even higher risk of seizure than other rTMS protocols because it delivers high frequency bursts. In light of the recent report of a seizure induced by TBS, the safety of this new protocol deserves consideration. We performed an English language literature search, and reviewed all studies published from May 2004-December 2009 in which TBS was applied. The adverse events were documented and crude risk was calculated. The majority of adverse events attributed to TBS were mild and occurred in 5% of subjects. Based on this review, TBS appears to be a safe and efficacious technique. However, given its novelty, it should be applied with caution. Additionally, this review highlights the need for rigorous documentation of adverse events associated with TBS, as well as intensity dosing studies to assess the seizure risk associated with various stimulation parameters (e.g. frequency, intensity, location).
Theta Burst Stimulation; Safety; Transcranial Magnetic Stimulation; Adverse Events; Risks; Meta-analysis
Microseizures are highly focal low-frequency epileptiform-appearing events recorded from the neocortex of epilepsy patients. Because of their tiny, often submillimeter distribution they may be regarded as a high resolution window into the epileptic process, providing an excellent opportunity to study the fine temporal structure of their origin and spread. A 16 mm2 96 microelectrode array with 400 micron interelectrode spacing was implanted in seven patients undergoing invasive EEG monitoring for medically refractory epilepsy. Seven microdischarge populations were tested for a substantial contribution by volume conduction to the observed waveform amplitudes. Single unit activity was examined for specific evidence of neural activity at multiple sites within the microdischarge fields. We found that microdischarges appear to originate at a highly focal source location, likely within a single cortical macrocolumn, and spread to local and more distant sites via neural propagation.
multichannel extracellular recording; epilepsy; intracranial EEG; epileptiform discharges; microseizures
In the neocortex, neurons participate in epochs of elevated activity, or Up states, during periods of quiescent wakefulness, slow-wave sleep, and general anesthesia. The regulation of firing during and between Up states is of great interest because it can reflect the underlying connectivity and excitability of neurons within the network. Automated analysis of the onset and characteristics of Up state firing across different experiments and conditions requires a robust and accurate method for Up state detection. Using measurements of membrane potential mean and variance calculated from whole-cell recordings of neurons from control and postseizure tissue, the authors have developed such a method. This quantitative and automated method is independent of cell- or condition-dependent variability in underlying noise or tonic firing activity. Using this approach, the authors show that Up state frequency and firing rates are significantly increased in layer 2/3 neocortical neurons 24 hours after chemo-convulsant-induced seizure. Down states in postseizure tissue show greater membrane-potential variance characterized by increased synaptic activity. Previously, the authors have found that postseizure increase in excitability is linked to a gain-of-function in BK channels, and blocking BK channels in vitro and in vivo can decrease excitability and eliminate seizures. Thus, the authors also assessed the effect of BK-channel antagonists on Up state properties in control and postseizure neurons. These data establish a robust and broadly applicable algorithm for Up state detection and analysis, provide a quantitative description of how prior seizures increase spontaneous firing activity in cortical networks, and show how BK-channel antagonists reduce this abnormal activity.
epilepsy; seizure; Up state; BK channels; classification
People aged 90 and older (oldest-old), the fastest growing segment of the United States population, are known to have high rates of spells of all types, including strokes, transient ischemic attacks, and seizures. This study examined the prevalence of EEG abnormalities in 12 physically and cognitively healthy oldest-old (mean age=94) with no history of seizures or spells. Abnormalities were found in 83% of participants: temporal intermittent polymorphic slowing was seen in 67%, background slowing (alpha rhythm <8 Hz) was present in 33%, and temporal intermittent rhythmic delta was found in 17%. The high rates of EEG abnormalities found in these physically and cognitively healthy participants prompt reappraisal of pathological significance in this unique population.
Electroencephalography (EEG); aging; oldest-old; temporal intermittent rhythmic delta activity (TIRDA)
Elderly subjects exhibit declining sleep efficiency parameters with longer time spent awake at night and greater sleep fragmentation. In this paper, we report on the changes in cortical interdependence during sleep stages between 15 middle aged (range: 42-50 years) and 15 elderly (range: 71-86 years) women subjects. Cortical interdependence assessed from EEG signals typically exhibits increasing levels of correlation as human subjects progress from wake to deeper stages of sleep. EEG signals acquired from previously existing polysomnogram data sets were subjected to mutual information (MI) analysis to detect changes in information transmission associated with change in sleep stage and to understand how age affects the interdependence values. We observed a significant reduction in the interdependence between central EEG signals of elderly subjects in NREM and REM stage sleep in comparison to middle-aged subjects (age group effect: elderly vs. middle aged p<0.001, sleep stage effect: p<0.001, interaction effect between age group and sleep stage: p=0.007). A narrow band analysis revealed that the reduction in MI was present in delta, theta and sigma frequencies. These findings suggest that the lowered cortical interdependence in sleep of elderly subjects may indicate independently evolving dynamic neural activities at multiple cortical sites. The loss of synchronization between neural activities during sleep in the elderly may make these women more susceptible to localized disturbances that could lead to frequent arousals.
