Ultradian characteristics of spontaneous seizure discharges recorded by radio telemetry in man

Brainwaves beyond diagnosis: Wider applications of electroencephalography in idiopathic generalized epilepsy

Electroencephalography (EEG) has long been used as a versatile and noninvasive diagnostic tool in epilepsy. With the advent of digital EEG, more advanced applications of EEG have emerged. Compared with technologically advanced practice in focal epilepsies, the utilization of EEG in idiopathic generalized epilepsy (IGE) has been lagging, often restricted to a simple diagnostic tool. In this narrative review, we provide an overview of broader applications of EEG beyond this narrow scope, discussing how the current clinical and research applications of EEG may potentially be extended to IGE. The current literature, although limited, suggests that EEG can be used in syndromic classification, guiding antiseizure medication therapy, predicting prognosis, unraveling biorhythms, and investigating functional brain connectivity of IGE. We emphasize the need for longer recordings, particularly 24-h ambulatory EEG, to capture discharges reflecting circadian and sleep-wake cycle-associated variations for wider EEG applications in IGE. Finally, we highlight the challenges and limitations of the current body of literature and suggest future directions to encourage and enhance more extensive applications of this potent tool.

Sleep and Epilepsy Link by Plasticity

We aimed to explore the link between NREM sleep and epilepsy. Based on human and experimental data we propose that a sleep-related epileptic transformation of normal neurological networks underlies epileptogenesis. Major childhood epilepsies as medial temporal lobe epilepsy (MTLE), absence epilepsy (AE) and human perisylvian network (PN) epilepsies - made us good models to study. These conditions come from an epileptic transformation of the affected functional systems. This approach allows a system-based taxonomy instead of the outworn generalized-focal classification. MTLE links to the memory-system, where epileptic transformation results in a switch of normal sharp wave-ripples to epileptic spikes and pathological high frequency oscillations, compromising sleep-related memory consolidation. Absence epilepsy (AE) and juvenile myoclonic epilepsy (JME) belong to the corticothalamic system. The burst-firing mode of NREM sleep normally producing sleep-spindles turns to an epileptic working mode ejecting bilateral synchronous spike-waves. There seems to be a progressive transition from AE to JME. Shared absences and similar bilateral synchronous discharges show the belonging of the two conditions, while the continuous age windows - AE affecting schoolchildren, JME the adolescents - and the increased excitability in JME compared to AE supports the notion of progression. In perisylvian network epilepsies - idiopathic focal childhood epilepsies and electrical status epilepticus in sleep including Landau-Kleffner syndrome - centrotemporal spikes turn epileptic, with the potential to cause cognitive impairment. Postinjury epilepsies modeled by the isolated cortex model highlight the shared way of epileptogenesis suggesting the derailment of NREM sleep-related homeostatic plasticity as a common step. NREM sleep provides templates for plasticity derailing to epileptic variants under proper conditions. This sleep-origin explains epileptiform discharges' link and similarity with NREM sleep slow oscillations, spindles and ripples. Normal synaptic plasticity erroneously overgrowing homeostatic processes may derail toward an epileptic working-mode manifesting the involved system's features. The impact of NREM sleep is unclear in epileptogenesis occurring in adolescence and adulthood, when plasticity is lower. The epileptic process interferes with homeostatic synaptic plasticity and may cause cognitive impairment. Its type and degree depends on the affected network's function. We hypothesize a vicious circle between sleep end epilepsy. The epileptic derailment of normal plasticity interferes with sleep cognitive functions. Sleep and epilepsy interconnect by the pathology of plasticity.

Critical slowing down as a biomarker for seizure susceptibility

The human brain has the capacity to rapidly change state, and in epilepsy these state changes can be catastrophic, resulting in loss of consciousness, injury and even death. Theoretical interpretations considering the brain as a dynamical system suggest that prior to a seizure, recorded brain signals may exhibit critical slowing down, a warning signal preceding many critical transitions in dynamical systems. Using long-term intracranial electroencephalography (iEEG) recordings from fourteen patients with focal epilepsy, we monitored key signatures of critical slowing down prior to seizures. The metrics used to detect critical slowing down fluctuated over temporally long scales (hours to days), longer than would be detectable in standard clinical evaluation settings. Seizure risk was associated with a combination of these signals together with epileptiform discharges. These results provide strong validation of theoretical models and demonstrate that critical slowing down is a reliable indicator that could be used in seizure forecasting algorithms.

Critical slowing (associated with increased variance and autocorrelation) can precede critical state transitions. Here, the authors show critical slowing can be used as a marker in seizure forecasting algorithms.

No evidence for critical slowing down prior to human epileptic seizures

There is an ongoing debate whether generic early warning signals for critical transitions exist that can be applied across diverse systems. The human epileptic brain is often considered as a prototypical system, given the devastating and, at times, even life-threatening nature of the extreme event epileptic seizure. More than three decades of international effort has successfully identified predictors of imminent seizures. However, the suitability of typically applied early warning indicators for critical slowing down, namely, variance and lag-1 autocorrelation, for indexing seizure susceptibility is still controversially discussed. Here, we investigated long-term, multichannel recordings of brain dynamics from 28 subjects with epilepsy. Using a surrogate-based evaluation procedure of sensitivity and specificity of time-resolved estimates of early warning indicators, we found no evidence for critical slowing down prior to 105 epileptic seizures.

The effect of antiepileptic drugs on epileptiform discharges in genetic generalized epilepsy: A systematic review

OBJECTIVE

The objective of this study was to evaluate the current evidence regarding the effect of antiepileptic drugs (AEDs) on epileptiform discharge (ED) burden in genetic generalized epilepsy (GGE).

METHODS

We conducted a comprehensive literature search of PubMed, Embase, PsycINFO, and the Web of Science Core Collection databases using the keywords 'genetic generalized epilepsy', 'antiepileptic drugs' and 'epileptiform discharge'. Primary human studies published in English that reported the effect of AEDs on EDs captured on electroencephalogram (EEG) recordings of at least 24 h in duration in patients with GGE were included.

