Impaired consciousness in epilepsy

Restoring Conscious Arousal During Focal Limbic Seizures with Deep Brain Stimulation

Impaired consciousness occurs suddenly and unpredictably in people with epilepsy, markedly worsening quality of life and increasing risk of mortality. Focal seizures with impaired consciousness are the most common form of epilepsy and are refractory to all current medical and surgical therapies in about one-sixth of cases. Restoring consciousness during and following seizures would be potentially transformative for these individuals. Here, we investigate deep brain stimulation to improve level of conscious arousal in a rat model of focal limbic seizures. We found that dual-site stimulation of the central lateral nucleus of the intralaminar thalamus (CL) and the pontine nucleus oralis (PnO) bilaterally during focal limbic seizures restored normal-appearing cortical electrophysiology and markedly improved behavioral arousal. In contrast, single-site bilateral stimulation of CL or PnO alone was insufficient to achieve the same result. These findings support the "network inhibition hypothesis" that focal limbic seizures impair consciousness through widespread inhibition of subcortical arousal. Driving subcortical arousal function would be a novel therapeutic approach to some forms of refractory epilepsy and may be compatible with devices already in use for responsive neurostimulation. Multisite deep brain stimulation of subcortical arousal structures may benefit not only patients with epilepsy but also those with other disorders of consciousness.

Multi-modal analysis of functional connectivity and cerebral blood flow reveals shared and unique effects of propofol in large-scale brain networks

Anesthesia-induced changes in functional connectivity and cerebral blow flow (CBF) in large-scale brain networks have emerged as key markers of reduced consciousness. However, studies of functional connectivity disagree on which large-scale networks are altered or preserved during anesthesia, making it difficult to find a consensus amount studies. Additionally, pharmacological alterations in CBF could amplify or occlude changes in connectivity due to the shared variance between CBF and connectivity. Here, we used data-driven connectivity methods and multi-modal imaging to investigate shared and unique neural correlates of reduced consciousness for connectivity in large-scale brain networks. Rs-fMRI and CBF data were collected from the same subjects during an awake and deep sedation condition induced by propofol. We measured whole-brain connectivity using the intrinsic connectivity distribution (ICD), a method not reliant on pre-defined seed regions, networks of interest, or connectivity thresholds. The shared and unique variance between connectivity and CBF were investigated. Finally, to account for shared variance, we present a novel extension to ICD that incorporates cerebral blood flow (CBF) as a scaling factor in the calculation of global connectivity, labeled CBF-adjusted ICD). We observed altered connectivity in multiple large-scale brain networks including the default mode (DMN), salience, visual, and motor networks and reduced CBF in the DMN, frontoparietal network, and thalamus. Regional connectivity and CBF were significantly correlated during both the awake and propofol condition. Nevertheless changes in connectivity and CBF between the awake and deep sedation condition were only significantly correlated in a subsystem of the DMN, suggesting that, while there is significant shared variance between the modalities, changes due to propofol are relatively unique. Similar, but less significant, results were observed in the CBF-adjusted ICD analysis, providing additional evidence that connectivity differences were not fully explained by CBF. In conclusion, these results provide further evidence of alterations in large-scale brain networks are associated with reduced consciousness and suggest that different modalities capture unique aspects of these large scale changes.

Consciousness loss during epileptogenesis: implication for VLPO-PnO circuits

There is a growing concern about consciousness loss during epileptic seizures. Understanding neural mechanisms could lead to a better comprehension of cerebral circuit function in the control of consciousness loss in intractable epilepsy. We propose that ventrolateral preoptic area (VLPO)- PnO (nucleus pontis oralis) circuits may serve a major role in the loss of consciousness in drug-refractory epilepsy. Future behavioural and neuroimaging studies are clearly needed to understand the functional connectivity between the VLPO and PnO during loss of consciousness in drug-refractory epilepsy, to greatly prevent unconsciousness in this disorder and improve the quality of life in patients with intractable epilepsy.

Evaluation of Ictal Consciousness in Temporal and Extra Temporal Epilepsy: Observations from a Tertiary Care Hospital in India

Background and Purpose

Differences in consciousness during seizures depend on the location of the seizure onset.

Methods

The present study evaluates ictal consciousness using the ictal consciousness inventory (ICI) in drug refractory mesial temporal (MTLE), neocortical temporal (NTLE) and extra temporal epilepsy (ETLE). This was a cross sectional cohort study with 45 patients with mesial temporal epilepsy, 47 with extra temporal and 11 patients with neocortical temporal epilepsy. The ICI a 20 item questionnaire was used to calculate the scores for level (L, question 1–10) and content (C, question 11–20) of consciousness.

Results

The patients in mesial temporal group had higher ICI-L scores, p = 0.0129 as compared to the extra temporal group, but no difference was observed in the content of consciousness. The ICI-L and C scores were not different in the mesial temporal and the neocortical temporal group (p = 0.53 and 0.65) respectively.

Conclusions

Patients with mesial temporal epilepsy had a higher level of consciousness than the extra temporal group but there was no difference in the content. Also there was no difference in the level and content of consciousness between mesial and the neocortical temporal group.

Neuroimaging somatosensory perception and masking

The specific cortical and subcortical regions involved in conscious perception and masking are uncertain. This study sought to identify brain areas involved in conscious perception of somatosensory stimuli during a masking task using functional magnetic resonance (fMRI) to contrast perceived vs. non-perceived targets. Electrical trains were delivered to the right index finger for targets and to the left index finger for masks. Target intensities were adjusted to compensate for threshold drift. Sham target trials were given in ~10% of the trials, and target stimuli without masks were delivered in one of the five runs (68 trials/run). When healthy dextral adult volunteers (n=15) perceived right hand targets, greater left- than right-cerebral activations were seen with similar patterns across the parietal cortex, thalamus, insula, claustrum, and midbrain. When targets were not perceived, left/right cerebral activations were similar overall. Directly comparing perceived vs. non-perceived stimuli with similar intensities in the masking task revealed predominate activations contralateral to masks. In contrast, activations were greater contralateral to perceived targets if no masks were given or if masks were given but target stimulus intensities were greater for perceived than non-perceived targets. The novel aspects of this study include: 1) imaging of cortical and subcortical activations in healthy humans related to somatosensory perception during a masking task, 2) activations in the human thalamus and midbrain related to perception of stimuli compared to matched non-perceived stimuli, and 3) similar left/right cerebral activation patterns across cortical, thalamic and midbrain structures suggesting interactions across all three levels during conscious perception in humans.

