fMRI correlates of interictal epileptic activity in patients with idiopathic benign focal epilepsy of childhood

EEG-fMRI of epileptiform discharges: non-invasive investigation of the whole brain

Simultaneous EEG-fMRI is a unique and non-invasive method for investigating epileptic activity. Interictal epileptiform discharge-related EEG-fMRI provides cortical and subcortical blood oxygen level-dependent (BOLD) signal changes specific to epileptic discharges. As a result, EEG-fMRI has revealed insights into generators and networks involved in epileptic activity in different types of epilepsy, demonstrating-for instance-the implication of the thalamus in human generalized spike and wave discharges and the role of the Default Mode Network (DMN) in absences and focal epilepsy, and proposed a mechanism for the cortico-subcortical interactions in Lennox-Gastaut syndrome discharges. EEG-fMRI can find deep sources of epileptic activity not available to scalp EEG or MEG and provides critical new information to delineate the epileptic focus when considering surgical treatment or electrode implantation. In recent years, methodological advances, such as artifact removal and automatic detection of events have rendered this method easier to implement, and its clinical potential has since been established by evidence of the impact of BOLD response on clinical decision-making and of the relationship between concordance of BOLD responses with extent of resection and surgical outcome. This review presents the recent developments in EEG-fMRI methodology and EEG-fMRI studies in different types of epileptic disorders as follows: EEG-fMRI acquisition, gradient and pulse artifact removal, statistical analysis, clinical applications, pre-surgical evaluation, altered physiological state in generalized genetic epilepsy, and pediatric EEG-fMRI studies.

Involvement of brain structures in childhood epilepsy with centrotemporal spikes

BACKGROUND

We aimed to investigate electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) findings to elucidate the interictal epileptiform discharge (IED)-related functional alterations in deep brain structures and the neocortex in childhood epilepsy with centrotemporal spikes (CECTS).

METHODS

Ten children with CECTS (median age 8.2 years), referred to our hospital within a year of onset, were eligible for inclusion. They underwent EEG-fMRI recording during sleep. Llongitudinal evaluations, including medical examinations, intelligence tests, and questionnaires about developmental disabilities, were performed. The initial evaluation was performed at the same time as the EEG-fMRI, and the second evaluation was performed over 2 years after the initial evaluation.

RESULTS

Three children were unable to maintain sleep during the EEG-fMRI recording, and the remaining seven children were eligible for further assessment. All patients showed unilateral-dominant centrotemporal spikes during scans. One patient had only positive hemodynamic responses, while the others had both positive and negative hemodynamic responses. All patients showed IED-related hemodynamic responses in the bilateral neocortex. For deep brain structures, IED-related hemodynamic responses were observed in the cingulate gyrus (n = 4), basal ganglia (n = 3), thalamus (n = 2), and default mode network (n = 1). Seizure frequencies at the second evaluation were infrequent or absent, and the longitudinal results of intelligence tests and questionnaires were within normal ranges.

CONCLUSIONS

We demonstrated that IEDs affect broad brain areas, including deep brain structures such as the cingulate gyrus, basal ganglia, and thalamus. Deep brain structures may play an important role in the pathophysiology of CECTS.

Interictal epileptiform discharges changed epilepsy-related brain network architecture in BECTS

To investigate directed information flow of epileptiform activity in benign epilepsy with centrotemporal spikes (BECTS) during ictal epileptiform discharges (IEDs) and non-IEDs periods. In this multi-center study, a total of 188 subjects, including 50 BECTS and 138 normal children's controls (NCs) from three different centers (Center 1: females/males, 38/55; mean age, 9.33 ± 2.6 years; Center 2: females/males,7/10; mean age, 8.59 ± 2.32 years; Center 3: females/males, 14/14; mean age, 13 ± 3.42 years) were recruited. The BECTS were classified into IEDs (females/males, 12/15; mean age, 8.15 ± 1.68 years) and non-IEDs (females/males, 10/13; mean age, 9.09 ± 1.98 years) subgroups depending on presence of central-temporal spikes from an EEG-fMRI examination. Three new methods, structural equation parametric modeling, dynamic causal modeling and granger causality density (GCD) were used to determine optimal network architectures for BECTS. Three multicentric NCs determined a reliable and consistent network architecture by structural equation parametric modeling method. Further analyses were used for IEDs and non-IEDs to determine the brain network architecture by structural equation parametric modeling, dynamic causal modeling and GCD, respectively. The brain network architecture of IEDs substate, non-IEDs substate and NCs are different. IEDs promoted the driving effect of the Rolandic areas with more output information flows, and increased the targeted effect of the top of pre-/post-central gyrus with more input information flows. The information flow arises from the Rolandic areas, and subsequently propagates to the top of pre-/post-central gyrus and thalamus. From non-IEDs status to IEDs status, the thalamus load may play an important role in the modulation and regulation of epileptiform activity. These findings shed new light on pathophysiological mechanism of directed localization of epileptiform activity in BECTS.