RESULTS

Six studies published between 1984 and 2017, which reported the effect of AEDs on EDs, involving a total of 116 patients with GGE, were analyzed. Our systematic review found a tendency for AEDs to reduce ED density, frequency, cumulative duration, and burst duration in GGE. Furthermore, we found evidence that the AED-mediated reduction in ED burden was associated with improved seizure control and cognitive outcomes.

CONCLUSIONS

Antiepileptic drugs tend to reduce ED burden in GGE, but the significance of this association remains uncertain.

Strong relationship between NREM sleep, epilepsy and plastic functions - A conceptual review on the neurophysiology background

The aim of this review is to summarize and discuss the strong bond between NREM sleep and epilepsy underlain by the shared link and effect on brain plasticity. Beyond the seizure occurrence rate, sleep relatedness may manifest in the enhancement of interictal epileptic discharges (spikes and pathological ripples). The number of the discharges as well as their propagation increase during NREM sleep, unmasking the epileptic network that is hidden during wakefulness. The interictal epileptic discharges associate with different sleep constituents (sleep slow waves, spindling and high frequency oscillations); known to play essential role in memory and learning. We highlight three major groups of epilepsies, in which sleep-related plastic functions suffer an epileptic derailment. In absence epilepsy mainly involving the thalamo-cortical system, sleep spindles transform to generalized spike-wave activity. In mesio-temporal epilepsy affecting the hippocampal declarative memory system, the sharp wave ripples derail to dysfunctional epileptic oscillations (spikes and pathological ripples). Idiopathic childhood epilepsies affecting the perisylvian network may progress to catastrophic status electricus during NREM sleep. In these major epilepsies, NREM sleep has a pivotal role in the development and course of the disorder. Epilepsy is born in-, and exhibits its pathological properties during NREM sleep. Interictal discharges are important causative agents in this process.

Characteristics of Epileptiform Discharge Duration and Interdischarge Interval in Genetic Generalized Epilepsies

We sought to investigate (1) the characteristics of epileptiform discharge (ED) duration and interdischarge interval (IDI) and (2) the influence of vigilance state on the ED duration and IDI in genetic generalized epilepsy (GGE). In a cohort of patients diagnosed with GGE, 24-h ambulatory EEG recordings were performed prospectively. We then tabulated durations, IDI, and vigilance state in relation to all EDs captured on EEGs. We used K-means cluster analysis and finite mixture modeling to quantify and characterize the groups of ED duration and IDI. To investigate the influence of sleep, we calculated the mean, median, and SEM in each population from all subjects for sleep state and wakefulness separately, followed by the Kruskal–Wallis test to compare the groups. We analyzed 4,679 EDs and corresponding IDI from 23 abnormal 24-h ambulatory EEGs. Our analysis defined two populations of ED durations and IDI: short and long. In all populations, both ED durations and IDI were significantly longer in wakefulness. Our results highlight different characteristics of ED populations in GGE and the influence by the sleep–wake cycle.

Temporal patterns of epileptiform discharges in genetic generalized epilepsies

OBJECTIVE

We sought to investigate the temporal patterns and sleep-wake cycle-related epileptiform discharges (EDs) in genetic generalized epilepsies (GGEs).

METHODS

We studied 24-hour ambulatory electroencephalography (EEG) recordings of patients with GGE, diagnosed and classified according to the International League against Epilepsy criteria. We manually coded the type of discharge, time of occurrence, duration, and arousal state of each ED. We employed mixed effects Poisson regression modeling to study the temporal distribution of epileptiform discharges. Additionally, we used multinomial regression analysis to explore the significance of the relationship between different states of arousal and types of epileptiform discharges.

RESULTS

We analyzed 6923 EDs from 105 abnormal 24-hour EEGs. Mixed effects Poisson regression analysis demonstrated significant changes in ED counts across time blocks. This distribution was largely influenced by the state of arousal. Generalized fragments (duration<2s) and focal discharges were more frequent during non-REM sleep while paroxysms (duration≥2s) were more frequent in wakefulness. Overall, 67% of epileptiform discharges occurred in non-REM sleep and only 33% occurred in wakefulness. Twenty-four patients (23%) had ED exclusively in sleep. Epileptiform discharges peaked from 23:00 through 07:00h.

SIGNIFICANCE

There is a time-of-day dependency of ED with a significant influence exerted by the state of arousal. Our observations suggest that the generation of epileptiform discharges is not a random process but is the result of complex interactions among biological rhythms such as the sleep-wake cycle and the intrinsic circadian pacemaker. High density of ED in sleep suggests that 24-hour EEG recording with the capture of natural sleep may be more useful than routine EEG to diagnose GGE.

Human focal seizures are characterized by populations of fixed duration and interval

OBJECTIVE

We report on a quantitative analysis of data from a study that acquired continuous long-term ambulatory human electroencephalography (EEG) data over extended periods. The objectives were to examine the seizure duration and interseizure interval (ISI), their relationship to each other, and the effect of these features on the clinical manifestation of events.

METHODS

Chronic ambulatory intracranial EEG data acquired for the purpose of seizure prediction were analyzed and annotated. A detection algorithm identified potential seizure activity, which was manually confirmed. Events were classified as clinically corroborated, electroencephalographically identical but not clinically corroborated, or subclinical. K-means cluster analysis supplemented by finite mixture modeling was used to locate groupings of seizure duration and ISI.

RESULTS

Quantitative analyses confirmed well-resolved groups of seizure duration and ISIs, which were either mono-modal or multimodal, and highly subject specific. Subjects with a single population of seizures were linked to improved seizure prediction outcomes. There was a complex relationship between clinically manifest seizures, seizure duration, and interval.