New classification efforts in epilepsy: Opportunities for clinical neurosciences

Classification is truly a scientific endeavor. In recent years, the use of the term in clinical epilepsy has diverged from the purpose of the intellectual process of classification in the sciences. As genetics and molecular biology come into their own, scientific classification may finally come to epilepsy and begin to shed light on the many aspects of brain disorders that are characterized by seizures but which are truly multifaceted disorders and deserve more comprehensive, multidisciplinary approaches than they have received previously. This article is part of a Special Issue entitled "The new approach to classification: Rethinking cognition and behavior in epilepsy".

Hippocampus-associated causal network of structural covariance measuring structural damage progression in temporal lobe epilepsy

In mesial temporal lobe epilepsy (mTLE), the causal relationship of morphometric alterations between hippocampus and the other regions, that is, how the hippocampal atrophy leads to progressive morphometric alterations in the epileptic network regions remains largely unclear. In this study, a causal network of structural covariance (CaSCN) was proposed to map the causal effects of hippocampal atrophy on the network-based morphometric alterations in mTLE. It was hypothesized that if cross-sectional morphometric MRI data could be attributed temporal information, for example, by sequencing the data according to disease progression information, GCA would be a feasible approach for constructing a CaSCN. Based on a large cohort of mTLE patients (n = 108), the hippocampus-associated CaSCN revealed that the hippocampus and the thalamus were prominent nodes exerting causal effects (i.e., GM reduction) on other regions and that the prefrontal cortex and cerebellum were prominent nodes being subject to causal effects. Intriguingly, compensatory increased gray matter volume in the contralateral temporal region and post cingulate cortex were also detected. The method unraveled richer information for mapping network atrophy in mTLE relative to the traditional methods of stage-specific comparisons and structured covariance network. This study provided new evidence on the network spread mechanism in terms of the causal influence of hippocampal atrophy on progressive brain structural alterations in mTLE. Hum Brain Mapp 38:753-766, 2017. © 2016 Wiley Periodicals, Inc.

Synthetic consciousness: the distributed adaptive control perspective

Understanding the nature of consciousness is one of the grand outstanding scientific challenges. The fundamental methodological problem is how phenomenal first person experience can be accounted for in a third person verifiable form, while the conceptual challenge is to both define its function and physical realization. The distributed adaptive control theory of consciousness (DACtoc) proposes answers to these three challenges. The methodological challenge is answered relative to the hard problem and DACtoc proposes that it can be addressed using a convergent synthetic methodology using the analysis of synthetic biologically grounded agents, or quale parsing. DACtoc hypothesizes that consciousness in both its primary and secondary forms serves the ability to deal with the hidden states of the world and emerged during the Cambrian period, affording stable multi-agent environments to emerge. The process of consciousness is an autonomous virtualization memory, which serializes and unifies the parallel and subconscious simulations of the hidden states of the world that are largely due to other agents and the self with the objective to extract norms. These norms are in turn projected as value onto the parallel simulation and control systems that are driving action. This functional hypothesis is mapped onto the brainstem, midbrain and the thalamo-cortical and cortico-cortical systems and analysed with respect to our understanding of deficits of consciousness. Subsequently, some of the implications and predictions of DACtoc are outlined, in particular, the prediction that normative bootstrapping of conscious agents is predicated on an intentionality prior. In the view advanced here, human consciousness constitutes the ultimate evolutionary transition by allowing agents to become autonomous with respect to their evolutionary priors leading to a post-biological Anthropocene.This article is part of the themed issue 'The major synthetic evolutionary transitions'.

Widespread changes in network activity allow non-invasive detection of mesial temporal lobe seizures

Decades of experience with intracranial recordings in patients with epilepsy have demonstrated that seizures can occur in deep cortical regions such as the mesial temporal lobes without showing any obvious signs of seizure activity on scalp electroencephalogram. Predicated on the idea that these seizures are purely focal, currently, the only way to detect these 'scalp-negative seizures' is with intracranial recordings. However, intracranial recordings are only rarely performed in patients with epilepsy, and are almost never performed outside of the context of epilepsy. As such, little is known about scalp-negative seizures and their role in the natural history of epilepsy, their effect on cognitive function, and their association with other neurological diseases. Here, we developed a novel approach to non-invasively identify scalp-negative seizures arising from the mesial temporal lobe based on scalp electroencephalogram network connectivity measures. We identified 25 scalp-negative mesial temporal lobe seizures in 10 patients and obtained control records from an additional 13 patients, all of whom underwent recordings with foramen ovale electrodes and scalp electroencephalogram. Scalp data from these records were used to train a scalp-negative seizure detector, which consisted of a pair of logistic regression classifiers that used scalp electroencephalogram coherence properties as input features. On cross-validation performance, this detector correctly identified scalp-negative seizures in 40% of patients, and correctly identified the side of seizure onset for each seizure detected. In comparison, routine clinical interpretation of these scalp electroencephalograms failed to identify any of the scalp-negative seizures. Among the patients in whom the detector raised seizure alarms, 80% had scalp-negative mesial temporal lobe seizures. The detector had a false alarm rate of only 0.31 per day and a positive predictive value of 75%. Of the 13 control patients, false seizure alarms were raised in only one patient. The fact that our detector specifically recognizes focal mesial temporal lobe seizures based on scalp electroencephalogram coherence features, lends weight to the hypothesis that even focal seizures are a network phenomenon that involve widespread neural connectivity. Our scalp-negative seizure detector has clear clinical utility in patients with temporal lobe epilepsy, and its potential easily translates to other neurological disorders, such as Alzheimer's disease, in which occult mesial temporal lobe seizures are suspected to play a significant role. Importantly, our work establishes a novel approach of using computational approaches to non-invasively detect deep seizure activity, without the need for invasive intracranial recordings.

