Awareness and responsiveness during partial seizures

Pure amnestic seizure: A clinico-intracranial EEG study

OBJECTIVE

Enduring anterograde amnesia is caused by lesions in bilateral mesial temporal lobes. However, whether transient dysfunction of bilateral mesial temporal regions induces reversible amnesia has not been proven. We investigated this association in patients with epilepsy and analyzed the electroclinical correlation during pure amnestic seizures (PAS). PAS are defined as seizures with anterograde amnesia as the only ictal manifestation, accompanied by preserved responsiveness and other cognitive functions.

METHODS

We retrospectively searched our intracranial EEG database to find PAS. Pure ictal amnesia was confirmed by immediate and comprehensive ictal examinations.

RESULTS

Among 401 patients who underwent intracranial EEG recording, three patients with temporal lobe epilepsy (TLE) manifesting PAS were identified. The patients talked and behaved normally during seizure but did not remember the episodes afterwards. Ictal discharges were confined to bilateral mesial temporal regions, with no or mild involvement of surrounding structures. Spread of low-voltage fast activities to bilateral mesial temporal regions corresponded to onset of ictal anterograde amnesia. Two patients underwent unilateral mesial temporal resection and became seizure-free with improvement in cognitive functions.

SIGNIFICANCE

PAS is a rare ictal semiology in TLE. Bilateral mesial temporal regions that play a critical role in memory encoding are presumably the symptomatogenic zones for PAS.

Female sex steroids and epilepsy: Part 2. A practical and human focus on catamenial epilepsy

Catamenial epilepsy is the best described and most researched sex steroid-specific seizure exacerbation. Yet despite this there are no current evidence-based treatments, nor an accepted diagnostic tool. The best tool we currently have is tracking seizures over menstrual cycles; however, the reality of tracking seizures and menstrual cycles is fraught with challenges. In Part 1 of this two-part review, we outlined the often complex and reciprocal relationship between seizures and sex steroids. An adaptable means of tracking is required. In this review, we outline the extent and limitations of current knowledge on catamenial epilepsy. We use sample data to show how seizure exacerbations can be tracked in short/long and even irregular menstrual cycles. We describe how seizure severity, an often overlooked and underresearched form of catamenial seizure exacerbation, can also be tracked. Finally, given the lack of treatment options for females profoundly affected by catamenial epilepsy, Section 3 focuses on current methods and models for researching sex steroids and seizures as well as limitations and future directions. To permit more informative, mechanism-focused research in humans, the need for both a consistent classification of catamenial epilepsy and an objective biomarker is highlighted.

Clinical utility of a video/audio-based epilepsy monitoring system Nelli

OBJECTIVE

The aim of this study was to evaluate the clinical utility of a semi-automated hybrid video/audio-based epilepsy monitoring system (Nelli®) in a home setting.

METHODS

In this retrospective study, 104 consecutive patients underwent Nelli-registration for an average of 29 days at their home. The seizure-related data obtained from the registration were assessed to investigate the utility of the Nelli-registration regarding clinical decision-making.

RESULTS

Of 104 patients, Nelli® hybrid system was able to recognize clinically relevant events in 83 (80%) patients: epileptic seizures in 67 (65%) and nonepileptic events in 16 (15%). A total of 2767 epileptic seizures of different seizure types were captured and identified. These seizures included not only tonic-clonic seizures but also other complex or simple motor seizures. For the outcomes regarding clinical decision-making, a need for a new therapeutic intervention was recognized in 54 (51.9%) patients based on the number and severity of seizures captured by Nelli-registration. In 12 (11.5%) patients, the need to change the treatment plan was excluded because no evidence of suspected epileptic seizures was found. Nelli-registration aided in confirming the therapeutic efficacy of modifications of antiseizure medications (ASMs) or neuromodulation therapies in 13 (12.5%) patients. Nelli-registration enabled to determine the change in seizure classification and facilitated to reach clear diagnostic conclusions in 11 (10.6%) patients. In 14 (13.5%) patients, there was no change in clinical outcome, as Nelli-registration was unable to infer any clinical decision either due to inconclusive results or lack of typical events. Seizures detected during Nelli-registration aided in decision-making for therapeutic interventions in 71 (68%) patients. Altogether, 44 (42%) patients had adjustment of ASMs, and in 9 (9%) patients, Nelli-registrations led to the change in the settings of vagus nerve stimulation (VNS) or deep brain stimulation (DBS) treatment. Additionally, 18 (17%) patients were referred to presurgical evaluation or established a baseline seizure frequency before surgical implantation for neuromodulation treatment with VNS or DBS, while 33 (32%) patients had no change in therapy. Nine patients (8.7%) were referred to video-EEG monitoring (VEM), as Nelli-recorded events highlighted the need for presurgical evaluation in 6 patients or further diagnostic evaluation in 3 patients.

CONCLUSION

This study confirms the clinical utility of the video/audio monitoring system Nelli® in home settings. Home monitoring with Nelli® hybrid system provides a new alternative for the assessment of frequency and type of epileptic seizures as well as for a recognition of nonepileptic events. Thus, Nelli-registration can facilitate the optimization of seizure monitoring and management in clinical practice, complementing existing methods such as VEM and ambulatory EEG recordings.

Seizure semiology: ILAE glossary of terms and their significance

This educational topical review and Task Force report aims to address learning objectives of the International League Against Epilepsy (ILAE) curriculum. We sought to extract detailed features involving semiology from video recordings and interpret semiological signs and symptoms that reflect the likely localization for focal seizures in patients with epilepsy. This glossary was developed by a working group of the ILAE Commission on Diagnostic Methods incorporating the EEG Task Force. This paper identifies commonly used terms to describe seizure semiology, provides definitions, signs and symptoms, and summarizes their clinical value in localizing and lateralizing focal seizures based on consensus in the published literature. Video-EEG examples are included to illustrate important features of semiology in patients with epilepsy.

