Impaired consciousness in epilepsy

Disrupted functional network in patients with temporal lobe epilepsy with impaired alertness

Cognitive impairment is common in patients with temporal lobe epilepsy (TLE). Alertness is an important subfunction of cognition, but it is poorly understood in TLE. We hypothesized that disruptions to underlying brain networks may affect alertness in patients with TLE. Patients with unilateral TLE were grouped into low-alertness and high-alertness groups, and they were matched with healthy controls (HCs) (n = 20 each). Functional magnetic resonance imaging (fMRI) was used to construct functional brain networks, and graph theory was used to identify topological parameters of the networks. At the global level, patients with low alertness had networks with less small-worldness and less normalized clustering than HCs. At the nodal level, patients with low alertness exhibited decreased centrality of the bilateral parahippocampal gyrus compared with HCs and increased centrality of the right postcentral gyrus compared with patients with high alertness. This study reveals a decreased separation, tending toward randomization, of the functional network in patients with TLE with impaired alertness. Our results also suggest that the parahippocampal gyrus may contribute to impaired alertness and the right postcentral gyrus plays an important role in the modulation of alertness in patients with TLE.

Transcriptomic Characterization of the Human Insular Cortex and Claustrum

The insular cortex has been linked to a multitude of functions. In contrast, the nearby claustrum is a densely connected subcortical region with unclear function. To view the insula-claustrum region from the molecular perspective we analyzed the transcriptomic profile of these areas in six adult and four fetal human brains. We identified marker genes with specific expression and performed transcriptome-wide tests for enrichment of biological processes, molecular functions, and cellular components. In addition, specific insular and claustral expression of genes pertaining to diseases, addiction, and depression was tested. At the anatomical level, we used brain-wide analyses to determine the specificity of our results and to determine the transcriptomic similarity of the insula-claustrum region. We found UCMA to be the most significantly enriched gene in the insular cortex and confirmed specific expression of NR4A2, NTNG2, and LXN in the claustrum. Furthermore, the insula was found to have enriched expression of genes associated with mood disorders, learning, cardiac muscle contraction, oxygen transport, glutamate and dopamine signaling. Specific expression in the claustrum was enriched for genes pertaining to human immunodeficiency virus (HIV), severe intellectual disability, epileptic encephalopathy, intracellular transport, spine development, and macroautophagy. We tested for enrichment of genes related to addiction and depression, but they were generally not highly specific to the insula-claustrum region. Exceptions include high insular expression of genes linked to cocaine abuse and genes associated with ever smoking in the claustrum. Brain-wide, we find that markers of the adult claustrum are most specifically expressed in the fetal and adult insula. Altogether, our results provide a novel molecular perspective on the unique properties of the insula and claustrum.

Do the Dento-Thalamic Connections of Genetic Absence Epilepsy Rats from Strasbourg Differ from Those of Control Wistar Rats?

The thalamo-cortical circuit is important in the genesis of absence epilepsy. This circuit can be influenced by connecting pathways from various parts of central nervous system. The aim of the present study is to define the dento-thalamic connections in Wistar animals and compare the results with genetic absence epilepsy rats from Strasbourg (GAERS) using the biotinylated dextran amine (BDA) tracer. We injected BDA into the dentate nucleus of 13 (n = 6 Wistar and n = 7 GAERS) animals. The dento-thalamic connections in the Wistar animals were denser and were connected to a wider range of thalamic nuclei compared with GAERS. The dentate nucleus was bilaterally connected to the central (central medial [CM], paracentral [PC]), ventral (ventral medial [VM], ventral lateral [VL], and ventral posterior lateral [VPL]), and posterior (Po) thalamic nuclei in Wistar animals. The majority of these connections were dense contralaterally and scarce ipsilaterally. Contralateral connections were present with the parafascicular (PF), ventral posterior medial, ventral anterior (VA), and central lateral (CL) thalamic nuclei in Wistar animals. Whereas in GAERS, bilateral connections were observed with the VL and CM. Contralateral connections were present with the PC, VM, VA, and PF thalamic nuclei in GAERS. The CL, VPL, and Po thalamic nucleus connections were not observed in GAERS. The present study showed weak/deficit dento-thalamic connections in GAERS compared with control Wistar animals. The scarce information flow from the dentate nucleus to thalamus in GAERS may have a deficient modulatory role on the thalamus and thus may affect modulation of the thalamo-cortical circuit.

Reproductive toxic effects and possible mechanisms of zonisamide in male rats

Zonisamide (ZNS) is an anticonvulsant which is used to treat the symptoms of epilepsy. Although it is frequently used during reproductive ages, studies that investigated the effects of ZNS on reproductive system are limited. Therefore, we aimed to assess the effects of ZNS on male reproductive system by oral administration to rats in 25, 50, and 100 mg/kg doses for 28 days. After the exposure period, sperm concentration, motility, morphology, and DNA damage, as biomarkers of reproductive toxic effects, were determined, and histopathological examination of testis was performed. In addition, levels of the hormones that play a role in the regulation of reproductive functions, such as follicle-stimulating hormone, luteinizing hormone (LH), and testosterone were measured and the levels of oxidative stress biomarkers that take part in the reproductive pathologies such as catalase, superoxide dismutase, glutathione, and malondialdehyde, were determined. Reproductive toxic effects related to ZNS administration were shown by the significant decrease of sperm concentration and normal sperm morphology in ZNS groups. Additionally, pathological findings were observed in the testicular tissues of ZNS-administered groups dose dependently. In addition, serum LH and testosterone levels were significantly decreased in the ZNS groups. Decreased catalase activities and increased malondialdehyde levels in ZNS groups were evaluated as oxidative stress findings in the testis tissue. It could be expressed that ZNS administration induced dose-dependent reproductive toxic effects in rats, and pathological findings associated with the reproductive system could be the result of that hormonal changes and testicular oxidative stress, which in turn might be considered as possible mechanisms of male reproductive toxicity.

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.

Altered temporal dynamics of brain activity in patients with generalized tonic-clonic seizures

Generalized seizures engage bilateral networks from their onset at a low temporal scale. Previous studies findings have demonstrated focal/local brain activity abnormalities in the patients with generalized tonic-clonic seizures (GTCS). Resting state functional magnetic resonance imaging (fMRI) allows the detection of aberrant spontaneous brain activity in GTCS. Little is known, however, about alterations of dynamics (temporal variability) of spontaneous brain activity. It also remains unclear whether temporal variability of spontaneous brain activity is associated with disease severity. To address these questions, the current study assessed patients with GTCS (n = 35), and age- and sex-matched healthy controls (HCs, n = 33) who underwent resting state fMRI. We first assessed the dynamics of spontaneous brain activity using dynamic amplitude of low-frequency fluctuation (dALFF). Furthermore, the temporal variability of brain activity was quantified as the variance of dALFF across sliding window. Compared to HCs, patients with GTCS showed hyper-temporal variability of dALFF in parts of the default mode network, whereas they showed hypo-temporal variability in the somatomotor cortex. Furthermore, dynamic ALFF in the subgenual anterior cingulate cortex was positively correlated with duration of disease, indicating that disease severity is associated with excessive variability. These results suggest both an excessive variability and excessive stability in patients with GTCS. Overall, the current findings from brain activity dynamics contribute to our understanding of the pathophysiological mechanisms of generalized seizure.