Optogenetic study of networks in epilepsy

Currently, approximately 30% of patients with epilepsy do not have adequate seizure control. A greater understanding of the underlying mechanisms by which seizures start or propagate could lead to new therapeutic strategies. The recent development of optogenetics, because of its unprecedented precision for controlling activity within distinct neuronal populations, has revolutionized neuroscience, including epilepsy research. This Review discusses recent breakthroughs made with optogenetics in epilepsy research. These breakthroughs include new insights into the key roles that different cell types play in mediating seizures as well as in the development of epilepsy. Subsequently, we discuss how targeting different brain regions and cell populations has opened up the possibility of highly specific therapies that can stop seizures on demand. Finally, we illustrate how combining newly available neuroscience tools with whole-brain imaging techniques will allow researchers to understand better the spread of seizures on a network level. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

From unwitnessed fatality to witnessed rescue: Nonpharmacologic interventions in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) risk reduction remains a critical aim in epilepsy care. To date, only aggressive medical and surgical efforts to control seizures have been demonstrated to be of benefit. Incomplete understanding of SUDEP mechanisms limits the development of more specific interventions. Periictal cardiorespiratory dysfunction is implicated in SUDEP; postictal electroencephalography (EEG) suppression, coma, and immobility may also play a role. Nocturnal supervision is protective against SUDEP, presumably by permitting intervention in the case of a life-threatening event. Resuscitative efforts were implemented promptly in near-SUDEP cases but delayed in SUDEP deaths in the Mortality in Epilepsy Monitoring Unit Study (MORTEMUS) study. Nursing interventions--including repositioning, oral suctioning, and oxygen administration--reduce seizure duration, respiratory dysfunction, and EEG suppression in the epilepsy monitoring unit (EMU), but have not been studied in outpatients. Cardiac pacemakers or cardioverter-defibrillator devices may be of benefit in a few select individuals. A role for implantable neurostimulators has not yet been established. Seizure detection devices, including those that monitor generalized tonic-clonic seizure-associated movements or cardiorespiratory parameters, may provide a means to permit timely periictal intervention. However, these and other devices, such as antisuffocation pillows, have not been adequately investigated with respect to SUDEP prevention.

Are There Levels of Consciousness?

The notion of a level of consciousness is a key construct in the science of consciousness. Not only is the term employed to describe the global states of consciousness that are associated with post-comatose disorders, epileptic absence seizures, anaesthesia, and sleep, it plays an increasingly influential role in theoretical and methodological contexts. However, it is far from clear what precisely a level of consciousness is supposed to be. This paper argues that the levels-based framework for conceptualizing global states of consciousness is untenable and develops in its place a multidimensional account of global states.

The Structural Connectome of the Human Central Homeostatic Network

Homeostatic adaptations to stress are regulated by interactions between the brainstem and regions of the forebrain, including limbic sites related to respiratory, autonomic, affective, and cognitive processing. Neuroanatomic connections between these homeostatic regions, however, have not been thoroughly identified in the human brain. In this study, we perform diffusion spectrum imaging tractography using the MGH-USC Connectome MRI scanner to visualize structural connections in the human brain linking autonomic and cardiorespiratory nuclei in the midbrain, pons, and medulla oblongata with forebrain sites critical to homeostatic control. Probabilistic tractography analyses in six healthy adults revealed connections between six brainstem nuclei and seven forebrain regions, several over long distances between the caudal medulla and cerebral cortex. The strongest evidence for brainstem-homeostatic forebrain connectivity in this study was between the brainstem midline raphe and the medial temporal lobe. The subiculum and amygdala were the sampled forebrain nodes with the most extensive brainstem connections. Within the human brainstem-homeostatic forebrain connectome, we observed that a lateral forebrain bundle, whose connectivity is distinct from that of rodents and nonhuman primates, is the primary conduit for connections between the brainstem and medial temporal lobe. This study supports the concept that interconnected brainstem and forebrain nodes form an integrated central homeostatic network (CHN) in the human brain. Our findings provide an initial foundation for elucidating the neuroanatomic basis of homeostasis in the normal human brain, as well as for mapping CHN disconnections in patients with disorders of homeostasis, including sudden and unexpected death, and epilepsy.

Neurostimulation to improve level of consciousness in patients with epilepsy

When drug-resistant epilepsy is poorly localized or surgical resection is contraindicated, current neurostimulation strategies such as deep brain stimulation and vagal nerve stimulation can palliate the frequency or severity of seizures. However, despite medical and neuromodulatory therapy, a significant proportion of patients continue to experience disabling seizures that impair awareness, causing disability and risking injury or sudden unexplained death. We propose a novel strategy in which neuromodulation is used not only to reduce seizures but also to ameliorate impaired consciousness when the patient is in the ictal and postictal states. Improving or preventing alterations in level of consciousness may have an effect on morbidity (e.g., accidents, drownings, falls), risk for death, and quality of life. Recent studies may have elucidated underlying networks and mechanisms of impaired consciousness and yield potential novel targets for neuromodulation. The feasibility, benefits, and pitfalls of potential deep brain stimulation targets are illustrated in human and animal studies involving minimally conscious/vegetative states, movement disorders, depth of anesthesia, sleep-wake regulation, and epilepsy. We review evidence that viable therapeutic targets for impaired consciousness associated with seizures may be provided by key nodes of the consciousness system in the brainstem reticular activating system, hypothalamus, basal ganglia, thalamus, and basal forebrain.

Seizures and brain regulatory systems: consciousness, sleep, and autonomic systems

Research into the physiologic underpinnings of epilepsy has revealed reciprocal relationships between seizures and the activity of several regulatory systems in the brain. This review highlights recent progress in understanding and using the relationships between seizures and the arousal or consciousness system, the sleep-wake and associated circadian system, and the central autonomic network.

