Cortico-striatal synchronization in human focal seizures

[Insular lobe epilepsy. Part 1: semiology]

The insula is often referred to as "the fifth lobe" of the brain, and its accessibility used to be very limited due to the deep location under the opercula as well as the sylvian vasculature. It was not until the availability of modern stereo-electroencephalography (SEEG) technique that the intracranial electrodes could be safely and chronically implanted within the insula, thereby enabling anatomo-electro-clinical correlations in seizures of this deep origin. Since the first report of SEEG-recorded insular seizures in late 1990s, the knowledge of insular lobe epilepsy (ILE) has rapidly expanded. Being on the frontline for the diagnosis and management of epilepsy, neurologists should have a precise understanding of ILE to differentiate it from epilepsies of other lobes or non-epileptic conditions. Owing to the multimodal nature and rich anatomo-functional connections of the insula, ILE has a wide range of clinical presentations. The following symptoms should heighten the suspicion of ILE: somatosensory symptoms involving a large/bilateral cutaneous territory or taking on thermal/painful character, and cervico-laryngeal discomfort. The latter ranges from slight dyspnea to a strong sensation of strangulation (laryngeal constriction). Other symptoms include epigastric discomfort/nausea, hypersalivation, auditory, vestibular, gustatory, and aphasic symptoms. However, most of these insulo-opercular symptoms can easily be masked by those of extra-insular seizure propagation. Indeed, sleep-related hyperkinetic (hypermotor) epilepsy (SHE) is a common clinical presentation of ILE, which shows predominant hyperkinetic and/or tonic-dystonic features that are often indistinguishable from those of fronto-mesial seizures. Subtle objective signs, such as constrictive throat noise (i.e., laryngeal constriction) or aversive behavior (e.g., facial grimacing suggesting pain), are often the sole clue in diagnosing insular SHE. Insular-origin seizures should also be considered in temporal-like seizures without frank anatomo-electro-clinical correlations. All in all, ILE is not the epilepsy of an isolated island but rather of a crucial hub involved in the multifaceted roles of the brain.

Involvement of the contralateral hippocampus in ictal-like but not interictal epileptic activities in the kainate mouse model of temporal lobe epilepsy

OBJECTIVE

Animal and human studies have shown that the seizure-generating region is vastly dependent on distant neuronal hubs that can decrease duration and propagation of ongoing seizures. However, we still lack a comprehensive understanding of the impact of distant brain areas on specific interictal and ictal epileptic activities (e.g., isolated spikes, spike trains, seizures). Such knowledge is critically needed, because all kinds of epileptic activities are not equivalent in terms of clinical expression and impact on the progression of the disease.

METHODS

We used surface high-density electroencephalography and multisite intracortical recordings, combined with pharmacological silencing of specific brain regions in the well-known kainate mouse model of temporal lobe epilepsy. We tested the impact of selective regional silencing on the generation of epileptic activities within a continuum ranging from very transient to more sustained and long-lasting discharges reminiscent of seizures.

RESULTS

Silencing the contralateral hippocampus completely suppresses sustained ictal activities in the focus, as efficiently as silencing the focus itself, but whereas focus silencing abolishes all focus activities, contralateral silencing fails to control transient spikes. In parallel, we observed that sustained focus epileptiform discharges in the focus are preceded by contralateral firing and more strongly phase-locked to bihippocampal delta/theta oscillations than transient spiking activities, reinforcing the presumed dominant role of the contralateral hippocampus in promoting long-lasting, but not transient, epileptic activities.

SIGNIFICANCE

Altogether, our work provides suggestive evidence that the contralateral hippocampus is necessary for the interictal to ictal state transition and proposes that crosstalk between contralateral neuronal activity and ipsilateral delta/theta oscillation could be a candidate mechanism underlying the progression from short- to long-lasting epileptic activities.