SIGNIFICANCE

These data represent the first opportunity to reliably investigate the statistics of seizure occurrence in a realistic, long-term setting. The presence of distinct duration groups implies that the evolution of seizures follows a predetermined course. Patterns of seizure activity showed considerable variation between individuals, but were highly predictable within individuals. This finding indicates seizure dynamics are characterized by subject-specific time scales; therefore, temporal distributions of seizures should also be interpreted on an individual level. Identification of duration and interval subgroups may provide a new avenue for improving seizure prediction.

Are Absence Epilepsy and Nocturnal Frontal Lobe Epilepsy System Epilepsies of the Sleep/Wake System?

System epilepsy is an emerging concept interpreting major nonlesional epilepsies as epileptic dysfunctions of physiological systems. I extend here the concept of reflex epilepsy to epilepsies linked to input dependent physiological systems. Experimental and clinical reseach data were collected to create a coherent explanation of underlying pathomechanism in AE and NFLE. We propose that AE should be interpreted as epilepsy linked to the corticothalamic burst-firing mode of NREM sleep, released by evoked vigilance level oscillations characterized by reactive slow wave response. In the genetic variation of NFLE the ascending cholinergic arousal system plays an essential role being in strong relationship with a gain mutation of the nicotinic acethylcholin receptors, rendering the arousal system hyperexcitable. I try to provide a more unitary interpretation for the variable seizure manifestation integrating them as different degree of pathological arosuals and alarm reactions. As a supporting hypothesis the similarity between arousal parasomnias and FNLE is shown, underpinned by overlaping pathomechanism and shared familiarity, but without epileptic features. Lastly we propose that both AE and NFLE are system epilepsies of the sleep-wake system representing epileptic disorders of the antagonistic sleep/arousal network. This interpretation may throw new light on the pathomechanism of AE and NFLE.

Pre- and post-dormitum epilepsies: idiopathic generalized epilepsies

Epilepsy and sleep have a profound bidirectional influence. Idiopathic generalized epilepsy (IGE) comprises a fascinating group of syndromes that constitute nearly one-third of all epilepsies. These syndromes are genetically determined and affect otherwise normal people of both sexes and all races. IGE manifests with typical absences, myoclonic jerks, and generalized tonic-clonic seizures, alone or in varying combinations and severity. IGE syndromes are typically modulated by the sleep-wake cycle, and particularly by the sleep-wake transition process, both in terms of the occurrence of seizures and interictal epileptiform discharges (IED), with pronounced susceptibility to sleep deprivation. IGE analysis from the point of view of arousal modulation enhances the concept of a biological continuum existing among IGE syndromes. At the same time, this analysis broaches the problem of syndromic diagnosis and identification of the factors influencing the phenotypic expression of some epileptic phenomena over the course of life with potential bidirectional influences between epileptic manifestations and sleep-wake processes.

Bimodal ultradian seizure periodicity in human mesial temporal lobe epilepsy

BACKGROUND

Mesial temporal lobe epilepsy (mTLE) has been suggested to follow a circadian rhythm. Previous research found an afternoon peak in mTLE seizure occurrence. We evaluated the pattern of seizure occurrence in patients with well-localized mTLE and hypothesized that peak seizure frequency would occur in the afternoon, and that this pattern would not be altered by age, gender, or seizure focus.

METHODS

We retrospectively identified consecutive mTLE patients with a seizure-free outcome following anterior temporal lobectomy from 1993 to 2004 with video-EEG captured seizures. We recorded and plotted the 24-h clock time for each seizure and performed cosinor analysis. SAS Proc GLIMMIX was used to fit the linearized transform of the cosinor model. Negative binomial regression fitted by the generalized estimating equations (GEE) method was also performed to estimate and compare the mean seizure rates over a 24-h day.

RESULTS

Sixty mTLE patients monitored between 2 and 16 days were analyzed. Mean (standard deviation), median number of seizures per subject were 10.47(7.86), 9.00. Cosinor plots indicated that the function had two modes: 7-8 a.m. and 4-5 p.m. GEE analysis was consistent with peak seizure frequency occurrence at 6-8 a.m. (p<0.0001) and 3-5 p.m. (p<0.01).

CONCLUSIONS

We found a bimodal pattern of seizure occurrence in human mTLE, with peak seizure frequencies occurring between 6-8 a.m. and 3-5 p.m. confirming an afternoon peak, as well as a previously unsuspected morning peak in seizure occurrence that provides rationale for future investigations of antiepileptic drug chronopharmacology and informs patient counseling regarding patterns of seizure occurrence.

Sleep and epilepsy: what we know, don't know, and need to know

Long-term video-EEG and, more recently, video-polysomnography, have provided the means to confirm and expand on the interconnections between sleep and epilepsy. Some of these relationships have become firmly established. When one of the authors (N.F.S.) presented part of this paper at a symposium on the Future of Sleep in Neurology at an American Clinical Neurophysiology Society annual meeting in 2004, the purpose was to summarize what we know, don't know, and need to know about the effects of sleep on epilepsy and epilepsy on sleep. Here we seek to summarize some of the more firmly established relationships between sleep and epilepsy and identify intriguing associations that require further elucidation.

Seizure clustering

Seizure clusters, also known as repetitive or serial seizures, occur commonly in epilepsy. Clustering implies that the occurrence of one seizure may influence the probability of a subsequent seizure; thus, the investigation of the clustering phenomenon yields insights into both specific mechanisms of seizure clustering and more general concepts of seizure occurrence. Seizure clustering has been defined clinically as a number of seizures per unit time and, statistically, as a deviation from a random distribution, or interseizure interval dependence. This review explores the pathophysiology, epidemiology, and clinical implications of clustering, as well as other periodic patterns of seizure occurrence. Risk factors for experiencing clusters and potential precipitants of clustering are also addressed.