Impaired Serotonergic Brainstem Function during and after Seizures

Impaired breathing, cardiac function, and arousal during and after seizures are important causes of morbidity and mortality. Previous work suggests that these changes are associated with depressed brainstem function in the ictal and post-ictal periods. Lower brainstem serotonergic systems are postulated to play an important role in cardiorespiratory changes during and after seizures, whereas upper brainstem serotonergic and other systems regulate arousal. However, direct demonstration of seizure-associated neuronal activity changes in brainstem serotonergic regions has been lacking. Here, we performed multiunit and single-unit recordings from medullary raphe and midbrain dorsal raphe nuclei in an established rat seizure model while measuring changes in breathing rate and depth as well as heart rate. Serotonergic neurons were identified by immunohistochemistry. Respiratory rate, tidal volume, and minute ventilation were all significantly decreased during and after seizures in this model. We found that population firing of neurons in the medullary and midbrain raphe on multiunit recordings was significantly decreased during the ictal and post-ictal periods. Single-unit recordings from identified serotonergic neurons in the medullary raphe revealed highly consistently decreased firing during and after seizures. In contrast, firing of midbrain raphe serotonergic neurons was more variable, with a mixture of increases and decreases. The markedly suppressed firing of medullary serotonergic neurons supports their possible role in simultaneously impaired cardiorespiratory function in seizures. Decreased arousal likely arises from depressed population activity of several neuronal pools in the upper brainstem and forebrain. These findings have important implications for preventing morbidity and mortality in people living with epilepsy.

SIGNIFICANCE STATEMENT

Seizures often cause impaired breathing, cardiac dysfunction, and loss of consciousness. The brainstem and, specifically, brainstem serotonin neurons are thought to play an important role in controlling breathing, cardiac function, and arousal. We used an established rat seizure model to study the overall neuronal activity in the brainstem as well as firing of specific serotonin neurons while measuring cardiorespiratory function. Our results demonstrated overall decreases in brainstem neuronal activity and marked downregulation of lower brainstem serotonin neuronal firing in association with decreased breathing and heart rate during and after seizures. These findings point the way toward new treatments to augment brainstem function and serotonin, aiming to prevent seizure complications and reduce morbidity and mortality in people living with epilepsy.

Influence of vigilance state on physiological consequences of seizures and seizure-induced death in mice

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. SUDEP occurs more commonly during nighttime sleep. The details of why SUDEP occurs at night are not well understood. Understanding why SUDEP occurs at night during sleep might help to better understand why SUDEP occurs at all and hasten development of preventive strategies. Here we aimed to understand circumstances causing seizures that occur during sleep to result in death. Groups of 12 adult male mice were instrumented for EEG, EMG, and EKG recording and subjected to seizure induction via maximal electroshock (MES) during wakefulness, nonrapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Seizure inductions were performed with concomitant EEG, EMG, and EKG recording and breathing assessment via whole body plethysmography. Seizures induced via MES during sleep were associated with more profound respiratory suppression and were more likely to result in death. Despite REM sleep being a time when seizures do not typically occur spontaneously, when seizures were forced to occur during REM sleep, they were invariably fatal in this model. An examination of baseline breathing revealed that mice that died following a seizure had increased baseline respiratory rate variability compared with those that did not die. These data demonstrate that sleep, especially REM sleep, can be a dangerous time for a seizure to occur. These data also demonstrate that there may be baseline respiratory abnormalities that can predict which individuals have higher risk for seizure-induced death.

Subjective and objective characteristics of altered consciousness during epileptic seizures

BACKGROUND

Conscious states are inner states and processes of awareness. These states are by definition subjective.

METHODS

We analyzed subjective and objective characteristics of alteration of consciousness (AOC) during epileptic seizures, including its involvement in both the level of awareness and subjective content of consciousness. We evaluated AOC using the Consciousness Seizure Scale, the Ictal Consciousness Inventory, and a new structured survey developed by our group: the Seizure Perception Survey, which incorporates patients' subjective experiences before and after they watch a video-electroencephalographic recording of their own seizure.

RESULTS

We included 35 patients (105 seizures) with drug-resistant epilepsy. Most seizures caused profound AOC. The content of consciousness was lower during temporal seizures with profound AOC. We uncovered a correlation between the subjective perception and objective duration of a seizure using the Seizure Perception Survey regarding memory; the patients had a better recall of ictal onset during wakefulness regardless of the epileptogenic zone, laterality, or magnitude of AOC. Nonetheless, the recovery of memory at the end of a seizure took more time in patients who showed greater AOC, less vivid content of consciousness, or a longer seizure. For 85% of the patients, this was the first time they were able to view their own seizures. The majority of the patients requested to view them again because this procedure allowed them to compare the recordings with their own memories and emotions during a seizure and to verify the real duration of the seizure.

DISCUSSION

Alteration of consciousness is one of the most dramatic clinical manifestations of epilepsy. Usually, practitioners or relatives assume that the patients with AOC may not have any knowledge on their seizures. In this study, however, we found that most patients with AOC had a fairly accurate perception of the duration of a seizure and retained their memory of ictal onset. In contrast, for the majority of the patients, watching their own seizure was an extremely positive experience, and most patients stated that they were surprised as well as glad to view what really happened, without expressing negative opinions. Inclusion of subjective characteristics of AOC into the analysis yielded complete assessment of various dimensions of consciousness and therefore allowed us to gain a more detailed understanding of consciousness.

Speed of recovery from disorientation may predict the treatment outcome of electroconvulsive therapy (ECT) in elderly patients with major depression

BACKGROUND

No study has previously investigated whether the speed of recovery from disorientation in the post-ictal period may predict the short-term treatment outcome of electroconvulsive therapy (ECT).

METHODS

This longitudinal cohort study included 57 elderly patients with unipolar or bipolar major depression, aged 60-85 years, treated with formula-based ECT. Treatment outcome was assessed weekly during the ECT course using the 17-item Hamilton Rating Scale for Depression (HRSD17). The post-ictal reorientation time (PRT) was assessed at the first and third treatments.

RESULTS

Longer PRTs at the first and third treatments predicted a more rapid decline and a lower end-point in continuous HRSD17 scores (p=0.002 and 0.019, respectively). None of the patients who recovered from disorientation in less than 5 min met the remission criterion, defined as an HRSD17 score of 7 or less. A greater increment in stimulus dosage from the first to the third ECT session rendered a smaller relative decline in PRT (p<0.001).