Reliability and availability of granger causality density in localization of Rolandic focus in BECTS

A new method, called granger causality density (GCD), could reflect the directed information flow of the epileptiform activity, which is much closely match with excitatory and inhibitory imbalance theory of epilepsy. Here, we investigated if GCD could effectively localize the Rolandic focus in 50 patients with benign childhood epilepsy with central-temporal spikes (BECTS) from 27 normal children. The BECTS were classified into ictal epileptiform discharges (IEDs; 12 females, 15 males;age, 8.15 ± 1.68 years) and non-IEDs (10 females, 13 males; age, 9.09 ± 1.98 years) subgroups depending on the presence of central-temporal spikes. Multiple correlation-modality analyses (Pearson, across-voxel and across-subject correlations) were used to calculate the couplings between the GCD maps and IEDs-related brain activation map. The individual lateralization coefficient of localize IEDs and multiple regression analysis were used to identify the reliability of the GCD method in localizing the Rolandic focus. In this study, multiple correlation-modality analyses showed that the IEDs-related brain activation map and the GCD maps had highly temporal (coefficient ׀r\= 0.56 ~ 0.65) and spatial (\r\=0.53~0.91) (r\=~ couplings. The proposed GCD method and multiple regression analyses showed consistent findings with the clinical EEG recordings in lateralization of Rolandic focus. Furthermore, the GCD method could reflect the epilepsy-related brain activity during non-IEDs substate. Therefore, the proposed GCD method has the potential to be served as an effective and reliable neuroimaging biomarker to localize the Rolandic focus of BECTS. These findings are critical for clinical early diagnosis, and may promote the progression of treatment and management of pediatric epilepsy.

Self-limited focal epilepsy decreased regional brain activity in sensorimotor areas

OBJECTIVE

The fractional amplitude of low-frequency fluctuation (fALFF) method was used to identify the regional brain activity deficits of self-limited focal epilepsy with centrotemporal spikes (SLFECS) relative to normal controls (NCs).

METHODS

A total of 21 SLFECS (10 females, 11 males; mean age, 8.57 ± 1.5 years) and 21 status-matched (age, sex, and education) NCs (10 females, 11 males; mean age, 8.76 ± 2.19 years) were recruited. The fALFF method was applied to identify SLFECS-related regional brain alterations. Receiver operating characteristic (ROC) curve was applied to identify the ability of these regional brain areas in distinguishing the SLFECS group from the NCs group. The relationships between the regional brain activity deficits and clinical features were evaluated by Pearson's correlation analysis.

RESULTS

Self-limited focal epilepsy with centrotemporal spikes was associated with widespread regional brain activity alterations, including left cuneus with higher fALFF values, and bilateral striatum, bilateral precentral gyrus, ventral and dorsal pathway of sensory area, left dorsolateral prefrontal cortex, and left Rolandic area with lower fALFF values. ROC curve revealed excellent AUC value (0.964) of these areas in distinguishing the SLFECS group from the NCs group with high degree of sensitivity (90.5%) and specificity (95.2%). Intelligence quotient score positively correlated with the fALFF value in the left striatum (r = 0.453, p = 0.039).

CONCLUSIONS

The fALFF parameter could be served as a potential biomarker to identify the SLFECS-related regional brain deficits in the sensorimotor cortex and their pathways, which may be the etiology of paresthesia in SLFECS.

The Oscillatory Basis of Working Memory Function and Dysfunction in Epilepsy

Working memory (WM) deficits are pervasive co-morbidities of epilepsy. Although the pathophysiological mechanisms underpinning these impairments remain elusive, it is thought that WM depends on oscillatory interactions within and between nodes of large-scale functional networks. These include the hippocampus and default mode network as well as the prefrontal cortex and frontoparietal central executive network. Here, we review the functional roles of neural oscillations in subserving WM and the putative mechanisms by which epilepsy disrupts normative activity, leading to aberrant oscillatory signatures. We highlight the particular role of interictal epileptic activity, including interictal epileptiform discharges and high frequency oscillations (HFOs) in WM deficits. We also discuss the translational opportunities presented by greater understanding of the oscillatory basis of WM function and dysfunction in epilepsy, including potential targets for neuromodulation.