Reliability of patient self-report of cognition, awareness, and consciousness during seizures

Objective

Clinicians rely on patient self‐report of impairment during seizures for decisions including driving eligibility. However, the reliability of patient reports on cognitive and behavioral functions during seizures remains unknown.

Methods

We administered a daily questionnaire to epilepsy patients undergoing continuous video‐EEG monitoring, asking about responsiveness, speech, memory, awareness, and consciousness during seizures in the preceding 24 hours. We also administered a questionnaire upon admission about responsiveness, speech, and awareness during seizures. Subjective questionnaire answers were compared with objective behavioral ratings on video review. Criteria for agreement were Cohen’s kappa >0.60 and proportions of positive and negative agreement both >0.75.

Results

We analyzed 86 epileptic seizures in 39 patients. Memory report on the daily questionnaire met criteria for agreement with video review (κ = 0.674 for early, 0.743 for late recall). Subjective report of awareness also met agreement criteria with video ratings of memory (κ = 0.673 early, 0.774 late). Concordance for speech was relatively good (κ = 0.679) but did not meet agreement criteria, nor did responsiveness or consciousness. On the admission questionnaire, agreement criteria were met for subjective report of awareness versus video ratings of memory (κ = 0.814 early, 0.806 late), but not for other comparisons.

Interpretation

Patient self‐report of memory or awareness showed the best concordance with objective memory impairment during seizures. Self‐report of impairment in other categories was less reliable. These findings suggest that patient reports about impaired memory during seizures may be most reliable, and otherwise determining functional impairments should be based on objective observations.

Semi-supervised automatic seizure detection using personalized anomaly detecting variational autoencoder with behind-the-ear EEG

BACKGROUND AND OBJECTIVE

Epilepsy is one of the most common neurologic diseases worldwide, and 30% of the patients live with uncontrolled seizures. For the safety of patients with epilepsy, an automatic seizure detection algorithm for continuous seizure monitoring in daily life is important to reduce risks related to seizures, including sudden unexpected death. Previous researchers applied machine learning to detect seizures with EEG, but the epileptic EEG waveform contains subtle changes that are difficult to identify. Furthermore, the imbalance problem due to the small proportion of ictal events caused poor prediction performance in supervised learning approaches. This study aimed to present a personalized deep learning-based anomaly detection algorithm for seizure monitoring with behind-the-ear electroencephalogram (EEG) signals.

METHODS

We collected behind-the-ear EEG signals from 16 patients with epilepsy in the hospital and used them to develop and evaluate seizure detection algorithms. We modified the variational autoencoder network to learn the latent representation of normal EEG signals and performed seizure detection by measuring the anomalies in EEG signals using the trained network. To personalize the algorithm, we also proposed a method to calibrate the anomaly score for each patient by comparing the representations in the latent space.

RESULTS

Our proposed algorithm showed a sensitivity of 90.4% with a false alarm rate of 0.83 per hour without personal calibration. On the other hand, the one-class support vector machine only showed a sensitivity of 84.6% with a false alarm rate of 2.17 per hour. Furthermore, our proposed model with personal calibration achieved 94.2% sensitivity with a false alarm rate of 0.29 while detecting 49 of 52 ictal events.

CONCLUSIONS

We proposed a novel seizure detection algorithm with behind-the-ear EEG signals via semi-supervised learning of an anomaly detecting variational autoencoder and personalization method of anomaly scoring by comparing latent representations. Our approach achieved improved seizure detection with high sensitivity and a lower false alarm rate.

Seizure documentation in people living with epilepsy

Seizure documentation is an essential component of epilepsy management. Not all persons with epilepsy choose to document their seizures, but many view the practice as essential to managing their disease. While seizure documentation is a valuable aspect of patient care, clinicians and patients must remain aware that seizure underreport and overreport commonly occur due to lack of seizure awareness. Additionally, in rare cases, persons with epilepsy may intentionally conceal their seizures from clinicians. The continued development of electronic seizure diaries and epilepsy self-management software provides patients with new and expanding options for seizure documentation and disease management. In order for these tools to be utilized most effectively, patient input must be central to their development. Given the limitations of seizure documentation, the development of accurate, non-invasive seizure detection devices is crucial for accurate seizure monitoring.

Unsupervised automatic seizure detection for focal-onset seizures recorded with behind-the-ear EEG using an anomaly-detecting generative adversarial network

BACKGROUND AND OBJECTIVE

Epilepsy is a neurological disorder of the brain, which involves recurrent seizures. An encephalogram (EEG) is a gold standard method in the detection and analysis of epileptic seizures. However, the standard EEG recording system is too obstructive to be used in daily life. Behind-the-ear EEG is an alternative approach to record EEG conveniently. Previous researchers applied machine learning to automatically detect seizures with EEG, but the epileptic EEG waveform contains subtle changes that are difficult to be identified. Furthermore, the extremely small proportion of ictal events in the long-term monitoring may cause the imbalance problem and, consequently, poor prediction performance in supervised learning approaches. In this study, we present an automatic seizure detection algorithm with a generative adversarial network (GAN) trained by unsupervised learning and evaluated it with behind-the-ear EEG.

METHODS

We recorded behind-the-ear EEGs from 12 patients who have various types of epilepsy. Data were reviewed separately by two epileptologists, who determined the onsets and ends of seizures. First, we conducted unsupervised learning with the normal records for the GAN to learn the representation of normal states. Second, we performed automatic seizure detection with the trained GAN as an anomaly detector. Last, we combined the Gram matrix with other anomaly losses to improve detection performance.