Effect of sleep deprivation on spike-wave discharges in idiopathic generalised epilepsy: a 4 x 24 h continuous long term EEG monitoring study

The aim of the study was to investigate the effect of sleep and sleep deprivation on spike-wave discharges (SWD) in an idiopathic generalised epileptic patient population by continuous long term cassette EEG monitoring for 4 x 24 h. In ten patients with idiopathic generalised epilepsy, showing SWD during awake state and in sleep as well, EEG and sleep polygraphy was recorded for 4 x 24 h. Sleep was deprived during the second 24 h. Awake state, NREM1, NREM2, NREM3+4 and REM sleep duration and number of SWD episodes were evaluated in 4 min intervals by visual scoring. For analysing the effect of 'day' and 'night', 'vigilance' and 'sleep deprivation' (SD) on the density variables multi-way ANOVAs were carried out in different designs. SWD densities for different vigilance states were not significantly different during 'day' and 'night' in 24 h without SD or rebound after SD. Sleep had an activating effect SWD densities being the highest during NREM1 and NREM2. There was an increase of SWD densities in all vigilance states after SD, but SWD densities remained the highest in NREM1 andNREM2. Our results support the view that sleep dependent rather than sleep independent mechanisms cause activation of SWD after SD in generalised epilepsy. We assume that fine graded vigilance fluctuations, that are more frequent after SD, have an essential role in SWD activation in superficial sleep or even in wakefulness.

Spike-wave discharge and the microstructure of sleep-wake continuum in idiopathic generalised epilepsy

This review summarises all the evidences about the influence of different vigilance states on the occurrence of spike wave discharge (SWD) in idiopathic generalised epilepsy (IGE) patients. Numerous converging observations showed that full REM-sleep and alert wakefulness exert strong inhibition. A critical zone of vigilance which is a transitional state between waking and non-REM (NREM) sleep, and NREM sleep and REM sleep, has a promoting effect on the absence type spike wave discharge. Spike wave discharges are associated with phasic arousals without awakening and are attached to oscillation son the microstructural level of sleep, perpetuated by cyclic arousal events known as 'cyclic alternating pattern' (CAP), especially within the critical zone, but also along the whole sleep process. More specifically SWD seems to be attached to the 'A-phase' of CAP which is a reactive one and reflects synchronised NREM sleep EEG elements, like K-complexes, spindles and delta groups. The more slow wave elements are found in phase A--like in subtype A1--the more the coincidence with SWD occurs, and the more it is characterised by fast rhythms--as in subtype A2 and A3--the less the association with SWD could be observed. Since subtype A1 is associated with the first sleep cycle and with the descending branches of cycles, it is concluded that SWD appear in those dynamic moments of vigilance level oscillations which were characterised by strong sleep-like answers to arousal influences in high sleep pressure periods of sleep cyclicity. These data harmonize with another line of evidence suggesting that SWD represent the epileptic variant of the complex thalamocortical system function which is the substrate of NREM sleep EEG phenomena. In idiopathic generalised epilepsy there is a growing body of evidence that--as it was assumed by Gloor--spindles transform to SWD pattern. These data explain why those dynamic changes which evoke sleep responses are promoting for the occurrence of SWD. Adapting these data we offer a new interpretation to explain the strong activation effect of sleep deprivation in this kind of epilepsy. We assume that it is mainly due to the forced vigilance level oscillations, especially in morning, when elevated sleep pressure and circadian wake promoting forces, representing opposite tendencies, increase the amount of oscillations.

Sleep-EEG modulation of interictal epileptiform discharges in adult partial epilepsy: a spectral analysis study

INTRODUCTION

In order to define accurately the relationship between EEG components (spindles, delta and theta frequencies) and the occurrence of interictal epileptiform discharges (IED) during sleep in partial epilepsy, a correlation study between spike overnight distribution and EEG spectral power time series was performed.

METHODS

Eighteen patients (mean age: 24.7+/-5.5 years) affected by partial epilepsy underwent continuous EEG-polysomnography. The temporal series of Slow Wave Activity (SWA), Sigma Activity (SA) and Theta Band (TB), derived from spectral analysis, were obtained from a spike-free and pathologic alteration-free derivation, contralateral to the most active lead, where the IED count was performed. Relationships between SA, SWA and TB and time series of IED were tested by means of correlation techniques after data normalization.

RESULTS

Our results revealed a significantly higher correlation between IED and SWA in 12 subjects; a significantly higher correlation between IED and SA in three subjects and a significant correlation with TB in three cases.

CONCLUSIONS

Data suggest that in most adult patients with partial epilepsy IED production during sleep is facilitated by the action of synchronizing mechanisms which are active during NREM sleep and lead to the appearance of EEG delta waves. Nevertheless evidence is given of two smaller groups of patients. In one of them IED are more sensitive to the promoting action of the spindle generating mechanism, active during stage 2 of NREM sleep. In the other one the promoting action of TB, characterizing EEG during stage 1 and REM sleep, is evident.

Effects of circadian regulation and rest-activity state on spontaneous seizures in a rat model of limbic epilepsy

PURPOSE

Circadian regulation via the suprachiasmatic nuclei and rest-activity state may influence expression of limbic seizures.

METHODS

Male rats (n = 14) were made epileptic by electrical stimulation of the hippocampus, causing limbic status epilepticus and subsequent seizures. We monitored seizures with intrahippocampal electrodes in 12-12-h light/dark (LD) cycles and in continuous dark (DD). We used radiotelemetry monitoring of activity to measure state and body temperature to determine circadian phase. Cosinor analysis and chi2 tests determined whether seizures occurred rhythmically when plotted by phase. State was defined as inactive or active in 10-min epochs based on whether activity count was below or above a cut-off value validated from video observation.

RESULTS

In LD, the peak seizure occurrence was 14:59 h after circadian temperature peak (95% confidence limit, 13:37-16:19). Phasic seizure occurrence persisted in DD for 14:05 (12:31-15:38), p < 0.0001, against uniform mean distribution. In LD, 14,787 epochs contained 1, 268 seizures; seizures preferentially occurred during inactive epochs (965 observed, 878 expected in proportion to the overall distribution of inactive versus active epochs; p < 0.001). In DD, 20, 664 epochs contained 1,609 seizures; seizures had no preferential occurrence by state (999 observed, 1,025 expected; p = 0.16).