Simultaneous fMRI-EEG-Based Characterisation of NREM Parasomnia Disease: Methods and Limitations

Functional magnetic resonance imaging (fMRI) techniques and electroencephalography (EEG) were used to investigate sleep with a focus on impaired arousal mechanisms in disorders of arousal (DOAs). With a prevalence of 2–4% in adults, DOAs are significant disorders that are currently gaining attention among physicians. The paper describes a simultaneous EEG and fMRI experiment conducted in adult individuals with DOAs (n=10). Both EEG and fMRI data were validated by reproducing well established EEG and fMRI associations. A method for identification of both brain functional areas and EEG rhythms associated with DOAs in shallow sleep was designed. Significant differences between patients and controls were found in delta, theta, and alpha bands during awakening epochs. General linear models of the blood-oxygen-level-dependent signal have shown the secondary visual cortex and dorsal posterior cingulate cortex to be associated with alpha spectral power fluctuations, and the precuneus with delta spectral power fluctuations, specifically in patients and not in controls. Future EEG–fMRI sleep studies should also consider subject comfort as an important aspect in the experimental design.

Pharmacological treatment for continuous spike-wave during slow wave sleep syndrome and Landau-Kleffner Syndrome

BACKGROUND

Continuous spike-wave during slow wave sleep syndrome (CSWS) and Landau-Kleffner syndrome (LKS) are two epileptic encephalopathies that present with neurocognitive regression, aphasia, and clinical seizures, typically presenting in children around five years of age. The pathophysiology of these conditions is not completely understood. Some studies suggest a common origin for both. No systematic reviews have assessed the efficacy of pharmacological interventions for these conditions.

OBJECTIVES

To assess the benefit and adverse effects of pharmacological interventions for the treatment of CSWS and LKS.

SEARCH METHODS

On 8 September 2020, we searched the Cochrane Register of Studies (CRS Web) and MEDLINE Ovid (1946 to September 04, 2020). We applied no language restrictions. CRS Web includes randomised or quasi-randomised, controlled trials from CENTRAL, PubMed, Embase, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform.

SELECTION CRITERIA

Randomised controlled trials, quasi-randomised controlled trials, and cluster-randomised trials comparing antiepileptic drugs alone, or with steroids or intravenous immunoglobulins, or both versus other antiepileptic drugs, or placebo, or no treatment, administered to children with CSWS and LKS. We planned to compare treatments for the two conditions separately.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies identified by the search strategy for inclusion. The primary outcomes considered in this review were neuropsychological-neurolinguistic functions.

MAIN RESULTS

Our search strategy yielded 18 references. Two review authors independently assessed all references. We did not find any completed studies to include. We identified one ongoing trial, which was terminated because of lack of enrolment.

AUTHORS' CONCLUSIONS

There was no evidence from trials to support or refute the use of pharmacological treatment for continuous spike-wave during slow wave sleep syndrome or Landau-Kleffner syndrome. Well-designed randomised controlled trials are needed to inform practice.

The effect of interictal epileptiform discharges on cognitive and academic performance in children with idiopathic epilepsy

Background

Interictal epileptiform discharges (IEDs) have been proven to impair cognitive function. However, it is not clear whether IEDs disrupt academic performance in children with idiopathic epilepsy, and the contribution of cognitive function deficits to impaired academic performance has not been clarified. This study aimed to examine the cognitive deficits and academic impairment in childhood idiopathic epilepsy with IEDs.

Methods

Ninety-seven childhood idiopathic epilepsy with IEDs, 77 childhood idiopathic epilepsy without IEDs, and 71 healthy controls completed a series of cognitive tests. We analyzed the cognitive performance in several domains including language, mathematics, psychomotor speed, spatial ability, memory, general intelligence, attention and executive functioning. Analysis of variance was conducted to compare the performance on all tests between the three groups.

Results

Childhood idiopathic epilepsy with IEDs exhibited not only general cognitive deficits in processing speed, spatial ability, and attention, but also arithmetic impairment. Furthermore, general cognitive deficits could account for the impaired arithmetic performance in childhood idiopathic epilepsy with IEDs.

Conclusions

Our study suggested that IEDs in children with idiopathic epilepsy affected both cognitive function and academic performance, and that the cognitive deficits may be responsible for arithmetic performance impairment.

Epilepsy syndromes of childhood with sleep activation: Insights from functional imaging

In epilepsy syndromes of childhood with sleep activation, defined as the spectrum of epileptic conditions going from classical benign childhood epilepsy with centrotemporal spikes (BECTS) to epileptic encephalopathy (EE) with continuous spike and waves during slow-wave sleep (CSWS) including Landau-Kleffner syndrome (LKS), a lot of functional imaging studies have been performed so far, leading to results that are not always consistent, related to the technique of neuroimaging performed and to the variability of the clinical phenotype. Most consistent findings are, depending of the method used, activations or increased regional glucose metabolism in the epileptogenic regions, and deactivations, hypometabolism or decreased functional connectivity in cortical regions that belong to the default mode network. Functional changes are either transitory, temporally related to the occurrence of interictal epileptiform discharges (IED), or permanent, persisting across IED-free periods. Some studies have shown that the more severe phenotype, i.e. EE with CSWS, displays the more profound functional disturbances. Taken together, functional imaging studies support the concept that IED impact cognition in epilepsy syndromes of childhood with sleep activation. However, the precise chronology between the occurrence of IED and the functional disturbances, the neuropsychological correlates of the functional disturbances, and the effects of the anti-epileptic treatments on IED, functional disturbances and cognition need to be further studied.