Characterizing Brain Connectivity From Human Electrocorticography Recordings With Unobserved Inputs During Epileptic Seizures

Epilepsy is a neurological disorder characterized by the sudden occurrence of unprovoked seizures. There is extensive evidence of significantly altered brain connectivity during seizure periods in the human brain. Research on analyzing human brain functional connectivity during epileptic seizures has been limited predominantly to the use of the correlation method. However, spurious connectivity can be measured between two brain regions without having direct connection or interaction between them. Correlations can be due to the apparent interactions of the two brain regions resulting from common input from a third region, which may or may not be observed. Hence, researchers have recently proposed a sparse-plus-latent-regularized precision matrix (SLRPM) when there are unobserved or latent regions interacting with the observed regions. The SLRPM method yields partial correlations of the conditional statistics of the observed regions given the latent regions, thus identifying observed regions that are conditionally independent of both the observed and latent regions. We evaluate the performance of the methods using a spring-mass artificial network and assuming that some nodes cannot be observed, thus constituting the latent variables in the example. Several cases have been considered, including both sparse and dense connections, short-range and long-range connections, and a varying number of latent variables. The SLRPM method is then applied to estimate brain connectivity during epileptic seizures from human ECoG recordings. Seventy-four clinical seizures from five patients, all having complex partial epilepsy, were analyzed using SLRPM, and brain connectivity was quantified using modularity index, clustering coefficient, and eigenvector centrality. Furthermore, using a measure of latent inputs estimated by the SLRPM method, it was possible to automatically detect 72 of the 74 seizures with four false positives and find six seizures that were not marked manually.

Relationship Between Seizure Frequency and Functional Abnormalities in Limbic Network of Medial Temporal Lobe Epilepsy

Background: We compared resting-state functional connectivity (RSFC) among limbic and temporal lobe regions between patients with medial temporal lobe epilepsy (mTLE) and healthy control subjects to identify imaging evidence of functional networks related to seizure frequency, age of seizure onset, and duration of epilepsy.

Methods: Twelve patients with drug-resistant, unilateral medial temporal lobe epilepsy and 12 healthy control subjects matched for age, sex, and handedness participated in the imaging experiments. We used network-based statistics to compare functional connectivity graphs in patients with mTLE and healthy controls to investigate the relationship between functional connectivity abnormalities and seizure frequency.

Results: Among mTLE patients, we found functional network abnormalities throughout the limbic system, but primarily in the hemisphere ipsilateral to the seizure focus. The RSFCs between ipsilateral hypothalamus and ventral anterior cingulate cortex and between ipsilateral subiculum and contralateral posterior cingulate cortex were highly correlated with seizure frequency.

Discussion: These findings suggest that in mTLE, changes in limbic networks ipsilateral to the epileptic focus are common. The pathological changes in connectivity between cingulate cortex, hypothalamus and subiculum ipsilateral to the seizure focus were correlated with increased seizure frequency.

Absence of an Autonomic Sign Assists in the Diagnosis of Extratemporal Lobe Epilepsy Manifesting Generalized Convulsion with Retained Awareness

We herein report two epilepsy patients with the seizure focus in the non-dominant hemisphere manifesting secondarily generalized convulsion (sGC) with retained awareness characterized by a lack of autonomic signs although GC was complicated by respiratory arrest. Given the semiology and electrophysiological findings, the seizure activity was considered to propagate to the supplementary-motor area and the bilateral primary-motor area, with a clinical manifestation of sGC. The absence of autonomic signs during GC can be a key indicator that the seizure remains in the bilateral suprasylvian area and thus does not involve the region necessary for awareness preservation, which may assist in the diagnosis of this atypical epileptic seizure.

Spontaneous Recurrent Absence Seizure-like Events in Wild-Caught Rats

Absence epilepsy is a heritable human neurological disorder characterized by brief nonconvulsive seizures with behavioral arrest, moderate-to-severe loss of consciousness (absence), and distinct spike-wave discharges (SWDs) in the EEG and electrocorticogram (ECoG). Genetic models of this disorder have been created by selectively inbreeding rats for absence seizure-like events with similar electrical and behavioral characteristics. However, these events are also common in outbred laboratory rats, raising concerns about whether SWD/immobility accurately reflects absence epilepsy as opposed to "normal" rodent behavior. We hypothesized that, if SWD/immobility models absence seizures, it would not exist in wild-caught rats due to the pressures of natural selection. To test this hypothesis, we compared chronic video/electrocorticogram recordings from male and female wild-caught (Brown-Norway [BN]) rats to recordings from laboratory outbred BN, outbred Long-Evans, and inbred WAG/Rij rats (i.e., a model of absence epilepsy). Wild-caught BN rats displayed absence-like SWD/immobility events that were highly similar to outbred BN rats in terms of spike-wave morphology, frequency, diurnal rhythmicity, associated immobility, and sensitivity to the anti-absence drug, ethosuximide; however, SWD bursts were less frequent and of shorter duration in wild-caught and outbred BN rats than the outbred Long-Evans and inbred WAG/Rij strains. We conclude that SWD/immobility in rats does not represent absence seizures, although they appear to have many similarities. In wild rats, SWD/immobility appears to represent normal brain activity that does not reduce survival in natural environments, a conclusion that logically extends to outbred laboratory rats and possibly to those that have been inbred to model absence epilepsy.SIGNIFICANCE STATEMENT Spike-wave discharges (SWDs), behavioral arrest, and diminished consciousness are cardinal signs of seizures in human absence epilepsy and are used to model this disorder in inbred rats. These characteristics, however, are routinely found in outbred laboratory rats, leading to debate on whether SWD/immobility is a valid model of absence seizures. The SWD/immobility events in wild-caught rats appear equivalent to those found in outbred and inbred rat strains, except for lower incidence and shorter durations. Our results indicate that the electrophysiological and behavioral characteristics of events underlying hypothetical absence epilepsy in rodent models are found in wild rats captured in their natural environment. Other criteria beyond observation of SWDs and associated immobility are required to objectively establish absence epilepsy in rat models.

BOLD-fMRI activity informed by network variation of scalp EEG in juvenile myoclonic epilepsy

Epilepsy is marked by hypersynchronous bursts of neuronal activity, and seizures can propagate variably to any and all areas, leading to brain network dynamic organization. However, the relationship between the network characteristics of scalp EEG and blood oxygenation level-dependent (BOLD) responses in epilepsy patients is still not well known. In this study, simultaneous EEG and fMRI data were acquired in 18 juvenile myoclonic epilepsy (JME) patients. Then, the adapted directed transfer function (ADTF) values between EEG electrodes were calculated to define the time-varying network. The variation of network information flow within sliding windows was used as a temporal regressor in fMRI analysis to predict the BOLD response. To investigate the EEG-dependent functional coupling among the responding regions, modulatory interactions were analyzed for network variation of scalp EEG and BOLD time courses. The results showed that BOLD activations associated with high network variation were mainly located in the thalamus, cerebellum, precuneus, inferior temporal lobe and sensorimotor-related areas, including the middle cingulate cortex (MCC), supplemental motor area (SMA), and paracentral lobule. BOLD deactivations associated with medium network variation were found in the frontal, parietal, and occipital areas. In addition, modulatory interaction analysis demonstrated predominantly directional negative modulation effects among the thalamus, cerebellum, frontal and sensorimotor-related areas. This study described a novel method to link BOLD response with simultaneous functional network organization of scalp EEG. These findings suggested the validity of predicting epileptic activity using functional connectivity variation between electrodes. The functional coupling among the thalamus, frontal regions, cerebellum and sensorimotor-related regions may be characteristically involved in epilepsy generation and propagation, which provides new insight into the pathophysiological mechanisms and intervene targets for JME.