CONCLUSIONS

Limbic seizures occurred with an endogenous circadian rhythm. Seizures preferentially struck during inactivity during entrainment to the light-dark cycle.

Sleep apnea treatment improves seizure control in children with neurodevelopmental disorders

Seizure disorder and sleep apnea are common chronic disorders in children, but the relationship between sleep apnea and seizure control has not been studied in the pediatric population. This retrospective review included nine children with neurodevelopmental disorders who had well-documented sleep apneic episodes and seizure disorders. Seizure frequency was reduced in five patients (56%) in the first 12 months after sleep apnea treatment without changes in their antiepileptic medications. Sleep apnea can be one of the seizure precipitants in children with epilepsy. This study indicates the importance of identifying sleep apnea when treating children with intractable epilepsy, particularly in those who are at high risk.

Effects of sleep and sleep stage on epileptic and nonepileptic seizures

PURPOSE

Previous studies of patients with epilepsy and animal models of epilepsy suggest that sleep increases the frequency, duration, and secondary generalization of seizures. This information is, however, incomplete.

METHODS

We retrospectively examined video-EEG monitoring reports from our comprehensive epilepsy center. We recorded seizure type, site of onset (for partial seizures), sleep state at onset, and whether partial seizures secondarily generalized. Seizures arising from sleep were then reviewed to determine sleep state.

RESULTS

We analyzed 1,116 seizures in 188 patients. Thirty-five percent of complex partial seizures (CPSs) starting during sleep underwent secondary generalization compared with 18% in wakefulness (p < 0.0001). Frontal lobe CPSs secondarily generalized at equal rates during sleep (22%) and wakefulness (20%), but temporal lobe CPSs generalized much more frequently during sleep (45%) than in wakefulness (19%; p < 0.0001). Frontal lobe seizures were more likely to occur during sleep (37%) than were temporal lobe seizures (26%; p = 0.0068). CPSs were more frequent in stages 1 and 2 and occurred rarely during REM. Seizures starting during slow-wave sleep were significantly longer than seizures starting during wakefulness or stage 2 sleep. Psychogenic nonepileptic seizures (PNESs) were rare between midnight and 6 a m. and never occurred during sleep.

CONCLUSIONS

Sleep has a pronounced effect on secondary generalization of partial seizures, especially those of temporal lobe origin. Frontal lobe seizures occur more often during sleep than do temporal lobe seizures, and occurrence during sleep helps to distinguish PNESs from CPSs.

Effect of seizures and epileptiform discharges on cognitive function

Several relationships have been obtained between cognitive impairment and epilepsy-related or treatment-related factors. One of these factors is treatment-related: the central cognitive side effects of the antiepileptic drugs (AEDs). The second and third factors are disease-related factors, i.e., the effect of the seizures and underlying epileptiform discharges in the brain and the localization of the epileptogenic focus in specific areas of the brain. Although most cognitive problems have a multifactorial origin and often several factors combined are responsible for the "make-up" of a cognitive problem, we have attempted to isolate one factor: the effect of seizures and epileptiform EEG discharges on cognitive function. Several studies show the impact of ictal activity, but special attention is required for the postictal and interictal effects of epilepsy on cognitive functions. This may explain substantial cognitive impairments in children with subclinical epileptiform discharges or with infrequent subtle seizures.

Circadian rhythm, sleep, and epilepsy

This review article: (1) describes the circadian distribution of ictal and interictal events; (2) differentiates transitional arousal, non-rapid eye movement and rapid eye movement sleep components and their substrates; (3) suggests the means by which the neural generators of these seizure-prone vs. seizure-resistant sleep and arousal states modulate the timing of different seizure manifestations; (4) considers clinical and mechanistic findings for the reciprocal effects of seizures and antiepileptic drugs upon the sleep-wake cycle; and (5) assesses clinical and basic mechanisms of sleep deprivation effects upon seizures.

Seizure frequency in intractable partial epilepsy: a statistical analysis

We examined the seizure records of 13 patients (nine men and four women, ages 27-50 years) with intractable partial epilepsy, maintained with steady anti-epileptic drug dosages. Patients recorded daily seizure frequency on calendars. Periods of outpatient observation ranged from 99 to 1,710 days and the number of observed seizures ranged from 18 to over 400, with daily seizure rates of 0.1-4.3 per day. We used the quasi-likelihood regression model to examine the following four departures of the daily seizure counts from a Poisson (random) model: (1) linear increasing or decreasing time trends in expected seizure rates; (2) clustering, where the expected seizure rate on a given day depends on the number of seizures observed on the immediate prior days; (3) monthly cyclicity; and (4) increased variability (overdispersion). Linear time trends were seen in six patients (four increasing and two decreasing), clustering was seen in 10 patients, and a near-monthly cycle appeared in four patients (two of nine men and two of four women). A significant amount of extra variation (overdispersion) relative to a Poisson distribution was observed in all but one of the 13 patients. Departures from a Poisson (random) model appear more common in this population of patients with medically intractable epilepsy than is commonly recognized, and have clinical importance as well as implications for the design of clinical studies.

Spike-wave discharges and sleep-wake states in rats with absence epilepsy

The occurrence of spike-wave discharges was studied in relation to the daily fluctuations of vigilance level in rats. Eight rats of the WAG/Rij strain, an animal model for idiopathic generalized epilepsy of the absence type, which were equipped with cortical EEG and nuchal EMG electrodes, served as subjects. It was found that spike-wave discharges predominantly occur during light slow wave sleep and passive wakefulness. REM sleep, active wakefulness, and deep slow wave sleep are less susceptible to the occurrence of spike-wave discharges. Finally, spike-wave discharges tend to prevail in transitional states. A crucial role for the degree of stability of the level of vigilance in the genesis of absence seizures is suggested.