LIMITATIONS

The limited number of subjects may reduce the generalizability of the findings.

CONCLUSIONS

The speed of recovery from disorientation at the first and third sessions seems to be a predictor of the treatment outcome of formula-based ECT, at least in elderly patients with major depression. It remains to be clarified how the PRT may be utilized to guide stimulus dosing.

Moving into the wide clinical spectrum of consciousness disorders: Pearls, perils and pitfalls

The last few years have been characterized by a growing interest of the medical and scientific world for the field of consciousness and its related disorders. Medically speaking, consciousness can be defined as the state of awareness of self and environment and the alertness to external stimulation, besides responsiveness to inner need. Transient loss of consciousness can be due to alterations in cerebral blood flow leading to fainting or syncope, migraine, metabolic dysfunctions, unexpected intracranial pressure increases, epileptic seizures, and sleep disorders. Chronic disorders of consciousness are a tragic success of high-technology treatment, in an attempt to maintain or reestablish brain function, which is to be considered as the main goal of therapeutics. Management of vegetative or a minimally conscious state individuals involves charily getting the right diagnosis with an evidence-based prognosis, also taking into account the medical, ethical, and legal key factors of the ideal treatment. This paper is aimed at exploring the wide spectrum of consciousness disorders and their clinical differential diagnosis, with particular regards to those with a negative impact on patient and their caregiver quality of life, including epilepsy, sleep disorders, and vegetative/minimally conscious state.

Human bedside evaluation versus automatic responsiveness testing in epilepsy (ARTiE)

Evaluation of behavioral impairment during epileptic seizures is critical for medical decision making, including accurate diagnosis, recommendations for driving, and presurgical evaluation. We investigated the quality of behavioral testing during inpatient video-electroencephalography (EEG) monitoring at an established epilepsy center, and introduce a technical innovation that may improve clinical care. We retrospectively reviewed video-EEG data from 152 seizures in 33 adult or pediatric patients admitted for video-EEG monitoring. Behavioral testing with questions or commands was performed in only 50% of seizures ictally, 73% of seizures postictally, and 80% with either ictal or postictal testing combined. Furthermore, the questions or commands were highly inconsistent and were performed by nonmedical personnel in about one fourth of cases. In an effort to improve this situation we developed and here introduce Automatic Responsiveness Testing in Epilepsy (ARTiE), a series of video-recorded behavioral tasks automatically triggered to play in the patient's room by computerized seizure detection. In initial technical testing using prerecorded or live video-EEG data we found that ARTiE is initiated reliably by automatic seizure detection. With additional clinical testing we hope that ARTiE will succeed in providing comprehensive and reliable behavioral evaluation during seizures for people with epilepsy to greatly improve their clinical care.

Optogenetic stimulation of cholinergic brainstem neurons during focal limbic seizures: Effects on cortical physiology

Focal temporal lobe seizures often cause impaired cortical function and loss of consciousness. Recent work suggests that the mechanism for depressed cortical function during focal seizures may depend on decreased subcortical cholinergic arousal, which leads to a sleep-like state of cortical slow-wave activity. To test this hypothesis, we sought to directly activate subcortical cholinergic neurons during focal limbic seizures to determine the effects on cortical function. Here we used an optogenetic approach to selectively stimulate cholinergic brainstem neurons in the pedunculopontine tegmental nucleus during focal limbic seizures induced in a lightly anesthetized rat model. We found an increase in cortical gamma activity and a decrease in delta activity in response to cholinergic stimulation. These findings support the mechanistic role of reduced subcortical cholinergic arousal in causing cortical dysfunction during seizures. Through further work, electrical or optogenetic stimulation of subcortical arousal networks may ultimately lead to new treatments aimed at preventing cortical dysfunction during seizures.

Validation of the Generalized Anxiety Disorder-7 (GAD-7) among Chinese people with epilepsy

OBJECTIVE

To validate the Chinese version of the Generalized Anxiety Disorder-7 (GAD-7) in Chinese people with epilepsy (PWE).

METHODS

A consecutive cohort of PWE from the West China Hospital was recruited. Each patient received a psychiatric evaluation comprising the Mini International Neuropsychiatric Interview (MINI) and the GAD-7. Demographic and clinical characteristics were collected. Cronbach's α coefficient was calculated and receiver operating curve (ROC) analysis was conducted.

RESULTS

A total of 213 PWE completed the psychiatric evaluation. The GAD-7 was easily understood and quickly completed by all participants. Fifty patients (23.5%) had GAD according to the MINI criteria. Cronbach's α coefficient for the GAD-7 was 0.888. ROC analysis showed an area under the curve of 0.974 (95% CI=0.956-0.993). At a cut-off score of >6, the GAD-7 achieved the largest Youden index of 0.854 with a sensitivity of 94%, a specificity of 91.4%, a positive predictive value of 77% and a negative predictive value of 98%.

SIGNIFICANCE

The Chinese version of the GAD-7 is a valuable tool for screening for GAD in Chinese PWE.

Cessation of gamma activity in the dorsomedial nucleus associated with loss of consciousness during focal seizures

RATIONALE

Impaired consciousness during seizures may be mediated by ictal propagation to the thalamus. Functions of individual thalamic nuclei with respect to consciousness, however, are largely unknown. The dorsomedial (DM) nucleus of the thalamus likely plays a role in arousal and cognition. We propose that alterations of firing patterns within the DM nucleus contribute to impaired arousal during focal seizures.

METHODS

Electroencephalograph data were collected from electrodes within the left DM thalamus and midcingulate cortex (MCC) in a patient undergoing seizure monitoring. Spectral power was computed across ictal states (preictal, ictal, and postictal) and level of consciousness (stupor/sleep vs. awake) in the DM nucleus and MCC.