The Claustrum in Relation to Seizures and Electrical Stimulation

The neural mechanisms of altered consciousness that accompanies most epileptic seizures are not known. We have reported alteration of consciousness resulting from electrical stimulation of the claustrum via a depth electrode in a woman with refractory focal epilepsy. Additionally, there are reports that suggest possible claustral involvement in focal epilepsy, including MRI findings of bilaterally increased T2 signal intensity in patients with status epilepticus (SE). Although its cytoarchitecture and connectivity have been studied extensively, the precise role of the claustrum in consciousness processing, and, thus, its contribution to the semiology of dyscognitive seizures are still elusive. To investigate the role of the claustrum in rats, we studied the effect of high-frequency stimulation (HFS) of the claustrum on performance in the operant chamber. We also studied the inter-claustral and the claustro-hippocampal connectivity through cerebro-cerebral evoked potentials (CCEPs), and investigated the involvement of the claustrum in kainate (KA)-induced seizures. We found that HFS of the claustrum decreased the performance in the operant task in a manner that was proportional to the current intensity used. In this article, we present previously unpublished data about the effect of stimulating extra-claustral regions in the operant chamber task as a control experiment. In these animals, stimulation of the corpus callosum, the largest interhemispheric commissure, as well as the orbitofrontal cortex in the vicinity of the claustrum did not produce that same effect as with claustral stimulation. Additionally, CCEPs established the presence of effective connectivity between both claustra, as well as between the claustrum and bilateral hippocampi indicating that these connections may be part of the circuitry involved in alteration of consciousness in limbic seizures. Lastly, some seizures induced by KA injections showed an early involvement of the claustrum with later propagation to the hippocampi. Further work is needed to clarify the exact role of the claustrum in mediating alteration of consciousness during epileptic seizures.

Alterations in Brain Metabolites in Patients with Epilepsy with Impaired Consciousness: A Case-Control Study of Interictal Multivoxel 1H-MRS Findings

BACKGROUND AND PURPOSE

Previous studies have shown perfusion abnormalities in the thalamus and upper brain stem in patients with epilepsy with impaired consciousness. We hypothesized that these areas associated with consciousness will also show metabolic abnormalities. However, metabolic abnormalities in those areas correlated with consciousness has not been characterized with multiple-voxel ¹H-MRS. In this study, we investigated the metabolic alterations in these brain regions and assessed the correlation between seizure features and metabolic alterations.

MATERIALS AND METHODS

Fifty-seven patients with epilepsy and 24 control subjects underwent routine MR imaging and 3D multiple-voxel ¹H-MRS. Patients were divided into 3 subgroups: focal impaired awareness seizures (n = 18), primary generalized tonic-clonic seizures (n = 19), and secondary generalized tonic-clonic seizures (n = 20). The measured metabolite alterations in NAA/Cr, NAA/(Cr + Cho), and Cho/Cr ratios in brain regions associated with the consciousness network were compared between the patient and control groups. ROIs were placed in the bilateral inferior frontal gyrus, supramarginal gyrus, cingulate gyrus, precuneus, thalamus, and upper brain stem. Correlations between clinical parameters (epilepsy duration and seizure frequency) and metabolite alterations were analyzed.

RESULTS

Significantly lower NAA/Cr and NAA/(Cho + Cr) ratios (P < .05 and < .01, respectively) were observed in the bilateral thalamus and upper brain stem in all experimental groups, and significantly high Cho/Cr ratios (P < .05) were observed in the right thalamus in the focal impaired awareness seizures group. There were no significant differences in metabolite ratios among the 3 patient groups (P > .05). The secondary generalized tonic-clonic seizures group showed a negative correlation between the duration of epilepsy and the NAA/(Cr + Cho) ratio in the bilateral thalamus (P < .05).

CONCLUSIONS

Metabolic alterations were observed in the brain stem and thalamus in patients with epilepsy with impaired consciousness.

Conflicting emergences. Weak vs. strong emergence for the modelling of brain function

The concept of "emergence" has become commonplace in the modelling of complex systems, both natural and man-made; a functional property" emerges" from a system when it cannot be readily explained by the properties of the system's sub-units. A bewildering array of adaptive and sophisticated behaviours can be observed from large ensembles of elementary agents such as ant colonies, bird flocks or by the interactions of elementary material units such as molecules or weather elements. Ultimately, emergence has been adopted as the ontological support of a number of attempts to model brain function. This manuscript aims to clarify the ontology of emergence and delve into its many facets, particularly into its "strong" and "weak" versions that underpin two different approaches to the modelling of behaviour. The first group of models is here represented by the "free energy" principle of brain function and the "integrated information theory" of consciousness. The second group is instead represented by computational models such as oscillatory networks that use mathematical scalable representations to generate emergent behaviours and are then able to bridge neurobiology with higher mental functions. Drawing on the epistemological literature, we observe that due to their loose mechanistic links with the underlying biology, models based on strong forms of emergence are at risk of metaphysical implausibility. This, in practical terms, translates into the over determination that occurs when the proposed model becomes only one of a large set of possible explanations for the observable phenomena. On the other hand, computational models that start from biologically plausible elementary units, hence are weakly emergent, are not limited by ontological faults and, if scalable and able to realistically simulate the hierarchies of brain output, represent a powerful vehicle for future neuroscientific research programmes.

Transition of brain networks from an interictal to a preictal state preceding a seizure revealed by scalp EEG network analysis

Epilepsy is a neurological disorder in the brain that is characterized by unprovoked seizures. Epileptic seizures are attributed to abnormal synchronous neuronal activity in the brain. To detect the seizure as early as possible, the identification of specific electroencephalogram (EEG) dynamics is of great importance in investigating the transition of brain activity as the epileptic seizure approaches. In this study, we investigated the transition of brain activity from interictal to preictal states preceding a seizure by combining EEG network and clustering analyses together in different frequency bands. The findings of this study demonstrated the best clustering performance of k-medoids in the beta band; in addition, compared to the interictal state, the preictal state experienced increased synchronization of EEG network connectivity, characterized by relatively higher network properties. These findings can provide helpful insight into the mechanism of epilepsy, which can also be used in the prediction of epileptic seizures and subsequent intervention.

Mechanisms of decreased cholinergic arousal in focal seizures: In vivo whole-cell recordings from the pedunculopontine tegmental nucleus

Focal limbic seizures often impair consciousness/awareness with major negative impact on quality of life. Recent work has shown that limbic seizures depress brainstem arousal systems, including reduced action potential firing in a key node: cholinergic neurons of the pedunculopontine tegmental nucleus (PPT). In vivo whole-cell recordings have not previously been achieved in PPT, but are used here with the goal of elucidating the mechanisms of reduced PPT cholinergic neuronal activity. An established model of focal limbic seizures was used in rats following brief hippocampal stimulation under light anesthesia. Whole-cell in vivo recordings were obtained from PPT neurons using custom-fabricated 9-10 mm tapered patch pipettes, and cholinergic neurons were identified histologically. Average membrane potential, input resistance, membrane potential fluctuations and variance were analyzed during seizures. A subset of PPT neurons exhibited reduced firing and hyperpolarization during seizures and stained positive for choline acetyltransferase. These PPT neurons showed a mean membrane potential hyperpolarization of -3.82 mV (±0.81 SEM, P < .05) during seizures, and also showed significantly increased input resistance, fewer excitatory post-synaptic potential (EPSP)-like events (P < .05), and reduced membrane potential variance (P < .01). The combination of increased input resistance, decreased EPSP-like events and decreased variance weigh against active ictal inhibition and support withdrawal of excitatory input as the dominant mechanism of decreased activity of cholinergic neurons in the PPT. Further identifying synaptic mechanisms of depressed arousal during seizures may lead to new treatments to improve ictal and postictal cognition.