Age; Sleep; Mutual Information; Interdependence
Develop a method for automatic detection of seizures prior to or immediately after clinical onset using features derived from scalp EEG.
This detection method is patient-specific. It uses recurrent neural networks and a variety of input features. For each patient we trained and optimized the detection algorithm for two cases: 1) during the period immediately preceding seizure onset, and 2) during the period immediately following seizure onset. Continuous scalp EEG recordings (duration 15 – 62 h, median 25 h) from 25 patients, including a total of 86 seizures, were used in this study.
Pre-onset detection was successful in 14 of the 25 patients. For these 14 patients, all of the testing seizures were detected prior to seizure onset with a median pre-onset time of 51 sec and false positive rate was 0.06/h. Post-onset detection had 100% sensitivity, 0.023/hr false positive rate and median delay of 4 sec after onset.
The unique results of this study relate to pre-onset detection.
Our results suggest that reliable pre-onset seizure detection may be achievable for a significant subset of epilepsy patients without use of invasive electrodes.
Epilepsy; Early Seizure Detection; Recurrent Neural Networks; Scalp EEG
Eight right-handed subjects were asked to silently generate a verb to a visual stimulus while the magnetic flux normal to the scalp surface was recorded with a whole-head neuromagnetometer. The spatiotemporal patterns of activation in lateral occipital, inferior parietal, superior temporal, basal temporal, and inferior frontal cortices were estimated using minimum estimation, a distributed source analysis methodology. Although there was significant variability among subjects, averaged data indicated that latencies of peak activation in these regions of interest progressed from posterior to anterior. Peak latencies were earliest in lateral occipital cortex and latest in pars opercularis and pars triangularis in the inferior frontal gyrus. Lateralization of activation was strongest in pars opercularis, which is part of classical Broca’s area, with activation being stronger in this area within the left hemisphere in every subject. Results provide support for the use of magnetoencephalography in conjunction with MNE analysis for the purpose of lateralizing and localizing language-specific activation in frontal areas as well as the study of the spatiotemporal parameters of brain activation associated with cognitive function.
Magnetoencephalography; Cognition; Naming
EEGs are widely used to detect interictal epileptiform discharges (IEDs) in patients with a known history of seizures. However, prior studies have not found a consistent association between the presence or frequency of IEDs and clinical epilepsy severity, possibly because of differences in subject characteristics and recording techniques. We sought to investigate this relationship in a population and setting reflective of the most common clinical usage.
We analyzed EEGs and clinical records of all consenting patients with a history of at least two presumed focal-onset seizures who presented for routine EEG recording over one year’s time in an academic neurophysiology laboratory (n = 129).
Despite adequate statistical power, we did not find an association between the presence or absence of IEDs or IED frequency and the most recently determined seizure frequency (median 4 per year). A higher IED incidence was seen in subjects with longer epilepsy duration (p = 0.04). Neither IED incidence nor frequency (median 10.0 per hour) correlated with age or antiepileptic drug use.
Our results differ from those of some prior studies, most of which focused on more narrow subject populations, suggesting that the patient’s clinical circumstances must be taken into account before assuming the utility of IEDs on routine EEG in predicting epilepsy severity.
Electroencephalography (EEG); interictal spikes; seizure frequency
This study investigated the effects of acute psychosocial stress on trapezius single motor unit discharge behaviors. Twenty-one healthy women performed feedback-controlled isometric contractions under conditions of low and high psychosocial stress in the same experimental session. Psychosocial stress was manipulated using a verbal math task combined with social evaluative threat which significantly increased perceived anxiety, heart rate, and blood pressure (P<0.001). Motor unit discharge behaviors including the threshold and discharge rate at recruitment (7.7 (5.7) %MVC and 7.3 (6.8) pps, P>0.121, N=103) and derecruitment (6.0(4.4) %MVC and 6.5(4.1) pps, P>0.223, N=99), the mean (11.3 (2.3) pps, P=0.309, N=106) and variability (2.5 (0.91) pps, P=0.958, N=106) of discharge rate, and the proportion of motor units exhibiting double discharges (21%, P=0.446) did not change across stress conditions. Discharge rate modulation with changes in contraction intensity was highly variable and similar across stress conditions (P>0.308, N=89). Rate-rate modulation of concurrently active motor units was also highly variable (r=−0.84–1.00, N=75). Estimates of ΔF for motor unit pairs with rate-rate modulation ≥0.7 were positive and similar across stress conditions (4.7(2.0) pps, P=0.405, N=16). Results indicate that acute psychosocial stress does not alter trapezius motor unit discharge behaviors during a precisely controlled motor task in healthy women.
Motoneuron; Anxiety; Discharge rate modulation; Intrinsic activation; EMG; Muscle activation
In 9 patients with essential tremor (14 thalami), we varied frequency, voltage, and pulsewidth of thalamic deep brain stimulation (DBS), and quantified postural tremor. Low frequency stimulation aggravated tremor; the effect increased with increasing voltage. High frequency stimulation had a U-shaped relation to voltage, with minimum tremor at an optimal voltage characteristic of the individual thalamus and increases in voltage beyond the optimum reduced tremor suppression.