Stereoelectroencephalography of the Deep Brain: Basal Ganglia and Thalami

SUMMARY

Stereoelectroencephalography (SEEG) has emerged as a transformative tool in epilepsy surgery, shedding light on the complex network dynamics involved in focal epilepsy. This review explores the role of SEEG in elucidating the role of deep brain structures, namely the basal ganglia and thalamus, in epilepsy. SEEG advances understanding of their contribution to seizure generation, propagation, and control by permitting precise and minimally invasive sampling of these brain regions. The basal ganglia, comprising the subthalamic nucleus, globus pallidus, substantia nigra, and striatum, have gained recognition for their involvement in both focal and generalized epilepsy. Electrophysiological recordings reveal hyperexcitability and increased synchrony within these structures, reinforcing their role as critical nodes within the epileptic network. Furthermore, low-frequency and high-frequency stimulation of the basal ganglia have demonstrated potential in modulating epileptogenic networks. Concurrently, the thalamus, a key relay center, has garnered prominence in epilepsy research. Disrupted thalamocortical connectivity in focal epilepsy underscores its significance in seizure maintenance. The thalamic subnuclei, including the anterior nucleus, centromedian, and medial pulvinar, present promising neuromodulatory targets, suggesting pathways for personalized epilepsy therapies. The prospect of multithalamic SEEG and thalamic SEEG stimulation trials has the potential to revolutionize epilepsy management, offering tailored solutions for challenging cases. SEEG's ability to unveil the dynamics of deep brain structures in epilepsy promises enhanced and personalized epilepsy care in our new era of precision medicine. Until deep brain SEEG is accepted as a standard of care, a rigorous informed consent process remains paramount for patients for whom such an exploration is proposed.

Selective striatal fast-spiking interneuron inhibition induces cortical seizure

Whether striatal fast-spiking interneurons are involved in cortical synchronization remains elusive. We performed acute microinjections of a selective FSI-AMPA receptor antagonist into the sensorimotor striatum of non-human primates to verify whether selective FSI inhibition within the sensorimotor striatum could potentially modify cortical excitability, thereby triggering focal seizures. Experiments were performed on three fascicularis monkeys. During each experimental session, low volumes of IEM-1460 (4-8 μL) were injected slowly at 1 μL/min. Spontaneous behavioral changes were classified according to the Racine scale modified for primates. These induced motor behaviors were correlated with electroencephalographic (EEG and EMG) measures. Power spectrum and time-frequency analysis were performed and compared between each period of interest. Pharmacological selective inhibition of striatal fast-spiking INs induced focal motor seizures. Back averaging confirmed that myoclonic activity was closely linked to cortical spikes-and-waves epileptic activity, with a significant increase in cortical EEG power in all studied frequency bands (p < .0001). Thus, striatal FSIs likely play a role in controlling cortical excitability through the cortico-striato-thalamo-cortical pathway. They may contribute to the pathophysiology of focal motor epilepsies by modulating the threshold at which focal motor seizures are triggered.

Dynamic evolution of the anterior cingulate-insula network during seizures

OBJECTIVES

In physiological situations, the anterior cingulate cortex (ACC) and anterior insular cortex (AIC) are prone to coactivation. The functional connectivity and interaction between ACC and AIC in the context of epilepsy remain unclear. This study aimed to investigate the dynamic coupling between these two brain regions during seizures.

METHODS

Patients who underwent stereoelectroencephalography (SEEG) recording were included in this study. The SEEG data were visually inspected and quantitatively analyzed. The narrowband oscillations and aperiodic components at seizure onset were parameterized. The frequency-specific non-linear correlation analysis was applied to the functional connectivity. The excitation/inhibition ratio (E:I ratio) reflected by the aperiodic slope was performed to evaluate the excitability.

RESULTS

Twenty patients were included in the study, with 10 diagnosed with anterior cingulate epilepsy and 10 with anterior insular epilepsy. In both types of epilepsy, the correlation coefficient (h2 ) between the ACC and AIC at seizure onset exhibited a significantly higher value than that during interictal and preictal periods (p < 0.05). The direction index (D) showed a significant increase at seizure onset, serving as an indicator for the direction of information flow between these two brain regions with up to 90% accuracy. The E:I ratio increased significantly at seizure onset, with the seizure-onset zone (SOZ) demonstrating a more pronounced increase compared to non-SOZ (p < 0.05). For seizures originating from AIC, the E:I ratio was significantly higher in the AIC than in the ACC (p = 0.0364).