Expanding Brain-Computer Interfaces for Controlling Epilepsy Networks: Novel Thalamic Responsive Neurostimulation in Refractory Epilepsy

Seizures have traditionally been considered hypersynchronous excitatory events and epilepsy has been separated into focal and generalized epilepsy based largely on the spatial distribution of brain regions involved at seizure onset. Epilepsy, however, is increasingly recognized as a complex network disorder that may be distributed and dynamic. Responsive neurostimulation (RNS) is a recent technology that utilizes intracranial electroencephalography (EEG) to detect seizures and delivers stimulation to cortical and subcortical brain structures for seizure control. RNS has particular significance in the clinical treatment of medically refractory epilepsy and brain–computer interfaces in epilepsy. Closed loop RNS represents an important step forward to understand and target nodes in the seizure network. The thalamus is a central network node within several functional networks and regulates input to the cortex; clinically, several thalamic nuclei are safe and feasible targets. We highlight the network theory of epilepsy, potential targets for neuromodulation in epilepsy and the first reported use of RNS as a first generation brain–computer interface to detect and stimulate the centromedian intralaminar thalamic nucleus in a patient with bilateral cortical onset of seizures. We propose that advances in network analysis and neuromodulatory techniques using brain–computer interfaces will significantly improve outcomes in patients with epilepsy. There are numerous avenues of future direction in brain–computer interface devices including multi-modal sensors, flexible electrode arrays, multi-site targeting, and wireless communication.

Measuring the Complexity of Consciousness

The grand quest for a scientific understanding of consciousness has given rise to many new theoretical and empirical paradigms for investigating the phenomenology of consciousness as well as clinical disorders associated to it. A major challenge in this field is to formalize computational measures that can reliably quantify global brain states from data. In particular, information-theoretic complexity measures such as integrated information have been proposed as measures of conscious awareness. This suggests a new framework to quantitatively classify states of consciousness. However, it has proven increasingly difficult to apply these complexity measures to realistic brain networks. In part, this is due to high computational costs incurred when implementing these measures on realistically large network dimensions. Nonetheless, complexity measures for quantifying states of consciousness are important for assisting clinical diagnosis and therapy. This article is meant to serve as a lookup table of measures of consciousness, with particular emphasis on clinical applicability. We consider both, principle-based complexity measures as well as empirical measures tested on patients. We address challenges facing these measures with regard to realistic brain networks, and where necessary, suggest possible resolutions.

Whole-brain MEG connectivity-based analyses reveals critical hubs in childhood absence epilepsy

Absence seizures are thought to be linked to abnormal interplays between regions of a thalamocortical network. However, the complexity of this widespread network makes characterizing the functional interactions among various brain regions challenging. Using whole-brain functional connectivity and network analysis of magnetoencephalography (MEG) data, we explored pre-treatment brain hubs ("highly connected nodes") of patients aged 6 to 12 years with childhood absence epilepsy. We analyzed ictal MEG data of 74 seizures from 16 patients. We employed a time-domain beamformer technique to estimate MEG sources in broadband (1-40 Hz) where the greatest power changes between ictal and preictal periods were identified. A phase synchrony measure, phase locking value, and a graph theory metric, eigenvector centrality (EVC), were utilized to quantify voxel-level connectivity and network hubs of ictal > preictal periods, respectively. A volumetric atlas containing 116 regions of interests (ROIs) was utilized to summarize the network measures. ROIs with EVC (z-score) > 1.96 were reported as critical hubs. ROIs analysis revealed functional-anatomical hubs in a widespread network containing bilateral precuneus (right/left, z = 2.39, 2.18), left thalamus (z = 2.28), and three anterior cerebellar subunits of lobule "IV-V" (z = 3.9), vermis "IV-V" (z = 3.57), and lobule "III" (z = 2.03). Findings suggest that highly connected brain areas or hubs are present in focal cortical, subcortical, and cerebellar regions during absence seizures. Hubs in thalami, precuneus and cingulate cortex generally support a theory of rapidly engaging and bilaterally distributed networks of cortical and subcortical regions responsible for seizures generation, whereas hubs in anterior cerebellar regions may be linked to terminating motor automatisms frequently seen during typical absence seizures. Whole-brain network connectivity is a powerful analytic tool to reveal focal components of absence seizures in MEG. Our investigations can lead to a better understanding of the pathophysiology of CAE.

Seizure detection: do current devices work? And when can they be useful?

PURPOSE OF REVIEW

The unpredictability and apparent randomness of epileptic seizures is one of the most vexing aspects of epilepsy. Methods or devices capable of detecting seizures may help prevent injury or even death and significantly improve quality of life. Here, we summarize and evaluate currently available, unimodal, or polymodal detection systems for epileptic seizures, mainly in the ambulatory setting.

RECENT FINDINGS

There are two broad categories of detection devices: EEG-based and non-EEG-based systems. Wireless wearable EEG devices are now available both in research and commercial arenas. Neuro-stimulation devices are currently evolving and initial experiences of these show potential promise. As for non-EEG devices, different detecting systems show different sensitivity according to the different patient and seizure types. Regardless, when used in combination, these modalities may complement each other to increase positive predictive value. Although some devices with high sensitivity are promising, practical widespread use of such detection systems is still some way away. More research and experience are needed to evaluate the most efficient and integrated systems, to allow for better approaches to detection and prediction of seizures. The concept of closed-loop systems and prompt intervention may substantially improve quality of life for patients and carers.

Epilepsy

Epilepsy affects all age groups and is one of the most common and most disabling neurological disorders. The accurate diagnosis of seizures is essential as some patients will be misdiagnosed with epilepsy, whereas others will receive an incorrect diagnosis. Indeed, errors in diagnosis are common, and many patients fail to receive the correct treatment, which often has severe consequences. Although many patients have seizure control using a single medication, others require multiple medications, resective surgery, neuromodulation devices or dietary therapies. In addition, one-third of patients will continue to have uncontrolled seizures. Epilepsy can substantially impair quality of life owing to seizures, comorbid mood and psychiatric disorders, cognitive deficits and adverse effects of medications. In addition, seizures can be fatal owing to direct effects on autonomic and arousal functions or owing to indirect effects such as drowning and other accidents. Deciphering the pathophysiology of epilepsy has advanced the understanding of the cellular and molecular events initiated by pathogenetic insults that transform normal circuits into epileptic circuits (epileptogenesis) and the mechanisms that generate seizures (ictogenesis). The discovery of >500 genes associated with epilepsy has led to new animal models, more precise diagnoses and, in some cases, targeted therapies.

Seizure activity and individual vulnerability on first-episode interictal psychosis in epilepsy

OBJECTIVE

Despite a theoretical consensus that interictal psychosis (IIP) is related to various epilepsy-related factors, the impact of seizure activity on development of IIP remains inconclusive. This is the first controlled study using quantitative seizure-activity measures at the onset of IIP.

METHODS

One hundred and eighty-one patients with epilepsy who exhibited first-episode IIP (IIP group) and 427 patients with epilepsy without psychotic episodes (control group) were enrolled. The control group was matched for age, epilepsy type, and duration of epilepsy. The two seizure-activity indices (seizure frequency at the time of onset of first-episode IIP and the number of seizures before the onset of IIP) were evaluated and compared between the IIP and control groups. Logistic regression analysis was used for extracting risk variables to develop first-episode IIP.