Absence epilepsy and the level of vigilance in rats of the WAG/Rij strain

In man, a relationship exists between sleep-wake states and absence epilepsy. During wakefulness, spike-wave discharges predominantly occur when the level of vigilance is not high, while during sleep they have a preference to occur during slow-wave sleep. During this latter type of sleep, spike-wave discharges prevail in periods where slow-wave sleep is light. In a series of experiments, the WAG/Rij rat model for absence epilepsy was characterized with respect to the relationships between the level of vigilance, sleep-wake states and the occurrence of spike-wave discharges. In the first experiment, continuous recordings were made for a period of 48 h and a clear circadian rhythm was established for the number of spike-wave discharges. A maximum appeared during the middle of the dark period of the rat, whereas a minimum was detected directly after the onset of the light period, the time period during which deep slow-wave sleep predominates. The relationship of spike-wave discharges with states of vigilance was elaborated in a second study. Spike-wave discharges were mainly found during light slow-wave sleep, during passive wakefulness and in transition phases from sleep to wakefulness. During REM sleep no spike-wave discharges were found. In the last three experiments, the level of alertness was enhanced by various procedures as photostimulation, a learning task and deprivation of REM sleep. In all cases, an increase of alertness decreased the amount of epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of the interictal epileptiform EEG activity during sleep: from oscillations to complex dynamics

Polygraphic sleep recordings (EEG, EMG, and EOG) were performed in two groups of epileptic subjects, six with fragile-X syndrome and six with symptomatic epilepsy. Recordings were visually scored for sleep stages and number of spikes/min. Subjects with fragile-X syndrome showed a well defined pattern of production of interictal epileptiform activity with the lowest values during REM sleep; symptomatic epileptic subjects showed less defined and more variable spike/min diagrams. The spectral analysis of the outline of such diagrams confirmed these differences showing shorter periodicities (80-100 min) in the fragile-X group compared to those of the symptomatic group (160-220 min). Finally, a model with multiple feedback circuits is proposed in order to explain the different patterns observed.

Wakefulness-sleep modulation of EEG-EMG epileptiform activities: a quantitative study on a child with intractable epilepsia partialis continua

Continuous all night recordings of epileptiform EEG activities from right frontal scalp and thalamic Centromedian regions and EMG activities from left deltoid muscular region were performed on a child with intractable epilepsia partialis continua, with depth stimulating-recording electrodes used for neuroaugmentive seizure control. In addition, "normal" and "mature" sleep indicators in the same child were simultaneously recorded according to the International Procedures. During wakefulness (W), type B seizures consisted of isolated, high amplitude, negative-positive EEG sharp waves recorded from the right Centromedian region (RCM sharp) correlated with isolated bursts of high amplitude EMG potentials recorded from the left deltoid muscle (LEMG jerks). Type C seizures consisted of clusters of repetitive RCM sharp and LEMG jerks, where individual EEG-EMG activities showed poor correlations. Number and amplitude of type B RCM sharp and LEMG jerks significantly decreased when patient directly shifted from W to slow wave sleep I and II (SWSI and II). Number and amplitude of RCM sharp increased while those of LEMG jerks decreased directly from SWS I and II to slow wave sleep III (SWS III); all forms of EEG-EMG epileptiform type B activities significantly decreased directly or indirectly from W and SWS to paradoxical sleep (PS). Scalp EEG spikes from right frontal and central regions showed almost parallel changes to those of RCM sharp, except during SWS II, when amplitude increased in the former and decreased in the later. Occurrence of type C seizures only decreased during PS and duration decreased directly from SWS I to II and indirectly from SWS I to SWS II and PS; and from W to SWS II and III and PS.

Preliminary evaluation of potential anti-epileptic drugs by single dose electrophysiological and pharmacological studies in patients

In phase 1 evaluation of potential anti-epileptic drugs (AEDs), insufficient attention has perhaps been directed to the transition from single, and multi-dose studies in normal volunteers to clinical trials of some weeks duration in patients. Acute single dose studies in epileptic patients already receiving AEDs may reduce avoidable errors in early controlled trials. Acute single dose studies provide the opportunity of obtaining some preliminary evidence of efficacy by observing the effects of the drug on quantified epileptiform EEG discharges, both those occurring spontaneously in long term telemetric recordings and those elicited by standardised photic stimulation in susceptible subjects. The pharmacokinetics of the new drug may be profoundly influenced by the comedication (as illustrated by lamotrigine, the half life of which varies by a factor of 10 depending on comedication). Conversely, the new drug may so influence metabolism of the comedication that the results of add-on trials may be virtually uninterpretable, unless steps are taken to maintain blood levels of the other AEDs. A method of addressing this problem is illustrated in the case of an imidazole, R57720. Adverse experiences may also occur more readily when a new drug is added to comedication than when it is given to normal volunteers and these problems in chronic trials can be anticipated from acute studies.

Circadian rhythmicity in absence epilepsy in rats

In order to study putative time of day effects upon the number and mean duration of spike-wave complexes, 19 rats of the WAG/Rij strain were equipped with cortical EEG electrodes. The EEGs were recorded continuously for 48 h. A cosinor analysis was applied to both the data on each subject and the mean scores of all rats. A definite 24 h rhythm was found for the number of spike-wave complexes occurring each hour. The acrophase appeared during the early hours of the dark period, while the minimum was found to take place immediately after the onset of light. A 24 h rhythm was less prominent for the mean duration of the spike-wave complexes. Finally, there were no differences found between the 2 days of the 48 h registration period, suggesting that the number and duration of the spike-wave complexes found on a given day are representative for the following day.

Sleep studies in benign epilepsy of childhood with rolandic spikes. II. Analysis of discharge frequency and its relation to sleep dynamics

Polygraphic all-night sleep recordings of 11 children with benign epilepsy of childhood with rolandic spikes (BERS) were investigated from the viewpoint of spike distribution. Spike/min ratios were calculated with regard to different sleep stages and waking, identical stages of the consecutive cycles, and stages 1-2 taking place on the descending versus the ascending slopes of sleep cycles. Maximum spike/min ratios were related to slow sleep stages, especially delta sleep, and in general to the first cycle. Stages 1-2 on the descending (DESC) slopes of consecutive cycles showed a decrease in spike density during the night, as opposed to the increasing rate of activation of the same stages on the ascending (ASC) slopes. Based on our results, we suggest that the actual drive of spiking as well as seizures in BERS is the functional overweight of sleep-inducing mechanisms.