Based on the hypothesis that tremor response to DBS resulted from two competing processes, we successfully modeled the relationship of tremor to voltage and frequency of stimulation using a mathematical model. The optimum voltage predicted by the model agreed with the empirically measured value. Moreover, the model made accurate predictions at high stimulation frequency based on measurements made at low stimulation frequency.
Our results indicate there is an optimal voltage for tremor suppression by thalamic DBS in most patients with ET. The optimum varies across patients, and this is related to electrode position. A mathematical model based on ‘competing processes’ successfully predicts optimum voltage in individual patients. This supports a competing processes model of DBS effects.
deep brain stimulation; movement disorders; essential tremor; surgery; thalamus; thalamic stimulation
The authors report the use of dense two-dimensional microelectrode array recordings to characterize fine resolution electrocortical activity (“μEEG”) in epileptogenic human cortex. A 16-mm2 96 microelectrode array with 400-μm interelectrode spacing was implanted in five patients undergoing invasive EEG monitoring for medically refractory epilepsy. High spatial resolution data from the array were analyzed in conjunction with simultaneously acquired data from standard intracranial electrode grids and strips. μEEG recorded from within the epileptogenic zone demonstrates discharges resembling both interictal epileptiform activity (“microdischarges”) and electrographic seizures (“microseizures”) but confined to cortical regions as small as 200 μm2. In two patients, this activity appeared to be involved in the initiation or propagation of electrographic seizures. The authors hypothesize that microdischarges and microseizures are generated by small cortical domains that form the substrate of epileptogenic cortex and play important roles in seizure initiation and propagation.
Multichannel extracellular recording; Epilepsy; Intracranial EEG; Epileptiform EEG discharges
The regularity of EEG signals was compared between middle-aged (47.2 ± 2.0 yrs) and elderly (78.4 ± 3.8 yrs) female subjects in Wake (W), NREM stages 2 and 3 (S2, S3), and REM. Signals from C3A2 leads of healthy normal subjects, acquired from polysomnograms obtained from the Sleep Heart Health Study, were analyzed using both Sample Entropy (SaEn) and power spectral analysis (delta, theta, alpha, and beta frequency band powers). SaEn changed systematically and significantly (p<0.001) with sleep state in both age groups, following the relationships W > REM > S2 > S3. SaEn was found to be negatively correlated with delta power and positively correlated with beta power. Small changes in SaEn appear to reflect changes in spectral content rather than changes in regularity of the signal. A better predictor of SaEn than the frequency band powers was the logarithm of the power ratio (alpha+beta)/(delta+theta). Thus, SaEn appears to reflect the balance between sleep-promoting and alertness-promoting mechanisms. SaEn of the elderly was larger than that of middle-aged subjects in S2 (p=0.029) and REM (p=0.001), suggesting that cortical state is shifted towards alertness in elderly subjects in these sleep states compared to middle-aged.
This paper describes the design and test results of a 3-stage automated system for neonatal EEG seizure detection. Stage I of the system is the initial detection stage, and identifies overlapping 5-s segments of suspected seizure activity in each EEG channel. In Stage II, the detected segments from Stage I are spatiotemporally clustered to produce multi-channel candidate seizures. In Stage III, the candidate seizures are processed further using measures of quality and context-based rules to eliminate false candidates. False candidates due to artifacts and commonly occurring EEG background patterns such as bifrontal delta activity are also rejected. Seizures at least 10 s in duration are considered for reporting results.
The testing data consisted of recordings of 28 seizure subjects (34 hrs of data) and 48 non-seizure subjects (87 hrs of data) obtained in the neonatal intensive care unit. The data were not edited to remove artifacts and were identical in every way to data normally processed visually. The system was able to detect seizures of widely varying morphology with an average detection sensitivity of almost 80% and a subject sensitivity of 96%, in comparison to a team of clinical neurophysiologists who had scored the same recordings. The average false detection rate obtained in non-seizure subjects was 0.74 per hr.
EEG; neonatal; epileptic; seizure; detection; automated
It is desirable to estimate both location and extent information of epileptogenic zones from noninvasive EEG. In the present study, we use a subspace source localization method, i.e. FINE, combined with a local thresholding technique to achieve such tasks. We have evaluated the performance of this method in interictal spikes from three pediatric patients with medically intractable partial epilepsy. The present results suggest that the thresholded subspace correlation, which is obtained from FINE scanning, is a favorable marker, which implies the extents of current sources associated with epileptic activities. Our findings were validated through comparison to invasive ECoG recordings during interictal spikes. The surgical resections in these three patients are well correlated with the epileptogenic zones identified from both EEG sources and ECoG potential distributions. The value of the proposed noninvasive technique for estimating epileptiform activity was supported by satisfactory surgery outcomes.
source localization; extent; EEG; ECoG; FINE; epilepsy; interictal; MRI; surgical outcome