RESULTS

The sum of previous seizures was greater in the IIP than in control groups. This was particularly the case in the patients with partial epilepsies (PE). Higher seizure frequency in the patients with PE was associated with the development of first-episode IIP while no association was found in the whole cohort or in the patients with generalized epilepsies (GE). Subsequent multivariate analysis revealed the sum of previous seizures and family history of psychosis as risk variables to first-episode IIP.

CONCLUSIONS

The accumulation of seizure-related damages and family history of psychosis is associated with the onset of IIP episodes, particularly in the patients with PE. Seizure activity and individual vulnerability to psychosis are likely to be interacted for as the development of IIP in patients with epilepsy.

Characterisation of ictal and interictal states of epilepsy: A system dynamic approach of principal dynamic modes analysis

Epilepsy is a brain disorder characterised by the recurrent and unpredictable interruptions of normal brain function, called epileptic seizures. The present study attempts to derive new diagnostic indices which may delineate between ictal and interictal states of epilepsy. To achieve this, the nonlinear modeling approach of global principal dynamic modes (PDMs) is adopted to examine the functional connectivity of the temporal and frontal lobes with the occipital brain segment using an ensemble of paediatric EEGs having the presence of epileptic seizure. The distinct spectral characteristics of global PDMs are found to be in line with the neural rhythms of brain dynamics. Moreover, we find that the linear trends of associated nonlinear functions (ANFs) associated with the 2nd and 4th global PDMs (representing delta, theta and alpha bands) of Fp1–F3 may differentiate between ictal and interictal states of epilepsy. These findings suggest that global PDMs and their associated ANFs may offer potential utility as diagnostic neural measures for ictal and interictal states of epilepsy.

Generalized nonmotor (absence) seizures-What do absence, generalized, and nonmotor mean?

OBJECTIVE

Clinical absences are now classified as "generalized nonmotor (absence) seizures" by the International League Against Epilepsy (ILAE). The aim of this paper is to critically review the concept of absences and to put the accompanying focal and motor symptoms into the context of the emerging pathophysiological knowledge.

METHODS

For this narrative review we performed an extensive literature search on the term "absence," and analyzed the plethora of symptoms observed in clinical absences.

RESULTS

Arising from the localization and the involved cortical networks, motor symptoms may include bilateral mild eyelid fluttering and mild myoclonic jerks of extremities. These motor symptoms may also occur unilaterally, analogous to a focal motor seizure with Jacksonian march. Furthermore, electroencephalography (EEG) abnormalities may exhibit initial frontal focal spikes and consistent asymmetries. Electroclinical characteristics support the cortical focus theory of absence seizures. Simultaneous EEG/functional magnetic resonance imaging (fMRI) measurements document cortical deactivation and thalamic activation. Cortical deactivation is related to slow waves and disturbances of consciousness of varying degrees. Motor symptoms correspond to the spike component of the 3/s spike-and-wave-discharges. Thalamic activation can be interpreted as a response to overcome cortical deactivation. Furthermore, arousal reaction during drowsiness or sleep triggers spikes in an abnormally excitable cortex. An initial disturbance in arousal mechanisms ("dyshormia") might be responsible for the start of this abnormal sequence.

SIGNIFICANCE

The classification as "generalized nonfocal and nonmotor (absence) seizure" does not covey the complex semiology of a patient's clinical events.

A pilot study of the role of the claustrum in attention and seizures in rats

OBJECTIVE

The claustrum has been implicated in consciousness, and MRIs of patients with status epilepticus have shown increased claustral signal intensity. In an attempt to investigate the role of claustrum in cognition and seizures, we (1) assessed the effect of high-frequency stimulation (HFS) of the claustrum on performance in the operant chamber; (2) studied interclaustral and claustrohippocampal connectivity through cerebro-cerebral evoked potentials (CCEPs); and (3) investigated the role of claustrum in kainate-induced (KA) seizures.

METHODS

Adult male Sprague-Dawley rats were trained in operant conditioning and implanted with electrodes in bilateral claustra and hippocampi. Claustrum HFS (50 Hz) was delivered bilaterally and unilaterally with increasing intensities from 50 to 1000 μA, and performance scores were assessed. CCEPs were studied by averaging the responses to bipolar stimulations, 1-ms wide pulses at 0.1 Hz to the claustrum. KA seizures were analyzed on video-EEG recordings.

RESULTS

Generalized Estimating Equations analysis revealed that claustral stimulation reduced task performance scores relative to rest sessions (bilateral: -15.8 percentage points, p < 0.0001; unilateral: -15.2, p < 0.0001). With some stimulations, the rats showed a stimulus-locked decrease in attentiveness and, occasionally, an inability to complete the operant task. CCEPs demonstrated interclaustral and claustrohippocampal connectivity. Some KA seizures appeared to originate from the claustrum.

CONCLUSIONS

Findings from the operant conditioning task suggest stimulation of the claustrum can alter attention or awareness. CCEPs demonstrated connectivity between the two claustra and between the claustrum and the hippocampi. Such connectivity may be part of the circuitry that underlies the alteration of awareness in limbic seizures. Lastly, KA seizures showed early involvement of the claustrum, a finding that also supports a possible role of the claustrum in the alteration of consciousness that accompanies dyscognitive seizures.

The Revised Definition and Classification of Epilepsy for Neurodiagnostic Technologists

The definition of who has epilepsy, classification of seizure types, and types of epilepsy have all recently been revised. The classical definition of epilepsy as a person having two or more unprovoked seizures more than 24 hours apart has been expanded also to include those with one seizure and a high likelihood (more than 60%) of having another. In the new definition, epilepsy is considered to be resolved when a person is seizure-free for 10 years, the terminal 5 being off seizure medicines, or when an age-dependent syndrome has been outgrown. The new seizure type classification revises the 1981 system but maintains the primary distinction of focal- versus generalized-onset seizures. Seizures also can be of unknown onset. Focal seizures may demonstrate retention or impairment of awareness, resulting in focal-aware or focal-impaired awareness seizures. Several new focal and generalized seizure types are introduced. Classification of the epilepsies is now by grouping of seizure types, etiologies, comorbidities, and epilepsy syndromes. The goal of the new terminology is greater clarity of communication and more accurate grouping of seizure types for research. Neurodiagnostic technologists can be of great help in observing clinical and electrographic features that will define the type of seizure.

The different patterns of seizure-induced aphasia in temporal lobe epilepsies

OBJECTIVES

Ictal language disturbances may occur in dominant hemisphere temporal lobe epilepsy (TLE), but little is known about the precise anatomoelectroclinical correlations. This study investigated the different facets of ictal aphasia in intracerebrally recorded TLE.

METHODS

Video-stereoelectroencephalography (SEEG) recordings of 37 seizures in 17 right-handed patients with drug-resistant TLE were analyzed; SEEG electroclinical correlations between language disturbance and involvement of temporal lobe structures were assessed. In the clinical analysis, we separated speech disturbance from loss of consciousness.

RESULTS

According to the region involved, different patterns of ictal aphasia in TLE were identified. Impaired speech comprehension was associated with posterior lateral involvement, anomia and reduced verbal fluency with anterior mediobasal structures, and jargonaphasia with basal temporal involvement. The language production deficits, such as anomia and low fluency, cannot be simply explained by an involvement of Broca's area, since this region was not affected by seizure discharge.