CONCLUSIONS

In the context of epilepsy, the ACC and AIC are dynamically coupled during seizures. The functional connectivity and excitability exhibit a significant increase at seizure onset. By analyzing connectivity and excitability, the SOZ in ACC and AIC can be identified. The direction index (D) serves as an indicator for the direction of information flow from SOZ to non-SOZ. Notably, the excitability of SOZ changes more significantly than that of non-SOZ.

Abolition of seizures following Forel-H-tomy for drug-resistant epilepsy: A case report

A 62-year-old female experienced an extensive cerebral contusion in the left frontotemporal lobe due to an acute subdural hematoma at the age of 44 years. Six months after the injury, the patient developed epileptic seizures. The seizures were generalized with right cervical rotation and fencing posture. Despite prescriptions for four antiepileptic drugs, partial seizures occurred several times a month and focal to bilateral tonic-clonic seizures once every 2 months. Video-electroencephalography showed epileptic discharges in the left frontal lobe. The patient was subsequently referred to our department for palliative surgery. The patient underwent a left Forel-H-tomy. The prescription of antiepileptic drugs was not changed, and the patient was seizure free for 1 year. Forel-H-tomy, a surgical procedure for intractable epilepsy, was pioneered by Dennosuke Jinnai. Despite its previously reported remarkable efficacy, Forel-H-tomy has not been performed for several decades. Nevertheless, it remains a potential alternative treatment option for drug-resistant epilepsy.

Aberrant structural rich club organization in temporal lobe epilepsy with focal to bilateral tonic-clonic seizures

OBJECTIVE

The purpose of this study was to assess the differences of topological characteristic and rich club organization between temporal lobe epilepsy (TLE) patients with focal seizure (FS) only and those with focal to bilateral tonic-clonic seizures (FBTCS).

METHODS

We recruited 130 unilateral TLE patients, of which 57 patients with FS only and 73 patients with both FS and FBTCS, and 68 age- and gender-matched healthy controls (HC). Whole-brain networks were constructed based on diffusion weighted imaging data. Graph theory was applied to quantify the topological network metrics and rich club organization. Network-based statistic (NBS) analysis was administered to investigate the difference in edge-wise connectivity strength. The non-parametric permutation test was applied to evaluate the differences between groups. Benjamini-Hochberg FDR at the alpha of 5% was carried out for multiple comparations.

RESULTS

In comparison with HC, both the FS and FBTCS group displayed a significant reduction in whole-brain connectivity strength and global efficiency. The FBTCS group showed lower connectivity strength both in the rich club and feeder connections compared to HC. The FS group had lower connectivity strength in the feeder and local connections compared to HC. NBS analysis revealed a wider range of decreased connectivity strength in the FBTCS group, involving 90% of the rich club regions, mainly affecting temporal-subcortical, frontal-parietal, and frontal-temporal lobe, the majority decreasing connections were between temporal lobe and stratum. While the decreased connectivity strength in the FS group were relatively local, involving 50% of rich club regions, mainly concentrated on the temporal-subcortical lobe.

CONCLUSIONS

Network integration was reduced in TLE. TLE with FBTCS selectively disrupted the rich club regions, while TLE with FS only were more likely to affect the non-rich club regions, emphasizing the contribution of rich club organization to seizure generalization.

Stop being so superficial: subcortical disconnection and long-term seizure outcomes

This scientific commentary refers to ‘Thalamostriatal disconnection underpins long-term seizure freedom in frontal lobe epilepsy surgery’ by Giampiccolo et al. (https://doi.org/10.1093/brain/awad085).

Connectivity and Excitability Shape Seizure Circuits

Mapping neuronal circuits that generate focal to bilateral tonic-clonic seizures is essential for understanding general principles of seizure propagation and modifying the risk of death and injury due to bilateral motor seizures. We used novel techniques developed over the past decade to study these circuits. We propose the general hypothesis that at the mesoscale, seizures follow anatomical projections of the seizure focus, preferentially activating more excitable neurons.