RESULTS

The proposed approach achieved detection performance with an area under the receiver operating curve of 0.939 and sensitivity of 96.3% with a false alarm rate of 0.14 per hour in the test dataset. In addition, we confirmed distinguishability with the distribution of the anomaly scores in terms of EEG frequency bands.

CONCLUSIONS

It is expected that the proposed anomaly detection via GAN with the behind-the-ear EEG can be effectively used for long-term seizure monitoring in daily life.

Which seizure elements do patients memorize? A comparison of history and seizure documentation

OBJECTIVE

People with epilepsy (PWE) are frequently unable to recall the core manifestation of their disease, epileptic seizures. This means that seizure frequency is often underestimated by practitioners and that seizure classification based on reports of patients or their relatives is difficult because seizure semiology remains unclear. The purpose of this study, therefore, was to prospectively explore patients' memory regarding seizure elements and to assess the role of seizure types.

METHOD

Ninety patients diagnosed with focal epilepsy undergoing diagnostic electroencephalography (EEG)-video monitoring were included. The ability to memorize individual seizure elements was assessed using a questionnaire. Patient knowledge was then compared to the findings of subsequent seizure documentation during EEG-video monitoring. Seizure elements were categorized in four groups: subjective, motor, autonomic, and postictal elements.

RESULTS

In all categories, the number of documented seizure elements during monitoring strongly exceeded the number of elements that were recalled. Only 45.6% of subjective elements, 5.4% of motor phenomena, 11.9% of autonomic findings, and 2.1% of postictal impairments were recalled. The ability to recall seizure elements varied significantly depending on seizure types (secondarily generalized tonic-clonic seizures [SGTCS] < complex partial seizures [CPS] < simple partial seizures [SPS]), but not on the relative timing of the element during the seizure.

SIGNIFICANCE

Patients' memory of seizure semiology is almost always fragmentary. Although the rate of correctly remembered seizure elements depends on the seizure type, complete recall of a seizure is almost never obtained. Consequently, 89 of 90 patients in this cohort would only have had seizures classified as a seizure with "impaired awareness" according to the new International League Against Epilepsy (ILAE) seizure classification. The involvement of brain areas involved in memory encoding and consolidation and in the context of seizure classification schemes.

Structured testing during seizures: A practical guide for assessing and interpreting ictal and postictal signs during video EEG long term monitoring

BACKGROUND

Ictal and postictal testing carried out in long-term epilepsy monitoring units is often sub-optimal. Recently, a European consensus protocol for testing patients during and after seizures was developed by a joint taskforce of the International League Against Epilepsy - Commission on European Affairs and the European Epilepsy Monitoring Unit Association.

AIM

Using this recently developed standardised assessment battery as a framework, the goal of this narrative review is to outline the proposed testing procedure in detail and explain the rationale for each individual component, focusing on the underlying neurobiology. This is intended to serve as an educational resource for staff working in epilepsy monitoring units.

METHODS

A literature review of PubMed was performed; using the search terms "seizure", "ictal", "postictal", "testing", "examination", and "interview". Relevant literature was reviewed and relevant references were chosen. The work is presented as a narrative review.

RESULTS

The proposed standardised assessment battery provides a comprehensive and user-friendly format for ictal-postictal testing, and examines consciousness, language, motor, sensory, and visual function.

CONCLUSION

The standardised approach proposed has the potential to make full use of data recorded during video EEG increasing the diagnostic yield with regards to lateralisation and localisation, aiding both presurgical and diagnostic studies.

Viewing their own seizures improves understanding of disease in people with epilepsy

BACKGROUND

People with epilepsy (PWE) are frequently unable to recall the core manifestation of their disease, epileptic seizures. This limits their understanding of disease severity and social reactions to it.

PURPOSE

The purpose of this study was to assess the effects of video presentation (VP) of one's own seizure and the role of seizure type/severity.

METHODS

Ninety patients diagnosed with focal epilepsy undergoing diagnostic video-electroencephalography (EEG) monitoring were included. All participants were presented with a seizure of their predominant seizure type on videotape. Effects of viewing seizures were assessed using a questionnaire immediately after the VP (T1), after 3 days (T2), and after 3 months (T3).

RESULTS

Of the participants, 97.6%, 87.2%, and 85.2% considered VP as helpful at T1, T2, and T3, respectively. Participants who viewed a more severe seizure tended to assess the VP as more helpful, related to an improved understanding of the disease and of reaction of others to their seizures. Of the participants, 11.5% and 5.0% perceived the VP as stressful at T2 and T3, respectively. Severity of the presented seizure was positively correlated to the level of stress induced, mostly because of a feeling of helplessness based on ictal loss of control.

CONCLUSIONS

The VP of the patients' own seizures is a way to improve the patients' knowledge on their disease, which was appreciated by the vast majority of participants. The VP of severe seizures was regarded more informative yet also more stressful. Further research is needed to examine possible effects on quality of life and compliance.

Subjective seizure counts by epilepsy clinical drug trial participants are not reliable

PURPOSE

Self-reported seizure counts of patients with epilepsy guide individual treatment decisions and often represent the primary outcome measure of pharmacological trial in epileptology. The validity of these data has recently been challenged and the question is whether this applies to participants of clinical studies as well. Here we compared self-estimated seizure counting and documentation accuracy in participants and nonparticipants of former epilepsy clinical drug trials.