SIGNIFICANCE

Assessment of language function in the early ictal state can be successfully performed and provides valuable information on seizure localization within the temporal lobe as well as potentially useful information for guiding surgery.

Cognitive and Neurophysiological Recovery Following Electroconvulsive Therapy: A Study Protocol

Electroconvulsive therapy (ECT) employs the elective induction of generalizes seizures as a potent treatment for severe psychiatric illness. As such, ECT provides an opportunity to rigorously study the recovery of consciousness, reconstitution of cognition, and electroencephalographic (EEG) activity following seizures. Fifteen patients with major depressive disorder refractory to pharmacologic therapy will be enrolled (Clinicaltrials.gov, NCT02761330). Adequate seizure duration will be confirmed following right unilateral ECT under etomidate anesthesia. Patients will then undergo randomization for the order in which they will receive three sequential treatments: etomidate + ECT, ketamine + ECT, and ketamine + sham ECT. Sessions will be repeated in the same sequence for a total of six treatments. Before each session, sensorimotor speed, working memory, and executive function will be assessed through a standardized cognitive test battery. After each treatment, the return of purposeful responsiveness to verbal command will be determined. At this point, serial cognitive assessments will begin using the same standardized test battery. The presence of delirium and changes in depression severity will also be ascertained. Sixty-four channel EEG will be acquired throughout baseline, ictal, and postictal epochs. Mixed-effects models will correlate the trajectories of cognitive recovery, clinical outcomes, and EEG metrics over time. This innovative research design will answer whether: (1) time to return of responsiveness will be prolonged with ketamine + ECT compared with ketamine + sham ECT; (2) time of restoration to baseline function in each cognitive domain will take longer after ketamine + ECT than after ketamine + sham ECT; (3) postictal delirium is associated with delayed restoration of baseline function in all cognitive domains; and (4) the sequence of reconstitution of cognitive domains following the three treatments in this study is similar to that occurring after an isoflurane general anesthetic (NCT01911195). Sub-studies will assess the relationships of cognitive recovery to the EEG preceding, concurrent, and following individual ECT sessions. Overall, this study will lead the development of biomarkers for tailoring the cogno-affective recovery of patients undergoing ECT.

Seizures and Sleep in the Thalamus: Focal Limbic Seizures Show Divergent Activity Patterns in Different Thalamic Nuclei

The thalamus plays diverse roles in cortical-subcortical brain activity patterns. Recent work suggests that focal temporal lobe seizures depress subcortical arousal systems and convert cortical activity into a pattern resembling slow-wave sleep. The potential simultaneous and paradoxical role of the thalamus in both limbic seizure propagation, and in sleep-like cortical rhythms has not been investigated. We recorded neuronal activity from the central lateral (CL), anterior (ANT), and ventral posteromedial (VPM) nuclei of the thalamus in an established female rat model of focal limbic seizures. We found that population firing of neurons in CL decreased during seizures while the cortex exhibited slow waves. In contrast, ANT showed a trend toward increased neuronal firing compatible with polyspike seizure discharges seen in the hippocampus. Meanwhile, VPM exhibited a remarkable increase in sleep spindles during focal seizures. Single-unit juxtacellular recordings from CL demonstrated reduced overall firing rates, but a switch in firing pattern from single spikes to burst firing during seizures. These findings suggest that different thalamic nuclei play very different roles in focal limbic seizures. While limbic nuclei, such as ANT, appear to participate directly in seizure propagation, arousal nuclei, such as CL, may contribute to depressed cortical function, whereas sleep spindles in relay nuclei, such as VPM, may interrupt thalamocortical information flow. These combined effects could be critical for controlling both seizure severity and impairment of consciousness. Further understanding of differential effects of seizures on different thalamocortical networks may lead to improved treatments directly targeting these modes of impaired function.SIGNIFICANCE STATEMENT Temporal lobe epilepsy has a major negative impact on quality of life. Previous work suggests that the thalamus plays a critical role in thalamocortical network modulation and subcortical arousal maintenance, but its precise seizure-associated functions are not known. We recorded neuronal activity in three different thalamic regions and found divergent activity patterns, which may respectively participate in seizure propagation, impaired level of conscious arousal, and altered relay of information to the cortex during focal limbic seizures. These very different activity patterns within the thalamus may help explain why focal temporal lobe seizures often disrupt widespread network function, and can help guide future treatments aimed at restoring normal thalamocortical network activity and cognition.

The Thymus/Neocortex Hypothesis of the Brain: A Cell Basis for Recognition and Instruction of Self

The recognition of internal and external sources of stimuli, the self from non-self, seems to be an intrinsic property to the adequate functioning of the immune system and the nervous system, both complex network systems that have evolved to safeguard the self biological identity of the organism. The mammalian brain development relies on dynamic and adaptive processes that are now well described. However, the rules dictating this highly constrained developmental process remain elusive. Here we hypothesize that there is a cellular basis for brain selfhood, based on the analogy of the global mechanisms that drive the self/non-self recognition and instruction by the immune system. In utero education within the thymus by multi-step selection processes discard overly low and high affinity T-lymphocytes to self stimuli, thus avoiding expendable or autoreactive responses that might lead to harmful autoimmunity. We argue that the self principle is one of the chief determinants of neocortical brain neurogenesis. According to our hypothesis, early-life education on self at the subcortical plate of the neocortex by selection processes might participate in the striking specificity of neuronal repertoire and assure efficiency and self tolerance. Potential implications of this hypothesis in self-reactive neurological pathologies are discussed, particularly involving consciousness-associated pathophysiological conditions, i.e., epilepsy and schizophrenia, for which we coined the term autophrenity.

Multifaceted brain networks reconfiguration in disorders of consciousness uncovered by co-activation patterns

INTRODUCTION

Given that recent research has shown that functional connectivity is not a static phenomenon, we aim to investigate the dynamic properties of the default mode network's (DMN) connectivity in patients with disorders of consciousness.

METHODS

Resting-state fMRI volumes of a convenience sample of 17 patients in unresponsive wakefulness syndrome (UWS) and controls were reduced to a spatiotemporal point process by selecting critical time points in the posterior cingulate cortex (PCC). Spatial clustering was performed on the extracted PCC time frames to obtain 8 different co-activation patterns (CAPs). We investigated spatial connectivity patterns positively and negatively correlated with PCC using both CAPs and standard stationary method. We calculated CAPs occurrences and the total number of frames.

RESULTS

Compared to controls, patients showed (i) decreased within-network positive correlations and between-network negative correlations, (ii) emergence of "pathological" within-network negative correlations and between-network positive correlations (better defined with CAPs), and (iii) "pathological" increases in within-network positive correlations and between-network negative correlations (only detectable using CAPs). Patients showed decreased occurrence of DMN-like CAPs (1-2) compared to controls. No between-group differences were observed in the total number of frames CONCLUSION: CAPs reveal at a more fine-grained level the multifaceted spatial connectivity reconfiguration following the DMN disruption in UWS patients, which is more complex than previously thought and suggests alternative anatomical substrates for consciousness. BOLD fluctuations do not seem to differ between patients and controls, suggesting that BOLD response represents an intrinsic feature of the signal, and therefore that spatial configuration is more important for consciousness than BOLD activation itself. Hum Brain Mapp 39:89-103, 2018. © 2017 Wiley Periodicals, Inc.