The anterior and pulvinar thalamic nuclei interactions in mesial temporal lobe seizure networks

OBJECTIVE

To evaluate the respective roles of the anterior thalamic nucleus (ANT) and the medial pulvinar (PuM) during mesial temporal lobe seizures recorded by stereoelectroencephalography (SEEG).

METHODS

We assessed functional connectivity (FC) in 15 SEEG recorded seizures from 6 patients using a non-linear correlation method. Functional interactions were explored between the mesial temporal region, the temporal neocortex, ANT and PuM. The node total-strength (the summed connectivity of the node with all other nodes) as well as the directionality of the links (IN and OUT strengths) were calculated to estimate drivers and receivers during the cortico-thalamic interactions.

RESULTS

Significant increased thalamo-cortical FC during seizures was observed, with the node total-strength reaching a maximum at seizure end. There was no significant difference in global connectivity values between ANT and PuM. Regarding directionality, significantly higher thalamic IN strength values were observed. However, compared to ANT, PuM appeared to be the driver at the end of seizures with synchronous termination.

CONCLUSIONS

This work demonstrates that during temporal seizures, both thalamic nuclei are highly connected with the mesial temporal region and that PuM could play a role in seizure termination.

SIGNIFICANCE

Understanding functional connectivity between the mesial temporal and thalamic nuclei could contribute to the development of target-specific deep brain stimulation strategies for drug-resistant epilepsy.

Shared functional network abnormality in patients with temporal lobe epilepsy and their siblings

AIM

Temporal lobe epilepsy is a neurological network disease in which genetics played a greater role than previously appreciated. This study aimed to explore shared functional network abnormalities in patients with sporadic temporal lobe epilepsy and their unaffected siblings.

METHODS

Fifty-eight patients with sporadic temporal lobe epilepsy, 13 unaffected siblings, and 30 healthy controls participated in this cross-sectional study. We examined the task-based whole-brain functional network topology and the effective functional connectivity between networks identified by group-independent component analysis.

RESULTS

We observed increased global efficiency, decreased clustering coefficiency, and decreased small-worldness in patients and siblings (p < 0.05, false discovery rate-corrected). The effective network connectivity from the ventral attention network to the limbic system was impaired (p < 0.001, false discovery rate-corrected). These features had higher prevalence in unaffected siblings than in normal population and was not correlated with disease burden. In addition, topological abnormalities had a high intraclass correlation between patients and their siblings.

CONCLUSION

Patients with temporal lobe epilepsy and their unaffected siblings showed shared topological functional disturbance and the effective functional network connectivity impairment. These abnormalities may contribute to the pathogenesis that promotes the susceptibility of seizures and language decline in temporal lobe epilepsy.

Brain lesion locations associated with secondary seizure generalization in tumors and strokes

Structural brain lesions are the most common cause of adult-onset epilepsy. The lesion location may contribute to the risk for epileptogenesis, but whether specific lesion locations are associated with a risk for secondary seizure generalization from focal to bilateral tonic-clonic seizures, is unknown. We identified patients with a diagnosis of adult-onset epilepsy caused by an ischemic stroke or a tumor diagnosed at the Turku University Hospital in 2004-2017. Lesion locations were segmented on patient-specific MR imaging and transformed to a common brain atlas (MNI space). Both region-of-interest analyses (intersection with the cortex, hemisphere, and lobes) and voxel-wise analyses were conducted to identify the lesion locations associated with focal to bilateral tonic-clonic compared to focal seizures. We included 170 patients with lesion-induced epilepsy (94 tumors, 76 strokes). Lesions predominantly localized in the cerebral cortex (OR 2.50, 95% C.I. 1.21-5.15, p = .01) and right hemisphere (OR 2.22, 95% C.I. 1.17-4.20, p = .01) were independently associated with focal to bilateral tonic-clonic seizures. At the lobar-level, focal to bilateral tonic-clonic seizures were associated with lesions in the right frontal cortex (OR 4.41, 95% C.I. 1.44-13.5, p = .009). No single voxels were significantly associated with seizure type. These effects were independent of lesion etiology. Our results demonstrate that lesion location is associated with the risk for secondary generalization of epileptic seizures. These findings may contribute to identifying patients at risk for focal to bilateral tonic-clonic seizures.