RESULTS

Eighty-seven seizures of multifocal left frontal and temporal onsets were analyzed, characterized by loss of consciousness. At baseline, the left DM nucleus demonstrated rhythmic bursts of gamma activity, most frequently and with greatest amplitude during wakefulness. This activity ceased as ictal discharges spread to the MCC, and consciousness was impaired, and it recurred at the end of each seizure as awareness was regained. The analysis of gamma (30-40Hz) power demonstrated that when seizures occurred during wakefulness, there was lower DM ictal power (p<0.0001) and higher DM postictal power (p<0.0001) relative to the preictal epoch. This spectral pattern was not evident within the MCC or when seizures occurred during sleep.

CONCLUSIONS

Data revealed a characteristic pattern of DM gamma bursts during wakefulness, which disappeared during partial seizures associated with impaired consciousness. The findings are consistent with studies suggesting that the DM nucleus participates in cognition and arousal.

Respiratory pathophysiology with seizures and implications for sudden unexpected death in epilepsy

SUMMARY

There is increasing evidence that periictal respiratory disturbances are an important contributor to the pathophysiological changes leading to sudden unexpected death in epilepsy (SUDEP). In patients with SUDEP occurring in epilepsy monitoring units, respiratory disturbances occurred early in the postictal period and frequently preceded terminal bradycardia and asystole. Periictal hypoxemia and hypercapnia are observed in about one-third of patients undergoing video-EEG telemetry. Pulmonary edema is frequently observed at autopsy in cases of SUDEP and may be relevant as a contributing cause in a subset of SUDEP. Animal studies support the notion that periictal respiratory disturbances are crucial to the pathophysiology of SUDEP. Serotonergic neurons modulate the excitability of the neuronal network generating the respiratory rhythm. Ictal and periictal impairment of serotonergic and glutaminergic neurons involved in the arousal system may also predispose to SUDEP by impeding the patient's ability to reposition the head and facilitate ventilation after a seizure. Periictal functional impairment of serotonergic neurons seems to be important in the pathophysiology of SUDEP and a potential target for pharmacotherapy aimed at SUDEP risk reduction.

Seizure reporting technologies for epilepsy treatment: A review of clinical information needs and supporting technologies

This review surveys current seizure detection and classification technologies as they relate to aiding clinical decision-making during epilepsy treatment. Interviews and data collected from neurologists and a literature review highlighted a strong need for better distinguishing between patients exhibiting generalized and partial seizure types as well as achieving more accurate seizure counts. This information is critical for enabling neurologists to select the correct class of antiepileptic drugs (AED) for their patients and evaluating AED efficiency during long-term treatment. In our questionnaire, 100% of neurologists reported they would like to have video from patients prior to selecting an AED during an initial consultation. Presently, only 30% have access to video. In our technology review we identified that only a subset of available technologies surpassed patient self-reporting performance due to high false positive rates. Inertial seizure detection devices coupled with video capture for recording seizures at night could stand to address collecting seizure counts that are more accurate than current patient self-reporting during day and night time use.

Slow Spatial Recruitment of Neocortex during Secondarily Generalized Seizures and Its Relation to Surgical Outcome

Understanding the spatiotemporal dynamics of brain activity is crucial for inferring the underlying synaptic and nonsynaptic mechanisms of brain dysfunction. Focal seizures with secondary generalization are traditionally considered to begin in a limited spatial region and spread to connected areas, which can include both pathological and normal brain tissue. The mechanisms underlying this spread are important to our understanding of seizures and to improve therapies for surgical intervention. Here we study the properties of seizure recruitment-how electrical brain activity transitions to large voltage fluctuations characteristic of spike-and-wave seizures. We do so using invasive subdural electrode arrays from a population of 16 patients with pharmacoresistant epilepsy. We find an average delay of ∼30 s for a broad area of cortex (8 × 8 cm) to be recruited into the seizure, at an estimated speed of ∼4 mm/s. The spatiotemporal characteristics of recruitment reveal two categories of patients: one in which seizure recruitment of neighboring cortical regions follows a spatially organized pattern consistent from seizure to seizure, and a second group without consistent spatial organization of activity during recruitment. The consistent, organized recruitment correlates with a more regular, compared with small-world, connectivity pattern in simulation and successful surgical treatment of epilepsy. We propose that an improved understanding of how the seizure recruits brain regions into large amplitude voltage fluctuations provides novel information to improve surgical treatment of epilepsy and highlights the slow spread of massive local activity across a vast extent of cortex during seizure.

Frequency-Specific Alterations of Local Synchronization in Idiopathic Generalized Epilepsy

Recurrently and abnormally hypersynchronous discharge is a striking feature of idiopathic generalized epilepsy (IGE). Resting-state functional magnetic resonance imaging has revealed aberrant spontaneous brain synchronization, predominately in low-frequency range (<0.1 Hz), in individuals with IGE. Little is known, however, about these changes in local synchronization across different frequency bands. We examined alterations to frequency-specific local synchronization in terms of spontaneous blood oxygen level-dependent (BOLD) fluctuations across 5 bands, spanning 0 to 0.25 Hz. Specifically, we compared brain activity in a large cohort of IGE patients (n = 86) to age- and sex-matched normal controls (n = 86). IGE patients showed decreased local synchronization in low frequency (<0.073 Hz), primarily in the default mode network (DMN). IGE patients also exhibited increased local synchronization in high-frequency (>0.073 Hz) in a "conscious perception network," which is anchored by the pregenual and dorsal anterior cingulate cortex, as well as the bilateral insular cortices, possibly contributing to impaired consciousness. Furthermore, we found frequency-specific alternating local synchronization in the posterior portion of the DMN relative to the anterior part, suggesting an interaction between the disease and frequency bands. Importantly, the aberrant high-frequency local synchronization in the middle cingulate cortex was associated with disease duration, thus linking BOLD frequency changes to disease severity. These findings provide an overview of frequency-specific local synchronization of BOLD fluctuations, and may be helpful in uncovering abnormal synchronous neuronal activity in patients with IGE at specific frequency bands.