METHODS

Adult participants (N=100) from a total of twenty-two phase II, III or IV clinical drug studies performed at our unit (2002-2015) underwent a structured telephone interview on self-estimated seizure awareness and seizure documentation accuracy. Data were compared to data from a recent study in adult epilepsy patients (N=132) who never participated in clinical trials and who answered the same questions (Blachut et al., Seizure 2015; 29:97-103).

RESULTS

Reported seizure frequencies, self-estimated seizure documentation accuracy (at best 46-53%), and the motivation for seizure-documentation were almost identical in both groups and no group effect was found except for higher self-reported awareness for nocturnal seizures in former study participants.

CONCLUSION

Epilepsy patients having participated in clinical drug trials report comparable erroneous seizure counts as do epilepsy patients in general. These data further corroborate the notion that most clinical trials in epileptology are based on inaccurate measures. Implications and possible solutions for patients, physicians, and research are discussed.

Seizing upon mechanisms for impaired consciousness

Transient loss of consciousness associated with focal temporal lobe seizures is a complex phenomenon with life-threatening repercussions. In this issue of Neuron, Motelow et al. (2015) describe decreased cholinergic drive and suppressed subcortical arousal in seizures as a novel mechanism for impaired cortical function.

Epilepsy and driving: potential impact of transient impaired consciousness

Driving is an important part of everyday life for most adults, and restrictions on driving can place a significant burden on individuals diagnosed with epilepsy. Although sensorimotor deficits during seizures may impair driving, decreased level of consciousness often has a more global effect on patients' ability to respond appropriately to the environment. Better understanding of the mechanisms underlying alteration of consciousness in epilepsy is important for decision-making by people with epilepsy, their physicians, and regulators in regard to the question of fitness to drive. Retrospective cohort and cross-sectional studies based on surveys or crash records can provide valuable information about driving in epilepsy. However, prospective objective testing of ictal driving ability during different types of seizures is needed to more fully understand the role of impaired consciousness and other deficits in disrupting driving. Driving simulators adapted for use in the epilepsy video-EEG monitoring unit may be well suited to provide both ictal and interictal data in patients with epilepsy. Objective information about impaired driving in specific types of epilepsy and seizures can provide better informed recommendations regarding fitness to drive, potentially improving the quality of life of people living with epilepsy.

Alteration of consciousness in focal epilepsy: the global workspace alteration theory

Alteration of consciousness (AOC) is an important clinical manifestation of partial seizures that greatly impacts the quality of life of patients with epilepsy. Several theories have been proposed in the last fifty years. An emerging concept in neurology is the global workspace (GW) theory that postulates that access to consciousness (from several sensorial modalities) requires transient coordinated activity from associative cortices, in particular the prefrontal cortex and the posterior parietal associative cortex. Several lines of evidence support the view that partial seizures alter consciousness through disturbance of the GW. In particular, a nonlinear relation has been shown between excess of synchronization in the GW regions and the degree of AOC. Changes in thalamocortical synchrony occurring during the spreading of the ictal activity seem particularly involved in the mechanism of altered consciousness. This link between abnormal synchrony and AOC offers new perspectives in the treatment of the AOC since means of decreasing consciousness alteration in seizures could improve patients' quality of life.

Consciousness of seizures and consciousness during seizures: are they related?

Recent advances have been made in the network mechanisms underlying impairment of consciousness during seizures. However, less is known about patient awareness of their own seizures. Studying patient reports or documentation of their seizures is currently the most commonly utilized mechanism to scientifically measure patient awareness of seizures. The purpose of this review is to summarize the available evidence regarding the accuracy of patient seizure counts and identify the variables that may influence unreliable seizure reporting. Several groups looking at patient documentation of seizures during continuous EEG monitoring show that patients do not report as many as 50% of their seizures. These studies also suggest that seizures accompanied by loss of consciousness, arising from the left hemisphere or the temporal lobe, or occurring during sleep are associated with significantly reduced reporting. Baseline memory performance does not appear to have a major influence on the accuracy of seizure report. Further prospective studies using validated ictal behavioral testing as well as using correlation with newer electrophysiological and neuroimaging techniques for seizure localization are needed to more fully understand the mechanisms of underreporting of seizures. Better methods to alert caregivers about unrecognized seizures and to improve seizure documentation are under investigation.

Global disorders of consciousness

In recent decades there has been a great deal of interest in global disorders of consciousness, such as the vegetative state, the minimally conscious state, and epileptic absence seizures. Global disorders of consciousness pose significant challenges to consciousness science in that the ordinary pretheoretical criteria for the ascription of consciousness are not easily applied in such contexts, and it is often unclear what kinds of conscious states-if any-patients are in. At the same time, global disorders of consciousness also promise to reveal a great deal about the nature of consciousness and the relationship between consciousness and cognitive and behavioral control. WIREs Cogn Sci 2014, 5:129-138. doi: 10.1002/wcs.1270 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Prospective assessment of ictal behavior using the revised Responsiveness in Epilepsy Scale (RES-II)

Impaired consciousness in epilepsy has a significant negative impact on patients' quality of life yet is difficult to study objectively. Here, we develop an improved prospective Responsiveness in Epilepsy Scale-II (RES-II) and report initial results compared with the earlier version of the scale (RES). The RES-II is simpler to administer and includes both verbal and non-verbal test items. We evaluated 75 seizures (24 patients) with RES and 34 seizures (11 patients) with RES-II based on video-EEG review. The error rate per seizure by test administrators improved markedly from a mean of 2.01 ± 0.04 with RES to 0.24 ± 0.11 with RES-II. Performance during focal seizures showed a bimodal distribution, corresponding to the traditional complex partial vs. simple partial seizure classification. We conclude that RES-II has improved accuracy and testing efficiency compared with the original RES. Prospective objective testing will ultimately lead to a better understanding of the mechanisms of impaired consciousness in epilepsy.