Mapping the Effect of Interictal Epileptic Activity Density During Wakefulness on Brain Functioning in Focal Childhood Epilepsies With Centrotemporal Spikes

Childhood epilepsy with centrotemporal spikes (CECTS) is the most common type of “self-limited focal epilepsies.” In its typical presentation, CECTS is a condition reflecting non-lesional cortical hyperexcitability of rolandic regions. The benign evolution of this disorder is challenged by the frequent observation of associated neuropsychological deficits and behavioral impairment. The abundance (or frequency) of interictal centrotemporal spikes (CTS) in CECTS is considered a risk factor for deficits in cognition. Herein, we captured the hemodynamic changes triggered by the CTS density measure (i.e., the number of CTS for time bin) obtained in a cohort of CECTS, studied by means of video electroencephalophy/functional MRI during quite wakefulness. We aim to demonstrate a direct influence of the diurnal CTS frequency on epileptogenic and cognitive networks of children with CECTS. A total number of 8,950 CTS (range between 27 and 801) were recorded in 23 CECTS (21 male), with a mean number of 255 CTS/patient and a mean density of CTS/30 s equal to 10,866 ± 11.46. Two independent general linear model models were created for each patient based on the effect of interest: “individual CTS” in model 1 and “CTS density” in model 2. Hemodynamic correlates of CTS density revealed the involvement of a widespread cortical–subcortical network encompassing the sensory-motor cortex, the Broca's area, the premotor cortex, the thalamus, the putamen, and red nucleus, while in the CTS event-related model, changes were limited to blood–oxygen-level-dependent (BOLD) signal increases in the sensory-motor cortices. A linear relationship was observed between the CTS density hemodynamic changes and both disease duration (positive correlation) and age (negative correlation) within the language network and the bilateral insular cortices. Our results strongly support the critical role of the CTS frequency, even during wakefulness, to interfere with the normal functioning of language brain networks.

BECTS Substate Classification by Granger Causality Density Based Support Vector Machine Model

Objectives: To investigate the performance of substate classification of children with benign epilepsy with centrotemporal spikes (BECTS) by granger causality density (GCD) based support vector machine (SVM) model.

Methods: Forty-two children with BECTS (21 females, 21 males; mean age, 8.6 ± 1.96 years) were classified into interictal epileptic discharges (IEDs; 11 females, 10 males) and non-IEDs (10 females, 11 males) substates depending on presence of central-temporal spikes or not. GCD was calculated on four metrics, including inflow, outflow, total-flow (inflow + outflow) and int-flow (inflow – outflow) connectivity. SVM classifier was applied to discriminate the two substates.

Results: The Rolandic area, caudate, dorsal attention network, visual cortex, language networks, and cerebellum had discriminative effect on distinguishing the two substates. Relative to each of the four GCD metrics, using combined metrics could reach up the classification performance (best value; AUC, 0.928; accuracy rate, 90.83%; sensitivity, 90%; specificity, 95%), especially for the combinations with more than three GCD metrics. Specially, combined the inflow, outflow and int-flow metric received the best classification performance with the highest AUC value, classification accuracy and specificity. Furthermore, the GCD-SVM model received good and stable classification performance across 14 dimension reduced data sets.

Conclusions: The GCD-SVM model could be used for BECTS substate classification, which might have the potential to provide a promising model for IEDs detection. This may help assist clinicians for administer drugs and prognosis evaluation.

Functional and Structural Network Disorganizations in Typical Epilepsy With Centro-Temporal Spikes and Impact on Cognitive Neurodevelopment