Decreased subcortical cholinergic arousal in focal seizures

Impaired consciousness in temporal lobe seizures has a major negative impact on quality of life. The prevailing view holds that this disorder impairs consciousness by seizure spread to the bilateral temporal lobes. We propose instead that seizures invade subcortical regions and depress arousal, causing impairment through decreases rather than through increases in activity. Using functional magnetic resonance imaging in a rodent model, we found increased activity in regions known to depress cortical function, including lateral septum and anterior hypothalamus. Importantly, we found suppression of intralaminar thalamic and brainstem arousal systems and suppression of the cortex. At a cellular level, we found reduced firing of identified cholinergic neurons in the brainstem pedunculopontine tegmental nucleus and basal forebrain. Finally, we used enzyme-based amperometry to demonstrate reduced cholinergic neurotransmission in both cortex and thalamus. Decreased subcortical arousal is a critical mechanism for loss of consciousness in focal temporal lobe seizures.

Altered resting state functional network connectivity in children absence epilepsy

Altered functional connectivity has been associated with the influence of epileptic activity. Abnormalities in connectivity, particularly in dorsal attention (DAN), salience (SN) and default mode (DMN) networks, might contribute to the loss of consciousness during seizures and cognitive deficits in patients with children absence epilepsy (CAE). The objective of the present study was to identify whether the functional network connectivity (FNC) is changed between patients with CAE and healthy controls. Using independent component analysis, twelve resting state networks (RSNs) were identified in resting state functional magnetic resonance imaging data sets in eighteen CAE patients and twenty-one healthy controls. Analyses of the group differences in FNC strength were conducted, controlling for age and gender effects. The findings showed that some functional networks were clustered into two subgroups, correlated within subgroups and antagonized with each other. Compared with the controls, patients with CAE demonstrated abnormal FNC strength among three networks: DMN, DAN and SN. In addition, the antagonism of two subgroups was altered. These results might reflect the underlying neuronal functional impairment or altered integration among these RSNs in CAE, suggesting that the abnormal functional connectivity is likely to imply the pathological mechanism associated with the accumulative influence of epileptic activity. These findings contribute to the understanding of the behavior abnormality in CAE, such as disturbed executive and attentional functions and the loss of consciousness during absence seizures.

Identifying Corticothalamic Network Epicenters in Patients with Idiopathic Generalized Epilepsy

BACKGROUND AND PURPOSE

Corticothalamic networks are considered core pathologic substrates for idiopathic generalized epilepsy; however, the predominant epileptogenic epicenters within these networks are still largely unknown. The current study aims to identify these epicenters by resting-state functional connectivity.

MATERIALS AND METHODS

To identify epicenters within the corticothalamic networks in idiopathic generalized epilepsy, we retrospectively studied a large cohort of patients with this condition (n = 97) along with healthy controls (n = 123) by resting-state functional MR imaging. The thalamus was functionally divided into subregions corresponding to distinct cortical lobes for 5 parallel corticothalamic networks. The functional connectivity between each voxel in the cortical lobe and the corresponding thalamic subregion was calculated, and functional connectivity strength was used to evaluate the interconnectivity of voxels in the cortex and thalamus.

RESULTS

The projection of 5 cortical lobes to the thalamus is consistent with previous histologic findings in humans. Compared with controls, patients with idiopathic generalized epilepsy showed increased functional connectivity strength in 4 corticothalamic networks: 1) the supplementary motor area, pulvinar, and ventral anterior nucleus in the prefrontal-thalamic network; 2) the premotor cortex and ventrolateral nucleus in motor/premotor-thalamic networks; 3) the visual cortex, posterior default mode regions, and pulvinar in parietal/occipital-thalamic networks; and 4) the middle temporal gyrus in the temporal-thalamic network.

CONCLUSIONS

Several key nodes were distinguished in 4 corticothalamic networks. The identification of these epicenters refines the corticothalamic network theory and provides insight into the pathophysiology of idiopathic generalized epilepsy.

Ictal Generalized EEG Attenuation (IGEA) and hypopnea in a child with occipital type 1 cortical dysplasia - Is it a biomarker for SUDEP?

An interesting association of ictal hypopnea and ictal generalized EEG attenuation (IGEA) as possible marker of sudden unexpected death in epilepsy (SUDEP) is reported. We describe a 5-years-old girl with left focal seizures with secondary generalization due to right occipital cortical dysplasia presenting with ictal hypopnea and IGEA. She had repeated episodes of the ictal apnoea in the past requiring ventilator support and intensive care unit (ICU) admission during episodes of status epilepticus. The IGEA lasted for 0.26-4.68 seconds coinciding with the ictal hypopnea during which both clinical seizure and electrical epileptic activity stopped. Review of literature showed correlation between post-ictal apnoea and post ictal generalized EEG suppression and increased risk for SUDEP. The report adds to the growing body of literature on peri-ictal apnea, about its association with IGEA might be considered as a marker for SUDEP. She is seizure free for 4 months following surgery.

A critical evaluation of the gamma-hydroxybutyrate (GHB) model of absence seizures

Typical absence seizures (ASs) are nonconvulsive epileptic events which are commonly observed in pediatric and juvenile epilepsies and may be present in adults suffering from other idiopathic generalized epilepsies. Our understanding of the pathophysiological mechanisms of ASs has been greatly advanced by the availability of genetic and pharmacological models, in particular the γ-hydroxybutyrate (GHB) model which, in recent years, has been extensively used in studies in transgenic mice. GHB is an endogenous brain molecule that upon administration to various species, including humans, induces not only ASs but also a state of sedation/hypnosis. Analysis of the available data clearly indicates that only in the rat does there exist a set of GHB-elicited behavioral and EEG events that can be confidently classified as ASs. Other GHB activities, particularly in mice, appear to be mostly of a sedative/hypnotic nature: thus, their relevance to ASs requires further investigation. At the molecular level, GHB acts as a weak GABA-B agonist, while the existence of a GHB receptor remains elusive. The pre- and postsynaptic actions underlying GHB-elicited ASs have been thoroughly elucidated in thalamus, but little is known about the cellular/network effects of GHB in neocortex, the other brain region involved in the generation of ASs.

BOLD responses related to focal spikes and widespread bilateral synchronous discharges generated in the frontal lobe

OBJECTIVE

To investigate whether specific frontal regions have a tendency to generate widespread bilateral synchronous discharges (WBSDs) and others focal spikes and to determine the regions most involved when WBSDs occur; to assess the relationships between the extent of electroencephalography (EEG) discharges and the extent of metabolic changes measured by EEG/functional magnetic resonance imaging (fMRI).