Multilayer brain networks can identify the epileptogenic zone and seizure dynamics

Seizure generation, propagation, and termination occur through spatiotemporal brain networks. In this paper, we demonstrate the significance of large-scale brain interactions in high-frequency (80-200Hz) for the identification of the epileptogenic zone (EZ) and seizure evolution. To incorporate the continuity of neural dynamics, here we have modeled brain connectivity constructed from stereoelectroencephalography (SEEG) data during seizures using multilayer networks. After introducing a new measure of brain connectivity for temporal networks, named multilayer eigenvector centrality (mlEVC), we applied a consensus hierarchical clustering on the developed model to identify the EZ as a cluster of nodes with distinctive brain connectivity in the ictal period. Our algorithm could successfully predict electrodes inside the resected volume as EZ for 88% of participants, who all were seizure-free for at least 12 months after surgery. Our findings illustrated significant and unique desynchronization between EZ and the rest of the brain in the early to mid-seizure. We showed that aging and the duration of epilepsy intensify this desynchronization, which can be the outcome of abnormal neuroplasticity. Additionally, we illustrated that seizures evolve with various network topologies, confirming the existence of different epileptogenic networks in each patient. Our findings suggest not only the importance of early intervention in epilepsy but possible factors that correlate with disease severity. Moreover, by analyzing the propagation patterns of different seizures, we demonstrate the necessity of collecting sufficient data for identifying epileptogenic networks.

Cortical and subcortical morphological alteration in Angelman syndrome

BACKGROUND

Angelman syndrome (AS) is a neurodevelopmental disorder with serious seizures. We aim to explore the brain morphometry of patients with AS and figure out whether the seizure is associated with brain development.

METHODS

Seventy-three patients and 26 healthy controls (HC) underwent high-resolution structural brain MRI. Group differences between the HC group and the AS group and also between AS patients with seizure (AS-Se) and age-matched AS patients with non-seizure (AS-NSe) were compared. The voxel-based and surface-based morphometry analyses were used in our study. Gray matter volume, cortical thickness (CTH), and local gyrification index (LGI) were assessed to analyze the cortical and subcortical structure alteration in the AS brain.

RESULTS

Firstly, compared with the HC group, children with AS were found to have a significant decrease in gray matter volume in the subcortical nucleus, cortical, and cerebellum. However, the gray matter volume of AS patients in the inferior precuneus was significantly increased. Secondly, patients with AS had significantly increased LGI in the whole brain as compared with HC. Thirdly, the comparison of AS-Se and the AS-NSe groups revealed a significant decrease in caudate volume in the AS-Se group. Lastly, we further selected the caudate and the precuneus as ROIs for volumetric analysis, the AS group showed significantly increased LGI in the precuneus and reduced CTH in the right precuneus. Between the AS-Se and the AS-NSe groups, the AS-Se group exhibited significantly lower density in the caudate, while only the CTH in the left precuneus showed a significant difference.

CONCLUSIONS

These results revealed cortical and subcortical morphological alterations in patients with AS, including globally the decreased brain volume in the subcortical nucleus, the increased gray matter volume of precuneus, and the whole-brain increase of LGI and reduction of CTH. The abnormal brain pattern was more serious in patients with seizures, suggesting that the occurrence of seizures may be related to abnormal brain changes.

Intracranial direct electrical mapping reveals the functional architecture of the human basal ganglia

The basal ganglia play a key role in integrating a variety of human behaviors through the cortico–basal ganglia–thalamo–cortical loops. Accordingly, basal ganglia disturbances are implicated in a broad range of debilitating neuropsychiatric disorders. Despite accumulating knowledge of the basal ganglia functional organization, the neural substrates and circuitry subserving functions have not been directly mapped in humans. By direct electrical stimulation of distinct basal ganglia regions in 35 refractory epilepsy patients undergoing stereoelectroencephalography recordings, we here offer currently the most complete overview of basal ganglia functional characterization, extending not only to the expected sensorimotor responses, but also to vestibular sensations, autonomic responses, cognitive and multimodal effects. Specifically, some locations identified responses weren’t predicted by the model derived from large-scale meta-analyses. Our work may mark an important step toward understanding the functional architecture of the human basal ganglia and provide mechanistic explanations of non-motor symptoms in brain circuit disorders.