The assessment of consciousness during partial seizures

A wide range of controversial definitions and dynamic components surround the multi-dimensional concept of consciousness, with important reflections on the phenomenological description of ictal states relevant to epileptic seizures. The inadequacies of terminology, the insufficient emphasis on the subjective nature of consciousness, as well as the intrinsic limitations of the simple versus complex dichotomy for partial seizures, are to be considered in view of a modern definition of consciousness. In this paper, we review the difficulties encountered by clinicians in assessing the ictal conscious state in patients with epilepsy, and illustrate how a more sophisticated bi-dimensional model of consciousness can prove a valuable conceptual tool for the clinical assessment of ictal consciousness and the categorization of seizures.

Impaired consciousness in epilepsy investigated by a prospective responsiveness in epilepsy scale (RES)

PURPOSE

Impaired consciousness in epileptic seizures has a major negative impact on patient quality of life. Prior work on epileptic unconsciousness has mainly used retrospective and nonstandardized methods. Our goal was to validate and to obtain initial data using a standardized prospective testing battery.

METHODS

The responsiveness in epilepsy scale (RES) was used on 52 patients during continuous video-electroencephalography (EEG) monitoring. RES begins with higher-level questions and commands, and switches adaptively to more basic sensorimotor responses depending on patient performance. RES continues after seizures and includes postictal memory testing. Scoring was conducted based on video review.

KEY FINDINGS

Testing on standardized seizure simulations yielded good intrarater and interrater reliability. We captured 59 seizures from 18 patients (35% of participants) during 1,420 h of RES monitoring. RES impairment was greatest during and after tonic-clonic seizures, less in partial seizures, and minimal in auras and subclinical seizures. In partial seizures, ictal RES impairment was significantly greater if EEG changes were present. Maximum RES impairment (lowest ictal score) was also significantly correlated with long postictal recovery time, and poor postictal memory.

SIGNIFICANCE

We found that prospective testing of responsiveness during seizures is feasible and reliable. RES impairment was related to EEG changes during seizures, as well as to postictal memory deficits and recovery time. With a larger patient sample it is hoped that this approach can identify brain networks underlying specific components of impaired consciousness in seizures. This may allow the development of improved treatments targeted at preventing dysfunction in these networks.

Impaired consciousness in temporal lobe seizures: role of cortical slow activity

Impaired consciousness requires altered cortical function. This can occur either directly from disorders that impair widespread bilateral regions of the cortex or indirectly through effects on subcortical arousal systems. It has therefore long been puzzling why focal temporal lobe seizures so often impair consciousness. Early work suggested that altered consciousness may occur with bilateral or dominant temporal lobe seizure involvement. However, other bilateral temporal lobe disorders do not impair consciousness. More recent work supports a 'network inhibition hypothesis' in which temporal lobe seizures disrupt brainstem-diencephalic arousal systems, leading indirectly to depressed cortical function and impaired consciousness. Indeed, prior studies show subcortical involvement in temporal lobe seizures and bilateral frontoparietal slow wave activity on intracranial electroencephalography. However, the relationships between frontoparietal slow waves and impaired consciousness and between cortical slowing and fast seizure activity have not been directly investigated. We analysed intracranial electroencephalography recordings during 63 partial seizures in 26 patients with surgically confirmed mesial temporal lobe epilepsy. Behavioural responsiveness was determined based on blinded review of video during seizures and classified as impaired (complex-partial seizures) or unimpaired (simple-partial seizures). We observed significantly increased delta-range 1-2 Hz slow wave activity in the bilateral frontal and parietal neocortices during complex-partial compared with simple-partial seizures. In addition, we confirmed prior work suggesting that propagation of unilateral mesial temporal fast seizure activity to the bilateral temporal lobes was significantly greater in complex-partial than in simple-partial seizures. Interestingly, we found that the signal power of frontoparietal slow wave activity was significantly correlated with the temporal lobe fast seizure activity in each hemisphere. Finally, we observed that complex-partial seizures were somewhat more common with onset in the language-dominant temporal lobe. These findings provide direct evidence for cortical dysfunction in the form of bilateral frontoparietal slow waves associated with impaired consciousness in temporal lobe seizures. We hypothesize that bilateral temporal lobe seizures may exert a powerful inhibitory effect on subcortical arousal systems. Further investigations will be needed to fully determine the role of cortical-subcortical networks in ictal neocortical dysfunction and may reveal treatments to prevent this important negative consequence of temporal lobe epilepsy.

Definition of the postictal state: when does it start and end?

The postictal state is the abnormal condition occurring between the end of an epileptic seizure and return to baseline condition. Applying this definition operationally can be difficult, especially for complex partial seizures, where cognitive and sensorimotor impairments merge imperceptibly into the postictal state. Many patients are unaware of even having had a seizure. Electroencephalography sometimes helps to distinguish ictal from postictal periods, but may demonstrate focal slowing both during and after a seizure. Epileptiform electroencephalographic changes do not always correspond precisely to behavioral changes, especially with scalp recordings. The postictal state ends at the interictal state, but this too can be ambiguous. Interictal spikes and spike-waves can be associated with cognitive and behavioral impairments, suggesting that they may represent fragments of ictal episodes. Except where boundaries are clear, it is better to describe a sequence of behaviors and electroencephalographic changes, without labeling arbitrary stages as being ictal or postictal.