Electroencephalographic findings in antiepileptic drug trials: a review and report of 6 studies

A recent survey has shown that the EEG is of doubtful value as an outcome variable in clinical antiepileptic drug (AED) trials. Analysis of findings in 6 trials shows that in only two no consistent effect was seen; that in two power spectral analysis provided additional information to confirm changes in background activity; that in one a close relationship could be established between reduction in frequency of epileptiform discharges and administration of the trial drug (lamotrigine), and that in one, even though no correlation was apparent during use of the AED, there was an increase in frequency of both discharges and seizures on withdrawal (CGP 11952). In general the EEG would appear to be unsuitable as an outcome variable for assessing drug efficacy in AED trials. On the other hand it may give insight into the mode of drug action. Conceivably more efficient use could be made of the EEG if the methodology--including patient selection, consideration of circadian rhythms and of combination AED therapy, and standardized long-term recording--were to be improved and automation and quantification techniques used.

State disorders and state-dependent seizures in amygdala-kindled cats

This study replicated and extended previous work indicating a reciprocal relationship between persistent sleep disorders and seizure susceptibility in amygdala-kindled cats. Eight kindled cats (experimental group) and six nonkindled cats (control group) were assessed for several sleep and waking state parameters. Seizure susceptibility, indexed by thresholds to generalized afterdischarge and tonic-clonic convulsions, was also evaluated in experimental subjects during each of the following states: alert but quiet wakefulness, slow-wave sleep, transitions from slow-wave to REM sleep, and REM sleep. There were two primary findings: (i) slow-wave sleep and transitions from it to REM sleep were disrupted in amygdala-kindled cats whereas REM sleep was normal when an effective transition had been made; and (ii) disturbed states were also more susceptible to generalized seizures than were stable REM sleep and waking episodes, suggesting that abnormal rather than normal sleep created a predisposition for seizures.

Epileptic seizure disorders. Developments in diagnosis and therapy

There has been considerable progress in various segments of epileptology over the past two to three decades. The diagnostic sector has benefited from more advanced and sophisticated EEG-related techniques. The advent of computerized tomography has expedited the clinical evaluation of epileptic patients and new high-technology methods have been introduced. A new type of diagnostic subdivision (based on age-determined epileptic conditions and certain epileptic syndromes) is of great practical significance because of its prognostic implications (distinction of basically benign and severe forms of epileptic seizure disorders). The therapeutic sector has been stimulated by the introduction of new antiepileptic medications and particularly by profound insights into metabolic and pharmacokinetic characteristics of anticonvulsants; this has resulted in the introduction of techniques for serum level determinations. There have been new developments in the field of neurosurgical treatment of epileptic seizure disorders.

Temporal characteristics of seizures and epileptiform discharges

The time relations of epileptic events have been studied in 3 sets of data: (I) counts of individual epileptiform discharges in twelve 48 h EEG recordings, (IIa) seizure calendars of 30 therapy-resistant outpatients participating in a drug trial, (IIb) seizure calendars of 10 mentally subnormal epileptic patients resident in a long-stay unit. The EEG data I were characterized most often by a Poisson distribution of intervals between discharges and the occurrence of marked periodicities, particularly at night. The periods of rhythmic nocturnal events ranged from 13 to 142 min and did not appear to correspond to the REM/non-REM cycle. In the seizure data IIa and b a Poisson distribution of intervals between events was found in half the patients. Periodicities occurred only in group IIa and did not correspond to weekly or monthly cycles. A stochastic process is considered to be the model which best fits these data.

The circadian distribution of interictal epileptiform EEG activity

Eighteen continuous 48 h monitoring studies are reported from 17 patients with epilepsy. The numbers of epileptiform discharges over corresponding epochs of the 2 days were significantly positively correlated in 16 studies. However, this was explicable by masking due to the sleep/wake cycle and when waking and sleep were considered separately a minority of studies showed significant correlations. The difference in total 24 h production of discharges between the 2 days ranged from 1.3 to 30.3%, mean 15.1%. The maximum discharge rate in 75% of the studies occurred during sleep; during waking the distribution of discharges was random. Even in the waking state the 0.5 h discharge rate was extremely variable and in few patients could a single 30 min epoch be regarded as a reliable sample of the mean rate over the waking day. The intervals between events showed a Poisson distribution during 9 days and 5 nights, but there was no within-patient consistency between the first and second 24 h period. The occurrence of discharges was periodic significantly more often at night than during the day, but the periodicities did not clearly correspond to the REM cycle. Discharges increased overall during sleep in 14 studies, were unchanged in 2 and decreased in 4. The time of occurrence of maximal discharge rate during sleep was consistent from night I to night II only in patients exhibiting generalized regular spike-wave activity but random in the others. A negative correlation between antiepileptic drug levels and discharge rate was rarely observed.

Machine detection of spike-wave activity in the EEG and its accuracy compared with visual interpretation

Machine detection of epileptiform activity in the EEG is useful in seizure monitoring because of its inherent consistency and the rapid data reduction it can provide. Devices based on a few detection criteria have lacked reliability of detection and those with more complex algorithms have sacrificed operating speed and portability. This paper describes a largely analog device which detects irregular as well as classic spike and wave activity. It is portable and it can process the accelerated playback of 24 h tape recorders as well as real-time EEG. It recognizes spikes by their shape and waves by their frequency. It makes inter-channel comparisons to identify trains of bilateral synchronous spikes, generalized waves, and coincidence of spikes and waves and furnishes a limited description of each event in terms of these characteristics. The device was tested against the judgment of 3 experienced and certified electroencephalographers in 18 h of EEG containing 769 bursts of spike-wave activity from 6 patients. It detected 96.5% of the consensus spike and wave activity (i.e., activity identified by all 3 electroencephalographers). Only 0.56% of the machine's detections were false positives (i.e., activity identified by none of the electroencephalographers), though the false positive rate was higher in the presence of chewing artifact. It measured burst duration with an average error of 0.43 sec/burst. While reader-machine agreement varied somewhat by patient, in general, the machine disagreed with the consensus no more than the readers disagreed with each other. In a second reading session after 6 months, the amount of activity identified by the readers changed by an amount ranging from 2.4% to 57% while the machine was consistent within a few tenths of 1%. Hence, this paper demonstrates that by implementing a multi-criteria detection algorithm in special purpose circuitry, a cost-effective solution to the problem of reliable machine detection of spike and wave activity can be obtained.