Direct electrical stimulation of the basal ganglia using implanted SEEG electrodes produced a variety of motor and non-motor effects in human participants, providing insight into the functional architecture of this key brain region.

Periodic electroencephalographic discharges and epileptic spasms involve cortico-striatal-thalamic loops on Arterial Spin Labeling Magnetic Resonance Imaging

Periodic discharges are a rare peculiar electroencephalogram pattern, occasionally associated with motor or other clinical manifestations, usually observed in critically ill patients. Their underlying pathophysiology remains poorly understood. Epileptic spasms in clusters and periodic discharges with motor manifestations share similar electroencephalogram pattern and some aetiologies of unfavourable prognosis such as subacute sclerosing panencephalitis or herpes encephalitis. Arterial spin labelling magnetic resonance imaging identifies localizing ictal and inter-ictal changes in neurovascular coupling, therefore assumed able to reveal concerned cerebral structures. Here, we retrospectively analysed ictal and inter-ictal arterial spin labelling magnetic resonance imaging in patients aged 6 months to 15 years (median 3 years 4 months) with periodic discharges including epileptic spasms, and compared these findings with those of patients with drug-resistant focal epilepsy who never presented periodic discharges nor epileptic spasms as well as to those of age-matched healthy controls. Ictal electroencephalogram was recorded either simultaneously with arterial spin labelling magnetic resonance imaging or during the close time lapse of patients' periodic discharges, whereas inter-ictal examinations were performed during the patients' active epilepsy but without seizures during the arterial spin labelling magnetic resonance imaging. Ictal arterial spin labelling magnetic resonance imaging was acquired in five patients with periodic discharges [subacute sclerosing panencephalitis (1), stroke-like events (3), West syndrome with cortical malformation (1), two of them also had inter-ictal arterial spin labelling magnetic resonance imaging]. Inter-ictal group included patients with drug-resistant epileptic spasms of various aetiologies (14) and structural drug-resistant focal epilepsy (8). Cortex, striatum and thalamus were segmented and divided in six functional subregions: prefrontal, motor (rostral, caudal), parietal, occipital and temporal. Rest cerebral blood flow values, absolute and relative to whole brain, were compared with those of age-matched controls for each subregion. Main findings were diffuse striatal as well as cortical motor cerebral blood flow increase during ictal examinations in generalized periodic discharges with motor manifestations (subacute sclerosing panencephalitis) and focal cerebral blood flow increase in corresponding cortical-striatal-thalamic subdivisions in lateralized periodic discharges with or without motor manifestations (stroke-like events and asymmetrical epileptic spasms) with straight topographical correlation with the electroencephalogram focus. For inter-ictal examinations, patients with epileptic spasms disclosed cerebral blood flow changes in corresponding cortical-striatal-thalamic subdivisions (absolute-cerebral blood flow decrease and relative-cerebral blood flow increase), more frequently when compared with the group of drug-resistant focal epilepsies, and not related to Vigabatrin treatment. Our results suggest that corresponding cortical-striatal-thalamic circuits are involved in periodic discharges with and without motor manifestations, including epileptic spasms, opening new insights in their pathophysiology and new therapeutical perspectives. Based on these findings, we propose a model for the generation of periodic discharges and of epileptic spasms combining existing pathophysiological models of cortical-striatal-thalamic network dynamics.

White matter alterations in focal to bilateral tonic-clonic seizures

We examined the white matter of patients with and without focal to bilateral tonic-clonic seizures (FBTCS), and control participants. A neural network based tract segmentation model (Tractseg) was used to isolate tract-specific, track-weighted tensor-based measurements from the tracts of interest. We compared the group differences in the track-weighted tensor-based measurements derived from whole and hemispheric tracts. We identified several regions that displayed significantly altered white matter in patients with focal epilepsy compared to controls. Furthermore, patients without FBTCS showed significantly increased white matter disruption in the inferior fronto-occipital fascicle and the striato-occipital tract. In contrast, the track-weighted tensor-based measurements from the FBTCS cohort exhibited a stronger resemblance to the healthy controls (compared to the non-FBTCS group). Our findings revealed marked alterations in a range of subcortical tracts considered critical in the genesis of seizures in focal epilepsy. Our novel application of tract-specific, track-weighted tensor-based measurements to a new clinical dataset aided the elucidation of specific tracts that may act as a predictive biomarker to distinguish patients likely to develop FBTCS.