Memory for public events in patients with unilateral temporal lobe epilepsy

Memory for public events (PEs) was assessed as a marker of remote declarative memory in 36 patients with temporal lobe epilepsy (TLE) and compared with that of 19 patients with extra-TLE (ETLE), 17 patients with idiopathic generalized epilepsy (IGE), and 23 healthy volunteers. Verbal IQ, inventory-based evidence of depression, handedness, onset of illness, disease duration, and medication were obtained. Memory for PEs was reduced in all patient groups (TLE, P<0.0001; ETLE, P=0.009; IGE, P=0.008). The TLE group showed reduced memory for PEs compared with the other patients with epilepsy (P=0.001). A time gradient was observed, with worse memory for PEs of the 1990 s and for PEs that occurred after onset of illness. Our data support the key role of the temporal lobe in remote declarative memory. With patients with TLE remembering fewer PEs from the period after onset of epilepsy, the deficits can be partly attributed to unsuccessful consolidation rather than retrieval difficulties alone.

The real truth behind seizure count

Epilepsy: Accuracy of Patient Seizure Counts. Hoppe C, Poepel A, Elger CE. Arch Neurol 2007;64(11):1595–1599. OBJECTIVE: To evaluate the effects of a daily patient reminder on seizure documentation accuracy. DESIGN: Randomized controlled trial. SETTING: Monitoring unit of an academic department of epileptology. PATIENTS: Consecutive sample of 91 adult inpatients with focal epilepsies undergoing video-electroencephalographic monitoring. INTERVENTION: While all patients were asked to document seizures at the beginning of the monitoring period, patients from the experimental group were reminded each day to document seizures. MAIN OUTCOME MEASURE: Documentation accuracy (percentage of documented seizures). RESULTS: A total of 582 partial seizures were recorded. Patients failed to document 55.5% of all recorded seizures, 73.2% of complex partial seizures, 26.2% of simple partial seizures, 41.7% of secondarily generalized tonic-clonic seizures, 85.8% of all seizures during sleeping, and 32.0% of all seizures during the awake state. The group medians of individual documentation accuracies for overall seizures, simple partial seizures, complex partial seizures, and secondarily generalized tonic-clonic seizures were 33.3%, 66.7%, 0%, and 83.3%, respectively. Neither the patient reminder nor cognitive performance affected documentation accuracy. A left-sided electroencephalographic focus or lesion, but not the site (frontal or temporal), contributed to documentation failure. CONCLUSIONS: Patient seizure counts do not provide valid information. Documentation failures result from postictal seizure unawareness, which cannot be avoided by reminders. Unchanged documentation accuracy is a prerequisite for the use of patient seizure counts in clinical trials and has to be demonstrated in a subsample of patients undergoing electroencephalographic monitoring.

Theories of impaired consciousness in epilepsy

Although the precise mechanisms for control of consciousness are not fully understood, emerging data show that conscious information processing depends on the activation of certain networks in the brain and that the impairment of consciousness is related to abnormal activity in these systems. Epilepsy can lead to transient impairment of consciousness, providing a window into the mechanisms necessary for normal consciousness. Thus, despite differences in behavioral manifestations, cause, and electrophysiology, generalized tonic-clonic, absence, and partial seizures engage similar anatomical structures and pathways. We review prior concepts of impaired consciousness in epilepsy, focusing especially on temporal lobe complex partial seizures, which are a common and debilitating form of epileptic unconsciousness. We discuss a "network inhibition hypothesis" in which focal temporal lobe seizure activity disrupts normal cortical-subcortical interactions, leading to depressed neocortical function and impaired consciousness. This review of the major prior theories of impaired consciousness in epilepsy allows us to put more recent data into context and to reach a better understanding of the mechanisms important for normal consciousness.

Consciousness and epilepsy: why are complex-partial seizures complex?

Why do complex-partial seizures in temporal lobe epilepsy (TLE) cause a loss of consciousness? Abnormal function of the medial temporal lobe is expected to cause memory loss, but it is unclear why profoundly impaired consciousness is so common in temporal lobe seizures. Recent exciting advances in behavioral, electrophysiological, and neuroimaging techniques spanning both human patients and animal models may allow new insights into this old question. While behavioral automatisms are often associated with diminished consciousness during temporal lobe seizures, impaired consciousness without ictal motor activity has also been described. Some have argued that electrographic lateralization of seizure activity to the left temporal lobe is most likely to cause impaired consciousness, but the evidence remains equivocal. Other data correlates ictal consciousness in TLE with bilateral temporal lobe involvement of seizure spiking. Nevertheless, it remains unclear why bilateral temporal seizures should impair responsiveness. Recent evidence has shown that impaired consciousness during temporal lobe seizures is correlated with large-amplitude slow EEG activity and neuroimaging signal decreases in the frontal and parietal association cortices. This abnormal decreased function in the neocortex contrasts with fast polyspike activity and elevated cerebral blood flow in limbic and other subcortical structures ictally. Our laboratory has thus proposed the "network inhibition hypothesis," in which seizure activity propagates to subcortical regions necessary for cortical activation, allowing the cortex to descend into an inhibited state of unconsciousness during complex-partial temporal lobe seizures. Supporting this hypothesis, recent rat studies during partial limbic seizures have shown that behavioral arrest is associated with frontal cortical slow waves, decreased neuronal firing, and hypometabolism. Animal studies further demonstrate that cortical deactivation and behavioral changes depend on seizure spread to subcortical structures including the lateral septum. Understanding the contributions of network inhibition to impaired consciousness in TLE is an important goal, as recurrent limbic seizures often result in cortical dysfunction during and between epileptic events that adversely affects patients' quality of life.

Do recent seizures and recent changes in antiepileptic drugs impact performances on neuropsychological tests in subtle ways that might easily be missed?