Epilepsy with Centrotemporal Spikes (ECTS) is the most common form of self-limited focal epilepsy. The pathophysiological mechanisms by which ECTS induces neuropsychological impairment in 15-30% of affected children remain unclear. The objective of this study is to review the current state of knowledge concerning the brain structural and functional changes that may be involved in cognitive dysfunctions in ECTS. Structural brain imaging suggests the presence of subtle neurodevelopmental changes over the epileptogenic zone and over distant regions in ECTS. This structural remodeling likely occurs prior to the diagnosis and evolves over time, especially in patients with cognitive impairment, suggesting that the epileptogenic processes might interfere with the dynamics of the brain development and/or the normal maturation processes. Functional brain imaging demonstrates profound disorganization accentuated by interictal epileptic spikes (IES) in the epileptogenic zone and in remote networks in ECTS. Over the epileptogenic zone, the literature demonstrates changes in term of neuronal activity and synchronization, which are effective several hundred milliseconds before the IES. In the same time window, functional changes are also observed in bilateral distant networks, notably in the frontal and temporal lobes. Effective connectivity demonstrates that the epileptogenic zone constitutes the key area at the origin of IES propagation toward distant cortical regions, including frontal areas. Altogether, structural and functional network disorganizations, in terms of: (i) power spectral values, (ii) functional and effective connectivity, are likely to participate in the cognitive impairment commonly reported in children with ECTS. These results suggest a central and causal role of network disorganizations related to IES in the neuropsychological impairment described in ECTS children.

Epileptic Discharge Related Functional Connectivity Within and Between Networks in Benign Epilepsy with Centrotemporal Spikes

Benign epilepsy with centrotemporal spikes (BECTS) is a common childhood epilepsy syndrome associated with abnormalities in neurocognitive domains, particularly during interictal epileptiform discharges (IEDs). Here, we investigated the effects of IEDs on brain’s intrinsic connectivity networks in 43 BECTS patients and 28 matched healthy controls (HCs). Patients were further divided into IED and non-IED subgroups based on simultaneous EEG-fMRI recordings. Functional connectivity within and between five networks, corresponding to seizure origination and cognitive processes, were analyzed to measure IED effects. We found that patients exhibited increased connectivity within the auditory network (AN) and the somato-motor network (SMN), and decreased connectivity within the basal ganglia network and the dorsal attention network, suggesting that both transient and chronic seizure activity may disturb normal network organization. The IED group showed decreased functional connectivity within the default mode network (DMN) compared with the non-IED group and HCs, implying that the DMN was selectively impaired during epileptiform discharges associated with altered self-referential cognitive functions. Moreover, the IED group exhibited increased positive correlations between the AN and the SMN, which suggests a possible excessive influence of centrotemporal spiking on information processing in the auditory system. The association between epileptic activity and network dysfunctions highlights their importance in investigating the pathological mechanism underlying BECTS.

Extrastriate visual cortex in idiopathic occipital epilepsies: The contribution of retinotopic areas to spike generation

OBJECTIVES

To provide insight into the pathophysiology of idiopathic childhood occipital epilepsies (ICOEs), by mapping the contribution of retinotopic visual areas to the generation and sustainment of epileptic activity.

METHODS

Thirteen patients affected by ICOEs (mean age = 10.9 years) underwent a video electroencephalography-functional magnetic resonance imaging (EEG-fMRI) study. A flexible-related fMRI analysis was applied to estimate the shape of the blood oxygen level-dependent (BOLD) response in each patient. Second-level analysis was performed using the interictal EEG discharge (IED)-specific response shape for the ICOE group. The resulting fMRI t-maps were warped to the Population-Average, Landmark- and Surface-based (PALS)-B12 atlas in Caret. For localization purposes, functional results were plotted and compared against 19 retinotopic areas for each hemisphere. A correlation analysis was performed between the hemodynamic maps and electroclinical variables.

RESULTS

The shape of the group-averaged hemodynamic response in ICOE patients showed an earlier time-to-peak and a more pronounced undershoot than the canonical hemodynamic response function (HRF). The random-effect analysis showed positive hemodynamic changes in the bilateral temporooccipital network. With regard to the retinotopic subdivision of the visual cortex, the primary visual area was consistently spared. Conversely, an extensive involvement of the occipitotemporal cortex, including the fusiform gyrus, and the occipitoparietal areas was observed. Moreover, a linear relationship was detected between the occipital spike-density and BOLD increases at the postcentral gyrus and temporooccipital cortex.

SIGNIFICANCE

Our data indicate that both the ventral and dorsal visual pathways are involved in spike generation in ICOEs, to extents that vary between patients, and reinforce the concept of benign childhood seizure susceptibility syndrome as a substrate for ICOEs. Finally, these results underscore the need for appropriate neuropsychological testing in these children, aimed at revealing selective impairments in functions subserved by both visual pathways.