Impairment of consciousness induced by bilateral electrical stimulation of the frontal convexity

We report a case of impairment of consciousness (IOC) induced by electrical cortical stimulation (ECS) of homologous regions within the lateral frontal convexities in a patient with medically intractable epilepsy. The patient had mixed features of idiopathic generalized and focal epilepsy. On intracranial EEG recording, interictal and ictal discharges showed a high degree of synchrony across widespread bilateral fronto-parietal areas. We identified regions in the lateral frontal lobes that reliably and produced loss of consciousness by ECS. This was accompanied by evoked EEG activity of admixed frequencies over the fronto-parietal, mesial frontal and temporal regions during stimulation and was not associated with after-discharges. Symptoms were immediately reversible upon cessation of stimulation. This finding suggests that focal cortical stimulation can disrupt widespread networks that underlie consciousness. Individuals with high degrees of speculated thalamo-frontal cortical connectivity might be more susceptible to this effect, and the findings highlight the importance of standardizing the testing of level of consciousness during mapping sessions.

Although consciousness is commonly impaired in epileptic seizures, limited literature is available on loss of consciousness induced by electrical cortical stimulation (ECS) in humans undergoing intracranial EEG evaluations for localization of epileptic focus. One theory advocates the presence of consciousness ‘switch’ in subcortical structures. While this model is novel and simplistic, it has its inherent limitations. In this case study, we propose an alternative approach on the entity and discuss the complex circuits underlying it and correlate that with the electrophysiological findings and the pathophysiology of the phenotype of the disease and discuss potential causes for rarity of reports on the subject.

Time-Varying Networks of Inter-Ictal Discharging Reveal Epileptogenic Zone

The neuronal synchronous discharging may cause an epileptic seizure. Currently, most of the studies conducted to investigate the mechanism of epilepsy are based on EEGs or functional magnetic resonance imaging (fMRI) recorded during the ictal discharging or the resting-state, and few studies have probed into the dynamic patterns during the inter-ictal discharging that are much easier to record in clinical applications. Here, we propose a time-varying network analysis based on adaptive directed transfer function to uncover the dynamic brain network patterns during the inter-ictal discharging. In addition, an algorithm based on the time-varying outflow of information derived from the network analysis is developed to detect the epileptogenic zone. The analysis performed revealed the time-varying network patterns during different stages of inter-ictal discharging; the epileptogenic zone was activated prior to the discharge onset then worked as the source to propagate the activity to other brain regions. Consistence between the epileptogenic zones detected by our proposed approach and the actual epileptogenic zones proved that time-varying network analysis could not only reveal the underlying neural mechanism of epilepsy, but also function as a useful tool in detecting the epileptogenic zone based on the EEGs in the inter-ictal discharging.

Voluntary Control of Epileptiform Spike-Wave Discharges in Awake Rats

Genetically inherited absence epilepsy in humans is typically characterized by brief (seconds) spontaneous seizures, which involve spike-wave discharges (SWDs) in the EEG and interruption of consciousness and ongoing behavior. Genetic (inbred) models of this disorder in rats have been used to examine mechanisms, comorbidities, and antiabsence drugs. SWDs have also been proposed as models of complex partial seizures (CPSs) following traumatic brain injury (post-traumatic epilepsy). However, the ictal characteristics of these rat models, including SWDs and associated immobility, are also prevalent in healthy outbred laboratory rats. We therefore hypothesized that SWDs are not always associated with classically defined absence seizures or CPSs. To test this hypothesis, we used operant conditioning in male rats to determine whether outbred strains, Sprague Dawley and Long-Evans, and/or the inbred WAG/Rij strain (a rat model of heritable human absence epilepsy) could exercise voluntary control over these epileptiform events. We discovered that both inbred and outbred rats could shorten the duration of SWDs to obtain a reward. These results indicate that SWD and associated immobility in rats may not reflect the obvious cognitive/behavioral interruption classically associated with absence seizures or CPSs in humans. One interpretation of these results is that human absence seizures and perhaps CPSs could permit a far greater degree of cognitive capacity than often assumed and might be brought under voluntary control in some cases. However, these results also suggest that SWDs and associated immobility may be nonepileptic in healthy outbred rats and reflect instead voluntary rodent behavior unrelated to genetic manipulation or to brain trauma.SIGNIFICANCE STATEMENT Our evidence that inbred and outbred rats learn to control the duration of spike-wave discharges (SWDs) suggests a voluntary behavior with maintenance of consciousness. If SWDs model mild absence seizures and/or complex partial seizures in humans, then an opportunity may exist for operant control complementing or in some cases replacing medication. Their equal occurrence in outbred rats also implies a major potential confound for behavioral neuroscience experiments, at least in adult rats where SWDs are prevalent. Alternatively, the presence and voluntary control of SWDs in healthy outbred rats could indicate that these phenomena do not always model heritable absence epilepsy or post-traumatic epilepsy in humans, and may instead reflect typical rodent behavior.

Impaired consciousness in patients with absence seizures investigated by functional MRI, EEG, and behavioural measures: a cross-sectional study

Background

Absence seizures are brief episodes of impaired consciousness characterized by staring and behavioral arrest. The neural underpinnings of impaired consciousness and of the variable severity of behavioral impairment observed from one absence seizure to the next are not well understood. We therefore compared fMRI and EEG changes in absence seizures with impaired task performance to seizures in which performance was spared.

Methods

Patients were recruited from 59 pediatric neurology practices including hospitals and neurology outpatient offices throughout the United States. We performed simultaneous electroencephalography (EEG), fMRI, and behavioral testing in children and adolescents aged 6 to 19 years with typical absence epilepsy. fMRI and EEG were analyzed using data-driven approaches without prior assumptions about signal time courses or spatial distributions. The main outcomes were fMRI and EEG amplitudes in seizures with impaired versus spared behavioral responses analysed by t-test. We also examined the timing of fMRI and EEG changes in seizures with impaired behavioral responses compared to seizures with spared responses.

Findings

93 patients were enrolled between September 1, 2005 and January 1, 2013, and we captured a total of 1032 seizures in 39 patients. fMRI changes during seizures occurred sequentially in three functional brain networks previously well-validated in studies of normal subjects. Seizures associated with more impaired behavior showed higher fMRI amplitude in all three networks compared to seizures with spared performance. In the default-mode network fMRI, amplitude was 0·57 ± 0·26% for seizures with impaired and 0·40 ± 0·16% for seizures with spared behavioral responses (mean difference 017%; 95% CI: 0·11 to 0·23%; p < 0.0001). In the task-positive network, fMRI amplitude was 0·53 ± 0·29% for impaired and 0·39 ± 0·15% for spared seizures (mean difference 0·14%; 95% CI: 008 to 0·21%; p < 0.0001). In the sensorimotor-thalamic network, fMRI amplitude was 0·41 ± 0·25% for impaired and 0·34 ± 014% for spared seizures (mean difference 0 07%; 95% CI: 001 to 0·13%; p = 0.02). Seizures with impaired behavior also showed greater EEG power in widespread brain regions compared to seizures with spared behavior. Mean fractional EEG power in the frontal leads was 50·4 ± 15·2 for seizures with impaired and 24·8 ± 6·5 for seizures with spared behavior (mean difference 25·6; 95% CI: 210 to 30·3); middle leads 35·4 ± 6·5 for impaired, 13 3 ± 34 for spared seizures (mean difference 22·1; 95% CI: 20.0 to 24·1); posterior leads 41·6 ± 5·3 for impaired, 24·6 ± 86 for spared seizures (mean difference 170; 95% CI: 14·4 to 19·7); p < 00001 for all comparisons. Average seizure duration was longer for seizures with impaired behavior at 79 ± 66 s, compared to 3·8 ± 3.0 s for seizures with spared behavior (mean difference 4.1 s; 95% CI 3.0 to 5.3 s, p < 00001). However, larger amplitude fMRI and EEG signals occurred at the outset or even preceding seizures with impairment.