PURPOSE

The possibility that a recent seizure or a recent change in antiepileptic medication might produce an occult change in neuropsychological performance is of interest, and especially so in the context of evaluation for epilepsy surgery. Such an evaluation is often done in a setting of video-EEG monitoring where a strong effort is made to produce seizures as quickly as possible with abrupt changes in medication, alterations in sleep, etc., which could impact the validity of neuropsychological findings.

METHODS

A total of 126 adults were studied who had seizures of strictly temporal origin (47 right, 79 left) and whose recent medication history and seizure occurrence prior to testing was as clear as possible. All were tested with an extensive neuropsychological battery with great attention to giving tests only when the patients appeared clinically not to be suffering from recent seizures (seizures occurring on the day of testing or on the day prior to testing) or medication change effects. The cognitive correlates of side of seizures were also evaluated in order to provide a strength-of-effect comparison with recency of AED changes and seizures.

RESULTS

Findings from three-way ANOVA showed a possible slight adverse effect of recent AED change, no effects of recent seizures, and a sizeable relationship with side of seizures. A simultaneous consideration of all three of these variables did not provide additional findings of interest.

CONCLUSIONS

Although it is not possible to completely rule out some subtle cognitive effects of recent changes in medication or recent seizures, this investigation does not provide evidence for such effects when the neuropsychological evaluation is conducted carefully with no testing during any questionable or definite postictal periods.

When do patients forget their seizures? An electroclinical study

Accurate knowledge of the frequency of epileptic seizures is a precondition for evaluating the efficacy of pharmacotherapy. It is a well-known fact that the information provided by epilepsy patients about the number of seizures they experience is often unreliable. In the present study, we aimed to identify predictors of a higher risk of unrecognized events. Thirty patients who underwent presurgical evaluation in a video/EEG monitoring unit were recruited. As soon as the patient became aware of a seizure, he or she completed a standardized questionnaire on the subjective perception of the seizure, which was then compared with the video/EEG findings. Of the 138 seizures recorded, 49.3% were reliably detected by the patient, whereas 44.2% went unnoticed; the remainder were incompletely or uncertainly perceived. Subjects in whom events occurred during sleep or originated in (or propagated to) the left temporal lobe had a significantly higher percentage of unrecognized events.

Consciousness, epilepsy, and emotional qualia

The last decade has seen a renaissance of consciousness studies, witnessed by the growing number of scientific investigations on this topic. The concept of consciousness is central in epileptology, despite the methodological difficulties concerning its application to the multifaced ictal phenomenology. The authors provide an up-to-date review of the neurological literature on the relationship between epilepsy and consciousness and propose a bidimensional model (level vs contents of consciousness) for the description of seizure-induced alterations of conscious states, according to the findings of recent neuroimaging studies. The neurophysiological correlates of ictal loss and impairment of consciousness are also reviewed. Special attention is paid to the subjective experiential states associated with medial temporal lobe epilepsy. Such ictal phenomenal experiences are suggested as a paradigm for a neuroscientific approach to the apparently elusive philosophical concept of qualia. Epilepsy is confirmed to represent a privileged window over basic neurobiological mechanisms of consciousness.

Effects of epileptiform EEG discharges on cognitive function: is the concept of "transient cognitive impairment" still valid?

In this article we review the existing evidence on the cognitive impact of interictal epileptiform EEG discharges. Such cognitive impairment occurs exclusively in direct relation to episodes of epileptiform EEG discharges and must be distinguished from (post) ictal seizure effects and from the nonperiodic long-term "stable" interictal effects caused by the clinical syndrome or the underlying etiology. Especially in patients with short nonconvulsive seizures, characterized often by difficult-to-detect symptoms, the ictal or postictal effects may be overlooked and the resulting cognitive effects may be erroneously related to the epileptiform EEG discharges. The existing epidemiological data show that the prevalence of cognitive impairment during epileptiform EEG discharges is low. In one study 2.2% of the patients referred to a specialized epilepsy center for EEG recording showed a definite relationship between epileptiform EEG discharges and cognitive impairments ("transient cognitive impairment"). Several studies have sought to analyze to what extent cognitive impairment can be attributed to epileptiform EEG discharges among the other epilepsy factors (such as the effect of the clinical syndrome). These studies show that epileptiform EEG discharges have an additional and independent effect, but this effect is mild and limited to transient mechanistic cognitive processes (alertness, mental speed). This finding concurs with clinical studies that also reported only mild effects. In only exceptional cases are epileptiform EEG discharges the dominant factor explaining cognitive impairment. In addition, some studies have indicated that such mild effects may accumulate over time (when frequent epileptiform EEG discharges persist over years) and consequently result in effects on stable aspects of cognitive function such as educational achievement and intelligence. Hence, the clinical relevance is that early detection of cognitive effects of epileptiform EEG discharges and subsequent treatment may prevent a definite impact on cognitive and educational development. The disruptive effects of epileptiform EEG discharges on long-term potentiation, as established in animal experiments, may be one of the neurophysiological mechanisms underlying this accumulation. In conclusion the concept of "transient cognitive impairment" is still valid, but refinement of methodology has shown that a large proportion of presumed transient cognitive impairment can be attributed to subtle seizures, while interictal epileptic activity accounts for a much smaller part of the cognitive effects than previously thought. In particular cryptogenic partial epilepsies are associated with the risk of cognitive impairment. We hope that increased clinical awareness of this need for early detection will stimulate longitudinal and prospective research that eventually also will provide an answer to the questions of when and how epileptiform discharges that are not part of a seizure need to be treated.

Why do seizures cause loss of consciousness?