Local Activity and Causal Connectivity in Children with Benign Epilepsy with Centrotemporal Spikes

The aim of the current study was to localize the epileptic focus and characterize its causal relation with other brain regions, to understand the cognitive deficits in children with benign childhood epilepsy with centrotemporal spikes (BECTS). Resting-state functional magnetic resonance imaging (fMRI) was performed in 37 children with BECTS and 25 children matched for age, sex and educational achievement. We identified the potential epileptogenic zone (EZ) by comparing the amplitude of low frequency fluctuation (ALFF) of spontaneous blood oxygenation level dependent fMRI signals between the groups. Granger causality analysis was applied to explore the causal effect between EZ and the whole brain. Compared with controls, children with BECTS had significantly increased ALFF in the right postcentral gyrus and bilateral calcarine, and decreased ALFF in the left anterior cingulate cortex, bilateral putaman/caudate, and left cerebellum. ALFF values in the putaman/caudate were positively correlated with verbal IQ scores in patients. The ALFF values in cerebellum and performance IQ scores were negatively correlated in patients. These results suggest that ALFF disturbances in the putaman/caudate and cerebellum play an important role in BECTS cognitive dysfunction. Compared with controls, the patients showed increased driving effect from the EZ to the right medial frontal cortex and posterior cingulate cortex and decreased causal effects from the EZ to left inferior frontal gyrus. The causal effect of the left inferior frontal gyrus negatively correlated with disease duration, which suggests a relation between the epileptiform activity and language impairment. All together, these findings provide additional insight into the neurophysiological mechanisms of epilepitogenisis and cognitive dysfunction associated with BECTS.

Intrinsic brain activity as a diagnostic biomarker in children with benign epilepsy with centrotemporal spikes

Benign epilepsy with centrotemporal spikes (BECTS) is often associated with neural circuit dysfunction, particularly during the transient active state characterized by interictal epileptiform discharges (IEDs). Little is known, however, about the functional neural circuit abnormalities in BECTS without IEDs, or if such abnormalities could be used to differentiate BECTS patients without IEDs from healthy controls (HCs) for early diagnosis. To this end, we conducted resting-state functional magnetic resonance imaging (RS-fMRI) and simultaneous Electroencephalogram (EEG) in children with BECTS (n = 43) and age-matched HC (n = 28). The simultaneous EEG recordings distinguished BECTS with IEDs (n = 20) from without IEDs (n = 23). Intrinsic brain activity was measured in all three groups using the amplitude of low frequency fluctuation at rest. Compared to HC, BECTS patients with IEDs exhibited an intrinsic activity abnormality in the thalamus, suggesting that thalamic dysfunction could contribute to IED emergence while patients without IEDs exhibited intrinsic activity abnormalities in middle frontal gyrus and superior parietal gyrus. Using multivariate pattern classification analysis, we were able to differentiate BECTS without IEDs from HCs with 88.23% accuracy. BECTS without epileptic transients can be distinguished from HC and BECTS with IEDs by unique regional abnormalities in resting brain activity. Both transient abnormalities as reflected by IEDs and chronic abnormalities as reflected by RS-fMRI may contribute to BECTS development and expression. Intrinsic brain activity and multivariate pattern classification techniques are promising tools to diagnose and differentiate BECTS syndromes. Hum Brain Mapp 36:3878-3889, 2015. © 2015 Wiley Periodicals, Inc.

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.

Mapping (and modeling) physiological movements during EEG-fMRI recordings: the added value of the video acquired simultaneously

BACKGROUND

During resting-state EEG-fMRI studies in epilepsy, patients' spontaneous head-face movements occur frequently. We tested the usefulness of synchronous video recording to identify and model the fMRI changes associated with non-epileptic movements to improve sensitivity and specificity of fMRI maps related to interictal epileptiform discharges (IED).

NEW METHODS

Categorization of different facial/cranial movements during EEG-fMRI was obtained for 38 patients [with benign epilepsy with centro-temporal spikes (BECTS, n=16); with idiopathic generalized epilepsy (IGE, n=17); focal symptomatic/cryptogenic epilepsy (n=5)]. We compared at single subject- and at group-level the IED-related fMRI maps obtained with and without additional regressors related to spontaneous movements. As secondary aim, we considered facial movements as events of interest to test the usefulness of video information to obtain fMRI maps of the following face movements: swallowing, mouth-tongue movements, and blinking.

RESULTS

Video information substantially improved the identification and classification of the artifacts with respect to the EEG observation alone (mean gain of 28 events per exam).

COMPARISON WITH EXISTING METHOD

Inclusion of physiological activities as additional regressors in the GLM model demonstrated an increased Z-score and number of voxels of the global maxima and/or new BOLD clusters in around three quarters of the patients. Video-related fMRI maps for swallowing, mouth-tongue movements, and blinking were comparable to the ones obtained in previous task-based fMRI studies.

CONCLUSIONS

Video acquisition during EEG-fMRI is a useful source of information. Modeling physiological movements in EEG-fMRI studies for epilepsy will lead to more informative IED-related fMRI maps in different epileptic conditions.