METHODS

Thirty-seven patients with interictal epileptic discharges (IEDs) with frontocentral predominance underwent EEG/fMRI. Patients were divided into a Focal (20 patients) group with focal frontal spikes and a WBSD group (17 patients). Maps of hemodynamic responses related to IEDs were compared between the two groups.

RESULTS

The mean number ± SD of IEDs in the Focal group was 137.5 ± 38.1 and in the WBSD group, 73.5 ± 16.6 (p = 0.07). The volume of hemodynamic responses in the WBSD group was significantly larger than in the Focal group (mean, 243.3 ± 41.1 versus 114.8 ± 27.4 cm(3), p = 0.01). Maximum hemodynamic responses occurred in both groups in the following regions: dorsolateral prefrontal, mesial prefrontal, cingulate, and supplementary motor cortices. Maxima in premotor and motor cortex, frontal operculum, frontopolar, and orbitofrontal regions were found only in the Focal group, and maxima in thalamus and caudate only occurred in the WBSD group. Thalamic responses were significantly more common in the WBSD group (14/17) than in the Focal group (7/20), p = 0.004. Deactivation in the default mode network was significantly more common in the WBSD group (14/17) than in the Focal group (10/20), p = 0.04.

SIGNIFICANCE

The spatial distribution and extent of blood oxygen level-dependent (BOLD) responses correlate well with electrophysiologic changes. Focal frontal spikes and WBSDs are not region specific in the frontal lobe, and the same frontal region can generate focal and generalized discharges. This suggests that widespread discharges reflect widespread epileptogenicity rather than a focal discharge located in a region favorable to spreading. The thalamus plays an important role in bilateral synchronization.

Thalamic stimulation to improve level of consciousness after seizures: evaluation of electrophysiology and behavior

OBJECTIVE

Understanding the neural mechanisms that support human consciousness is an important frontier in neuroscience and medicine. We previously developed a rodent model of temporal lobe seizures that recapitulates the human electroencephalography (EEG) signature of ictal and postictal neocortical slow waves associated with behavioral impairments in level of consciousness. The mechanism of slow-wave production in epilepsy may involve suppression of the subcortical arousal systems including the brainstem and intralaminar thalamic nuclei. We hypothesized that intralaminar thalamic stimulation may lead to electrophysiologic and functional rescue from postictal slow waves and behavioral arrest.

METHODS

We electrically stimulated the central lateral thalamic nucleus (a member of the intralaminar nuclei) under anesthesia and after electrically induced hippocampal seizures in anesthetized and in awake-behaving animal model preparations.

RESULTS

We demonstrated a proof-of-principle restoration of electrophysiologic and behavioral measures of consciousness by stimulating the intralaminar thalamic nuclei after seizures. We measured decreased cortical slow waves and increased desynchronization and multiunit activity in the cortex with thalamic stimulation following seizures. Functionally, thalamic stimulation produced resumption of exploratory behaviors in the postictal state.

SIGNIFICANCE

Targeting of nodes in the neural circuitry of consciousness has important medical implications. Impaired consciousness with epilepsy has dangerous consequences including decreased school/work performance, social stigmatization, and impaired airway protection. These data suggest a novel therapeutic approach for restoring consciousness after seizures. If paired with responsive neurostimulation, this may allow rapid implementation to improve level of consciousness in patients with epilepsy.

Mapping epileptic activity: sources or networks for the clinicians?

Epileptic seizures of focal origin are classically considered to arise from a focal epileptogenic zone and then spread to other brain regions. This is a key concept for semiological electro-clinical correlations, localization of relevant structural lesions, and selection of patients for epilepsy surgery. Recent development in neuro-imaging and electro-physiology and combinations, thereof, have been validated as contributory tools for focus localization. In parallel, these techniques have revealed that widespread networks of brain regions, rather than a single epileptogenic region, are implicated in focal epileptic activity. Sophisticated multimodal imaging and analysis strategies of brain connectivity patterns have been developed to characterize the spatio-temporal relationships within these networks by combining the strength of both techniques to optimize spatial and temporal resolution with whole-brain coverage and directional connectivity. In this paper, we review the potential clinical contribution of these functional mapping techniques as well as invasive electrophysiology in human beings and animal models for characterizing network connectivity.

Study on the Relationships between Intrinsic Functional Connectivity of the Default Mode Network and Transient Epileptic Activity

Rationale: Simultaneous recording of electroencephalogram and functional MRI (EEG–fMRI) is a powerful tool for localizing epileptic networks via the detection of hemodynamic changes correlated with interictal epileptic discharges (IEDs). fMRI can be used to study the long-lasting effect of epileptic activity by assessing stationary functional connectivity during the resting-state period [especially, the connectivity of the default mode network (DMN)]. Temporal lobe epilepsy (TLE) and idiopathic generalized epilepsy (IGE) are associated with low responsiveness and disruption of DMN activity. A dynamic functional connectivity approach might enable us to determine the effect of IEDs on DMN connectivity and to better understand the correlation between DMN connectivity changes and altered consciousness.

Method: We studied dynamic changes in DMN intrinsic connectivity and their relation to IEDs. Six IGE patients (with generalized spike and slow-waves) and 6 TLE patients (with unilateral left temporal spikes) were included. Functional connectivity before, during, and after IEDs was estimated using a sliding window approach and compared with the baseline period.

Results: No dependence on window size was observed. The baseline DMN connectivity was decreased in the left hemisphere (ipsilateral to the epileptic focus) in TLEs and was less strong but remained bilateral in IGEs. We observed an overall increase in DMN intrinsic connectivity prior to the onset of IEDs in both IGEs and TLEs. After IEDs in TLEs, we found that DMN connectivity increased before it returned to baseline values. Most of the DMN regions with increased connectivity before and after IEDs were lateralized to the left hemisphere in TLE (i.e., ipsilateral to the epileptic focus).

Conclusion: Results suggest that DMN connectivity may facilitate IED generation and may be affected at the time of the IED. However, these results need to be confirmed in a larger independent cohort.