Epilepsy in adults

The past decade has seen advances in the management of patients with epilepsy. The development of practical long-term electroencephalographic techniques, with or without simultaneous video recording, has increased the accuracy of diagnosis of seizure types. The technique also provides clinicians and investigators with a method for establishing the clinical efficacy of antiepileptic drugs and determining their therapeutic serum concentrations. Computerized tomography has enhanced the identification of structural brain lesions. Most of the reported CT abnormalities consist of diffuse and focal atrophies, mild ventricular dilatations, and porencephalies. CT has detected tumors in 8 to 10% of the patients regardless of age or type of seizure involved. New concepts of antiepileptic drug therapy have developed from the recognition of pharmacological properties peculiar to each agent. Determination of serum antiepileptic drug levels has to be utilized to reduce the problem of pharmacokinetic variability from one patient to another and in the same patient at different times, so that dosage can be individualized to achieve maximum therapeutic effects with least toxicity. Review of the literature on pregnancy in epileptic women shows that a third to half experienced more seizures during gestation. Reduced serum levels of most antiepileptic drugs have recently been observed during gestation. Infants of epileptic women taking antiepileptic drugs have a two to three times greater risk for congenital anomalies than infants of nonepileptic women. However, with the exception of oxazolidinediones, evidence to date has not proved the teratogenicity of antiepileptic drugs. The role of genetic factors and the effect of seizures during pregnancy have not been determined. Modest progress has been made in epilepsy rehabilitation, but serious problems still remain. The unemployment rate of persons with epilepsy is twice the national average. Half of those who are successfully employed did not disclose their disorder at the time of employment. Several prognostic indicators have been reported, but the validity of many of these indicators is questionable. For example, does shorter life expectancy apply to all subgroups, or does it vary according to seizure type and cause? The life expectancy, treatment response, and probability of remission in epileptic persons must be reevaluated after consistent applications of current methods of epilepsy management.

[Temporal organization of paroxysmal discharges in the child. II. Polygraphic recordings during sleep]

A study of the paroxysmal activities in the course of all night sleep was carried out on 6 children aged 6 to 12 years, who were previously recored by means of biotelemtry during the day (cf. Findji et al. 1978). The discharges were analysed and quantified in the same way as in daytime but here in relation to the organization of sleep. The latter shows serious disturbances by comparison with normal children or children who only have sleep problems. The global quantifications (average densities of discharges per stage) do not, in our population, evidence any effect of facilitation or diminution which would be specific to a given stage. Comparison of the chronological evolutions of the densities of paroxysmal activities with the different stages of sleep shows that the connections between these phenomena can be either nil, or very close, according to the subject, and in one case, according to the time of night. This raises the problem of the heterogeneity of the 'states' gathered under the same codification of stages and shows the multiplicity of factors which can interfere with the modulation of the discharges, even during sleep. The analysis of long duration day or night records underlines the extreme complexity of the temporal organization of paroxysmal discharges, in which both hypotheses formulated at the beginning of this study seem to find partial support: internal modulation connected to more or less stable biological rhythms, and the role of environmental factors and the subject's reactions, which more or less mask the intrinsic rhythms.

[Temporal organization of paroxysmal discharges in the child. I. Biotelemetric recordings during wakefulness]

Based on telemetric recordings performed on 6 children, a study of the time distribution of intra-clinical paroxysmal discharges was carried out. It was tested whether this distribution is stochastic, and if not so, whether is depends upon an internal biological rhythm or upon environmental and behavioural factors. The times of occurrence of paroxysmal discharges, generalized and/or focal or partial, were located by visual inspection, and fed into a computer for statistical evaluation. Discharges and intervals were thus quantified for the overall recording time, for one situation or for groups of situations; the chronological distribution of discharges during successive 300 sec epochs was also computed. In all the cases, the discharge density varied from one moment to the next, but not in random fashion: the hypothesis of an internal modulation of the discharges was verified in some specific cases, more often, the changes in the discharge chronology seemed to be related to modifications of psychophysiological states observed during the successive experimental situations. The factors involved, namely, alertness, specific attention, stress, posture, etc., seemed to play a different role in each case; no simple correlation with the topography of discharges could be established. One explanation does not exclude the other: modulation of the discharges by biological rhythms could at any time be masked by variations due to environmental factors and to the subject's specific reaction to the latter. This type of study presents considerable methodological and interpretative difficulties which tend to emphasize individual differences rather than allowing to draw general laws.

Seizure moitoring: a new tool in electroencephalography

A seizure monitoring system, based on telemetry and computer techniques, has been developed to provide a reliable means of recording the patient's spontaneous seizures. It allows a patient's EEG to be monitored for hours or days with 16 channels of EEG from surface, sphenoidal or stereotaxically implanted depth electrodes, from any ward or room within the hospital. The EGG is delayed in time by up to 4 min by a mini-computer so that either the patient can push a button when he experiences his aura or others can push the button when they observe his seizure. Since the delayed EEG is written out, the preictal, ictal and postictal are recorded on paper, without many pages of uneventful interictal information. During the past 16 months, the seizure monitoring system has been used as a clinical service to examine patients with surface electrodes (42), sphenoidal wires (25) and depth electrodes (7) during 146 recording sessions for over 3200 h of monitoring time while over 200 seizures have been recorded.