Interpretation

Impaired consciousness in absence seizures is related to the intensity of physiological changes in established networks affecting widespread regions of the brain. Increased EEG and fMRI amplitude occurs at the onset of seizures associated with behavioral impairment. These findings suggest that a vulnerable state may exist at the initiation of some seizures leading to greater physiological changes and altered consciousness.

Functional Network Connectivity Patterns between Idiopathic Generalized Epilepsy with Myoclonic and Absence Seizures

The extensive cerebral cortex and subcortical structures are considered as the major regions related to the generalized epileptiform discharges in idiopathic generalized epilepsy. However, various clinical syndromes and electroencephalogram (EEG) signs exist across generalized seizures, such as the loss of consciousness during absence seizures (AS) and the jerk of limbs during myoclonic seizures (MS). It is presumed that various functional systems affected by discharges lead to the difference in syndromes of these seizures. Twenty epileptic patients with MS, 21 patients with AS, and 21 healthy controls were recruited in this study. The functional network connectivity was analyzed based on the resting-state functional magnetic resonance imaging scans. The statistical analysis was performed in three groups to assess the difference in the functional brain networks in two types of generalized seizures. Twelve resting-state networks were identified in three groups. Both patient groups showed common abnormalities, including decreased functional connectivity in salience network (SN), cerebellum network, and primary perceptional networks and decreased connection between SN and visual network, compared with healthy controls. Interestingly, the frontal part of high-level cognitive resting-state networks showed increased functional connectivity (FC) in patients with MS, but decreased FC in patients with AS. Moreover, patients with MS showed decreased negative connections between high-level cognitive networks and primary system. The common alteration in both patient groups, including SN, might reflect a similar mechanism associated with the loss of consciousness during generalized seizures. This study provided the evidence of brain network in generalized epilepsy to understand the difference between MS and AS.

Localized shape abnormalities in the thalamus and pallidum are associated with secondarily generalized seizures in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) is a common type of drug-resistant epilepsy and secondarily generalized tonic-clonic seizures (sGTCS) have devastating consequences for patients' safety and quality of life. To probe the mechanism underlying the genesis of sGTCS, we investigated the structural differences between patients with and without sGTCS in a cohort of mTLE with radiologically defined unilateral hippocampal sclerosis. We performed voxel-based morphometric analysis of cortex and vertex-wise shape analysis of subcortical structures (the basal ganglia and thalamus) on MRI of 39 patients (21 with and 18 without sGTCS). Comparisons were initially made between sGTCS and non-sGTCS groups, and subsequently made between uncontrolled-sGTCS and controlled-sGTCS subgroups. Regional atrophy of the ipsilateral ventral pallidum (cluster size=450 voxels, corrected p=0.047, Max voxel coordinate=107, 120, 65), medial thalamus (cluster size=1128 voxels, corrected p=0.049, Max voxel coordinate=107, 93, 67), middle frontal gyrus (cluster size=60 voxels, corrected p<0.05, Max voxel coordinate=-30, 49.5, 6), and contralateral posterior cingulate cortex (cluster size=130 voxels, corrected p<0.05, Max voxel coordinate=16.5, -57, 27) was found in the sGTCS group relative to the non-sGTCS group. Furthermore, the uncontrolled-sGTCS subgroup showed more pronounced atrophy of the ipsilateral medial thalamus (cluster size=1240 voxels, corrected p=0.014, Max voxel coordinate=107, 93, 67) than the controlled-sGTCS subgroup. These findings indicate a central role of thalamus and pallidum in the pathophysiology of sGTCS in mTLE.

Terminal seizure frequency and its relation to SUDEP

BACKGROUND

Sudden unexpected death in epilepsy (SUDEP) is a major cause of death in patients with epilepsy. Several risk factors have been implicated, including early age of onset, tonic-clonic seizures and antiepileptic drugs. However, whether patients who die from SUDEP have a greater frequency of seizures in the few months before death is unclear. We investigated the terminal seizure frequency and its relation to SUDEP among a large group of patients with tonic-clonic seizures in rural West China.

METHODS

We used the database from the Convulsive Epilepsy Control and Management Program in West China, which routinely provides phenobarbital (PB) as a treatment for convulsive epilepsy. Patients with probable SUDEP were included according to pre-set criteria. A verbal autopsy was undertaken for each case. By matching each patient's age, sex, date of joining the program, time in follow-up, and baseline seizure frequency, we set up a 1:5 ratio control group. SPSS 21.0 statistics were applied to compare the differences in seizure frequency 3months prior to SUDEP between patients with probable SUDEP and controls. Furthermore, the dynamic changes of terminal seizure frequency 6-9months, 3-6months, and 3months prior to SUDEP was also analyzed.

RESULTS

A total of 41 patients who died from probable SUDEP were identified out of 7844 patients during 10years of follow-up. The SUDEP group had a significantly higher tonic-clonic seizure frequency 3months before their deaths than the control group (p=0.023). At the same time, their seizure-free rate was lower than the control group (p=0.025). Patients with probable SUDEP who were followed up over 12months were further studied as a subgroup. They had more tonic-clonic seizures 3months prior to death compared to the control group (p=0.010). They also had an increase in seizure frequency in their terminal phase (3months prior) compared to an earlier stage (3-6months prior) (p=0.029). Furthermore, the terminal PB dose in the SUDEP group was higher than the control group (p=0.002).

CONCLUSION

Patients who died from SUDEP had more frequent tonic-clonic seizures 3months before their deaths. Higher seizure frequency increases the exposure to peri-ictal pathophysiological events, which possibly relate to SUDEP. This phenomenon may be due to the drug resistance potential of these patients or the high dose of PB. Further research is required to ascertain the underlying mechanisms of SUDEP.

Altered sleep homeostasis correlates with cognitive impairment in patients with focal epilepsy

In animal studies, both seizures and interictal spikes induce synaptic potentiation. Recent evidence suggests that electroencephalogram slow wave activity during sleep reflects synaptic potentiation during wake, and that its homeostatic decrease during the night is associated with synaptic renormalization and its beneficial effects. Here we asked whether epileptic activity induces plastic changes that can be revealed by high-density electroencephalography recordings during sleep in 15 patients with focal epilepsy and 15 control subjects. Compared to controls, patients with epilepsy displayed increased slow wave activity power during non-rapid eye movement sleep over widespread, bilateral scalp regions. This global increase in slow wave activity power was positively correlated with the frequency of secondarily generalized seizures in the 3-5 days preceding the recordings. Individual patients also showed local increases in sleep slow wave activity power at scalp locations matching their seizure focus. This local increase in slow wave activity power was positively correlated with the frequency of interictal spikes during the last hour of wakefulness preceding sleep. By contrast, frequent interictal spikes during non-rapid eye movement sleep predicted a reduced homeostatic decrease in the slope of sleep slow waves during the night, which in turn predicted reduced daytime learning. Patients also showed an increase in sleep spindle power, which was negatively correlated with intelligence quotient. Altogether, these findings suggest that both seizures and interictal spikes may induce long-lasting changes in the human brain that can be sensitively detected by electroencephalographic markers of sleep homeostasis. Furthermore, abnormalities in sleep markers are correlated with cognitive impairment, suggesting that not only seizures, but also interictal spikes can have negative consequences.