Altered regional homogeneity in rolandic epilepsy: a resting-state FMRI study

Children with rolandic epilepsy (RE) are often associated with cognitive deficits and behavioral problems. Findings from neurophysiological and neuroimaging studies in RE have now demonstrated dysfunction not only in rolandic focus, but also in distant neuronal circuits. Little is known, however, about whether there is distributed abnormal spontaneous brain activity in RE. Using resting-state functional magnetic resonance imaging (RS-fMRI), the present study aimed to determine whether children with RE show abnormal local synchronization during resting state and, if so, whether these changes could be associated with the behavioral/clinical characteristics of RE. Regional homogeneity (ReHo) in children with RE (n = 30) and healthy children (n = 20) was computed on resting-state functional MRI data. In comparison with healthy children, children with RE showed increased ReHo in the central, premotor, and prefrontal regions, while they showed decreased ReHo in bilateral orbitofrontal cortex and temporal pole. In addition, the ReHo value in the left orbitofrontal cortex negatively was corrected with performance intelligence quotient in the children with RE. The aberrant local synchronization, not strictly related to primary site of the typical rolandic focus, indicates the neuropathophysiological mechanism of RE. The study findings may shed new light on the understanding of neural correlation of neuropsychological deficiencies in the children with RE.

EEG-fMRI in atypical benign partial epilepsy

Atypical benign partial epilepsy (ABPE) is a subgroup among the idiopathic focal epilepsies of childhood. Aim of this study was to investigate neuronal networks underlying ABPE and compare the results with previous electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) studies of related epilepsy syndromes. Ten patients with ABPE underwent simultaneous EEG-fMRI recording. In all 10 patients several types of interictal epileptiform discharges (IEDs) were recorded. Individual IED-associated blood oxygen level-dependent (BOLD) signal changes were analyzed in a single subject analysis for each IED type (33 studies). A group analysis was also performed to determine common BOLD signal changes across the patients. IED-associated BOLD signal changes were found in 31 studies. Focal BOLD signal changes concordant with the spike field (21 studies) and distant cortical and subcortical BOLD signal changes (31 studies) were detected. The group analysis revealed a thalamic activation. This study demonstrated that ABPE is characterized by patterns similar to studies in rolandic epilepsy (focal BOLD signal changes in the spike field) as well as patterns observed in continuous spikes and waves during slow sleep (CSWS) (distant BOLD signal changes in cortical and subcortical structures), thereby underscoring that idiopathic focal epilepsies of childhood form a spectrum of overlapping syndromes.

Simultaneous EEG and fMRI recordings (EEG-fMRI) in children with epilepsy

By combining electroencephalography (EEG) with functional magnetic resonance imaging (fMRI) it is possible to describe blood oxygenation level-dependent (BOLD) signal changes related to EEG patterns. This way, EEG-pattern-associated networks of hemodynamic changes can be detected anywhere in the brain with good spatial resolution. This review summarizes EEG-fMRI studies that have been performed in children with epilepsy. EEG-fMRI studies in focal epilepsy (structural and nonlesional cases, benign epilepsy with centrotemporal spikes), generalized epilepsy (especially absence epilepsy), and epileptic encephalopathies (West syndrome, Lennox-Gastaut syndrome, continuous spike and waves during slow sleep, and Dravet syndrome) are presented. Although EEG-fMRI was applied mainly to localize the region presumably generating focal interictal discharges in focal epilepsies, EEG-fMRI identified underlying networks in patients with generalized epilepsies and thereby contributed to a better understanding of these epilepsies. In epileptic encephalopathies a specific fingerprint of hemodynamic changes associated with the particular syndrome was detected. The value of the EEG-fMRI technique for diagnosis and investigation of pathogenetic mechanisms of different forms of epilepsy is discussed.

Pediatric focal epilepsy syndromes

Benign epilepsy with centrotemporal spikes, early-onset childhood occipital epilepsy (Panayiotopoulos syndrome [PS]) and late-onset childhood occipital epilepsy (Gastaut type [LOCE-G]) are the principal pediatric focal epilepsy syndromes. They share major common characteristics: the appearance and resolution of electroclinical features are age related, there is a strong genetic predisposition, the clinical course is often mild with infrequent and easy to control seizures, interictal epileptiform activity is disproportionately abundant when compared with the clinical correlate, and tends to potentiate and generalize during sleep. In this review, we outline the relevant pathophysiology underlying this electroclinical spectrum. Then, the initial description of individual syndromes is followed by a summary of overlapping features and intermediate presentations that question the boundaries between these entities and provide the basis for the concept of a childhood seizure susceptibility syndrome. Additionally, we outline the main features of the related epileptic encephalopathies. An outlook on potential future lines of research completes this review.