Common ictal and interictal perfusion patterns. A window into the epileptogenic network and SUDEP mechanism in Drug Resistant Focal Epilepsy?

BACKGROUND

Focal epilepsies have been described as network disease. Noninvasive investigative techniques have been used to characterize epileptogenic networks.

OBJETIVE

To describe ictal and interictal cortical and subcortical perfusion patterns using single photon emission computed tomography (SPECT), in patients with drug-resistant epilepsy (DRE).

METHODS

Thirty-five interictal- ictal SPECT scans were obtained from 15 patients with DRE. A methodology was developed to get a relative perfusion index (PI) of 74 cortical and sub-cortical brain structures. K-means algorithm together with a modified v-fold cross-validation were used to identify the two regions of interest (ROI's) that represent hypoperfused and hyperperfused areas.

RESULTS

In common with the individual analysis, the statistical analysis evidenced that the hyperperfusion ROIs resulting from group analysis during interictal, and ictal involved mainly the cingulate gyrus, cuneus, the lingual gyrus, gyrus rectus as well as the putamen. ROIs hypoperfused included the red nucleus, the substantia nigra, and the medulla. The medians of the group analysis of the hypoperfusion and hyperperfusion ROIs were 0.601-0.565 and 1,133 - 1,119 for the ictal and interictal states, correspondingly. A group of mostly cortical structures involved in the hyperperfused ROIs in both interictal and ictal states showed no change or negative change in the transition from interictal to ictal state (mean change of -0.002). On the other hand, the brain stem, basal ganglia, red nucleus, and thalamus revealed a mean global change of 0.19, indicating a mild increase in the PI. However, some of these structures (red nucleus, substantia nigra, and medulla oblongata) remained hypoperfused during the interictal to ictal transition.

CONCLUSION

The methodology employed made it possible to identify common cortical and subcortical perfusion patterns not directly linked to epileptogenicity, but open a window for the epileptogenic network and sudden unexpected death (SUDEP) mechanism in DRE .

Anti-NMDAR encephalitis with bilateral basal ganglia MRI lesions at a distance of time: a case report

Background

Approximately half (55%) of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is known to show abnormal brain images, including high signal intensity in T2 or fluid attenuated inversion recovery (FLAIR) images. In a minority of anti-NMDAR encephalitis cases, high signal intensity on diffusion-weighted imaging (DWI) has been reported, a finding that is highly suggestive of a stroke.

Case presentation

We present the case of a 66-year-old man who experienced two separate focal seizure events, which involved first the right and then the left upper extremity in a short period of time. The patient showed focal clonic seizures involving right arm and hand, which sometimes evolved to bilateral tonic-clonic seizures on his first admission. Brain magnetic resonance imaging (MRI) showed high signal intensity on DWI and low signal intensity on the apparent diffusion coefficient (ADC) map of the left caudate nucleus and putamen. The patient was discharged symptom-free with anti-epileptic drugs for 2 weeks. The second admission occurred 4 days after the discharge. He exhibited a new symptom of focal clonic seizures involving left arm and hand while showing a brain lesion on the opposite side which is hyperintense on DWI image and hypointense on ADC map. The patient was eventually diagnosed with anti-NMDAR encephalitis according to the cerebrospinal fluid (CSF) antibody test.

Conclusions

This is the case of anti-NMDAR encephalitis patient whose DWI/ADC images revealed sequential involvement on the left and right basal ganglia with a short time interval. When stroke-like brain lesions on DWI are found in a patient with a focal seizure, a CSF study could help rule out autoimmune encephalitis. We also suggest that DWI/ADC map images may be useful for the early detection of anti-NMDAR encephalitis.