Model systems are needed for the scientific investigation of consciousness. A good model system should include variable states of consciousness, allowing the relationship between brain activity and consciousness to be investigated. Examples include sleep, anesthesia, focal brain lesions, development, evolution, and epilepsy. One advantage of epilepsy is that changes are dynamic and rapidly reversible. The authors review previous investigations of impaired consciousness in epilepsy and describe new findings that may shed light on both normal and abnormal mechanisms of consciousness. Abnormal increased activity in fronto-parietal association cortex and related subcortical structures is associated with loss of consciousness in generalized seizures. Abnormal decreased activity in these same networks may cause loss of consciousness in complex partial seizures. Thus, abnormally increased or decreased activity in the same networks can cause loss of consciousness. Information flow during normal conscious processing may require a dynamic balance between these two extremes of excitation and inhibition.

Level and contents of consciousness in connection with partial epileptic seizures

The present study introduces concepts and methods that can be used in the systematic psychological study of a seizure, to gain more insight into the seizure as it is experienced by the patient and the significant other. Fourteen patients reported 40 descriptions of their subjective experiences during complex partial seizures. We analyzed the descriptions with respect to the temporal progression of the seizure and the level and contents of consciousness. There were three main findings: (1). We identified an impairment of the voluntary control of attention ("forced attention") that seems to characterize the early stages of the seizure in all patients. (2). Although most patients reported the total absence of consciousness, we identified a subgroup of patients with a fluctuating level of consciousness during the seizure. (3). The patients who reported some contents of consciousness during the seizure were found to usually experience internal mental images rather than other contents of consciousness (e.g., sensations or perceptions). We propose that use of a qualitative methodology for the psychological assessment of seizures could lead to a better understanding of seizures as experienced from the patient's perspective and thereby to improvements in the treatment of seizures.

Involvement of the thalamocortical system in epileptic loss of consciousness

Experiments on putative neuronal mechanisms underlying absence seizures as well as clinical observations are critically reviewed for their ability to explain apparent "loss of consciousness." It is argued that the initial defect in absences lies with corticothalamic (CT) neuronal mechanisms responsible for selective attention and/or planning for action, rather than with those establishing either the states or the contents of consciousness. Normally, rich thalamocortical (TC)-CT feedback loops regulate the flow of information to the cortex and help its neurons to organize themselves in discrete assemblies, which through high-frequency (>30 Hz) oscillations bind those distributed processes of the brain that are considered important, so that we are able to focus on what is needed from moment to moment and be aware of this fact. This ability is transiently lost in absence seizures, because large numbers of CT loops are recruited for seconds in much stronger, low-frequency ( approximately 3 Hz) oscillations of EPSP/IPSP sequences, which underlie electroencephalographic (EEG) spike-and-wave discharges (SWDs). These oscillations probably result from a transformation of the normal EEG rhythm of sleep spindles on an abnormal increase of cortical excitability that results in strong activation of inhibitory neurons in the cortex and in nucleus reticularis thalami. The strong general enhancement of CT feedback during SWDs may disallow the discrete feedback, which normally selects specific TC circuits for conscious perception and/or motor reaction. Such a mechanism of SWD generation allows variability in the extent to which different TC sectors are engaged in the SWD activity and thus explains the variable ability of some patients to respond during an absence, depending on the sensory modality examined.

Nonconvulsive status epilepticus in rats: impaired responsiveness to exteroceptive stimuli

An animal model of human complex partial status epilepticus induced by lithium chloride and pilocarpine administration was developed in our laboratory. The objective of the study was to provide a detailed analysis of both ictal and postictal behavior and to quantify seizure-related morphological damage. In order to determine the animal's responsiveness to either visual or olfactory stimuli, adult male rats were submitted to the following behavioral paradigms: the object response test, the social interaction test, and the elevated plus-maze test. The rotorod test was used to evaluate motor performance. Two weeks after status epilepticus, brains were morphologically examined and quantification of the brain damage was performed. Profound impairment of behavior as well as responsiveness to exteroceptive stimuli correlated with the occurrence of epileptic EEG activity. When the epileptic EEG activity ceased, responsiveness of the pilocarpine-treated animals was renewed. However, remarkable morphological damage persisted in the cortical regions two weeks later. This experimental study provides support for the clinical evidence that even nonconvulsive epileptic activity may cause brain damage. We suggest that the model can be used for the study of both functional and morphological consequences of prolonged nonconvulsive seizures.

Alterations in NMDA receptors in a rat model of cortical dysplasia

Recent studies have demonstrated an important role for the N-methyl-D-aspartate receptor (NMDAR) in epilepsy. NMDARs have also been shown to play a critical role in hyperexcitability associated with several animal models of human epilepsy. Using whole-cell voltage clamp recordings in brain slices, we studied evoked paroxysmal discharges in the freeze-lesion model of neocortical microgyria. The voltage dependence of epileptiform discharges indicated that these paroxysmal events were produced by a complex pattern of excitatory and inhibitory inputs. We examined the effect of the NMDAR antagonist D-2-amino-5-phosphopentanoic acid (APV) and the NMDA receptor subunit type 2B (NR2B)-selective antagonist ifenprodil on the threshold, peak amplitude, and area of evoked epileptiform discharges in brain slices from lesioned animals. Both compounds consistently raised the threshold for evoking the discharge but had modest effects on the discharge peak and amplitude. For comparison with nonlesioned cortex, we examined the effects of ifenprodil on the epileptiform discharge evoked in the presence of 2 microM bicuculline (partial disinhibition). In slices from nonlesioned cortex, 10 microM ifenprodil had little effect on the threshold whereas 71% of the recordings in bicuculline-treated lesioned cortex showed a >25% increase in threshold. These results suggest that NR2B-containing receptors are functionally enhanced in freeze-lesioned cortex and may contribute to the abnormal hyperexcitability observed in this model of neocortical microgyria.