Cognitive effects of interictal epileptiform discharges in children

Frequent interictal epileptiform discharges (IEDs) may have effects on cognition. We analysed a group of 182 children with different epilepsy syndromes as well as children with IEDs without observed seizures [corrected], with 24-h ambulatory EEG and cognitive tests. The IED index was estimated, in wakefulness and in sleep, as percentage of time in five categories (0%, <1%, 1-10%, ≥10-50% and ≥50%). IEDs were defined as spikes or spike-wave complexes, isolated or occurring serially (in runs) without evident clinical signs of a seizure. The IED categories were correlated to cognitive test results and epilepsy characteristics. The group of patients with diurnal IEDs in ≥10% of the EEG record showed impaired central information processing speed, short-term verbal memory and visual-motor integration. This effect was seen independently from other EEG-related and epilepsy-related characteristics, and independently from epilepsy syndrome diagnosis. The impact of the nocturnal IEDs was of less importance; only contributing partially to the slowing of central information processing speed. We conclude that frequent IEDs (in more than 10% of the record) in the awake EEG can impair cognitive performance in children. Whether children with a high diurnal spike frequency and low seizure frequency can benefit from antiepileptic treatment should be examined in controlled trials.

Reading performance in children with rolandic epilepsy correlates with nocturnal epileptiform activity, but not with epileptiform activity while awake

OBJECTIVE

An association between language impairment and rolandic epilepsy is frequently reported. This impairment could be correlated with the amount of nocturnal epileptiform activity.

METHODS

We retrospectively analyzed 26 children with rolandic epilepsy and/or rolandic spikes. All had undergone a 24-hour EEG and neuropsychological assessment within 2 weeks. Reading performance (reading words and sentences) and intelligence were measured.

RESULTS

There was a significant negative correlation between amount of nocturnal epileptiform activity and reading sentences R=-0.525 (P=0.008). There was a trend in this correlation for reading words R=-0.398 (P=0.054). We found a negative correlation between amount of nocturnal epileptiform activity and Verbal IQ (R=-0.51 P=0.08). No correlation was found between reading performance or Verbal IQ and amount of diurnal epileptiform activity.

CONCLUSIONS

Reading performance is impaired in children with rolandic epilepsy and is correlated with the amount of nocturnal epileptiform activity.

Neuroimaging findings in children with benign focal epileptiform discharges

PURPOSE

To determine reasons for neuroimaging and neuroimaging findings in children with benign focal epileptiform discharges (BFEDs).

METHODS

We performed a retrospective chart review of children who had BFEDs on routine EEG and underwent brain MRI.

RESULTS

We identified 97 patients with BFEDs and MRI. Forty-five of these 97 patients also had seizures consistent with benign focal epilepsy of childhood with centrotemporal spikes (BECTS). Rationale for imaging in the 45 BECTS patients included historical features such as headaches (14), increase in seizure frequency (5), and new events (5). Nine MRIs were obtained prior to referral and 12 for unspecified reasons. MRI findings were not significantly different between BECTS and BFEDs patients. Fourty-one patients (42%) had abnormal findings on MRI, including T2 hyperintensities (10), hippocampal atrophy (6), malformation of cortical development (4), volume loss (5), Chiari malformation (4), and others (18).

CONCLUSION

MRIs are not routinely recommended in patients with BECTS unless atypical features are present. Atypical features which may prompt MRI include change in clinical seizure types or frequency, historical features such as headaches, abnormal neurological exam, and atypical EEG features. 42% of our selected patients had intracranial abnormalities, most of which were of unclear clinical significance. Remote infarcts and early lesions accounted for most MRI findings suggesting they may be related to BFEDs.

EEG-fMRI coregistration in non-ketotic hyperglycemic occipital seizures

We report the first case, to our knowledge, of non-ketotic hyperglycemic (NKH) related occipital seizures studied by continuous EEG-fMRI in an undiagnosed diabetic patient. Ictal EEG showed left posterior spikes and sharp-waves. Seizures subsided after insulin therapy was started. Continuous EEG-fMRI was performed and BOLD activation was identified in the left Brodmann's area 18 (visual association area). Activation of an epileptic focus related with the patient's metabolic disturbance can be postulated.

Cortical hyperexcitability and epileptogenesis: Understanding the mechanisms of epilepsy - part 2

Epilepsy encompasses a diverse group of seizure disorders caused by a variety of structural, cellular and molecular alterations of the brain primarily affecting the cerebral cortex, leading to recurrent unprovoked epileptic seizures. In this two-part review we examine the mechanisms underlying normal neuronal function and those predisposing to recurrent epileptic seizures starting at the most basic cellular derangements (Part 1, Volume 16, Issue 3) and working up to the highly complex epileptic networks and factors that modulate the predisposition to seizures (Part 2). We attempt to show that multiple factors can modify the epileptic process and that different mechanisms underlie different types of epilepsy, and in most situations there is an interplay between multiple genetic and environmental factors.