Fine motor impairment in children with epilepsy: Relations with seizure severity and lateralizing value

Motor skill deficits are common in epilepsy. The Grooved Pegboard Test (GPT) is the most commonly used fine motor task and is included in the NIH Common Data Elements Battery for the assessment of epilepsy. However, there are limited data on its utility in children and adolescents. The present study investigated the effectiveness of this task in children and adolescents with epilepsy clinically referred for neuropsychological evaluation in a tertiary medical center. Two hundred and two children and adolescents (ages 6-16, 104 males, 98 females) completed the GPT. Base rates of impairment were calculated, correlational analyses determined relations with clinical variables, and ANOVAs and t-tests assessed for differences by seizure type, gender, and lateralized deficits in those with lateralized focal epilepsy. The GPT was sensitive to fine motor impairment in these children and adolescents, with over 60% having impaired performances. Further, performance was significantly correlated with IQ, age of epilepsy onset, number of medications, and seizure frequency. At the group level, those with lateralized focal epilepsy did not show significant differences between left and right hands, though the GPT correctly lateralized 63% of those with large between-hand performance disparities (i.e., one standard deviation or greater). In sum, the GPT is sensitive to fine motor deficits in pediatric epilepsy and is related to known epilepsy severity factors. However, the ability of the task to lateralize epilepsy onset is not robust.

Frequency-Dependent Dynamics of Functional Connectivity Networks During Seizure Termination in Childhood Absence Epilepsy: A Magnetoencephalography Study

Objective: Our aim was to investigate the dynamics of functional connectivity (FC) networks during seizure termination in patients with childhood absence epilepsy (CAE) using magnetoencephalography (MEG) and graph theory (GT) analysis.

Methods: MEG data were recorded from 22 drug-naïve patients diagnosed with CAE. FC analysis was performed to evaluate the FC networks in seven frequency bands of the MEG data. GT analysis was used to assess the topological properties of FC networks in different frequency bands.

Results: The patterns of FC networks involving the frontal cortex were altered significantly during seizure termination compared with those during the ictal period. Changes in the topological parameters of FC networks were observed in specific frequency bands during seizure termination compared with those in the ictal period. In addition, the connectivity strength at 250–500 Hz during the ictal period was negatively correlated with seizure frequency.

Conclusions: FC networks associated with the frontal cortex were involved in the termination of absence seizures. The topological properties of FC networks in different frequency bands could be used as new biomarkers to characterize the dynamics of FC networks related to seizure termination.

Severe deficiency of the voltage-gated sodium channel NaV1.2 elevates neuronal excitability in adult mice

Scn2a encodes the voltage-gated sodium channel NaV1.2, a main mediator of neuronal action potential firing. The current paradigm suggests that NaV1.2 gain-of-function variants enhance neuronal excitability, resulting in epilepsy, whereas NaV1.2 deficiency impairs neuronal excitability, contributing to autism. However, this paradigm does not explain why ∼20%-30% of individuals with NaV1.2 deficiency still develop seizures. Here, we report the counterintuitive finding that severe NaV1.2 deficiency results in increased neuronal excitability. Using a NaV1.2-deficient mouse model, we show enhanced intrinsic excitability of principal neurons in the prefrontal cortex and striatum, brain regions known to be involved in Scn2a-related seizures. This increased excitability is autonomous and reversible by genetic restoration of Scn2a expression in adult mice. RNA sequencing reveals downregulation of multiple potassium channels, including KV1.1. Correspondingly, KV channel openers alleviate the hyperexcitability of NaV1.2-deficient neurons. This unexpected neuronal hyperexcitability may serve as a cellular basis underlying NaV1.2 deficiency-related seizures.

On seizure semiology

The clinical expression of seizures represents the main symptomatic burden of epilepsy. Neural mechanisms of semiologic production in epilepsy, especially for complex behaviors, remain poorly known. In a framework of epilepsy as a network rather than as a focal disorder, we can think of semiology as being dynamically produced by a set of interconnected structures, in which specific rhythmic interactions, and not just anatomical localization, are likely to play an important part in clinical expression. This requires a paradigm shift in how we think about seizure organization, including from a presurgical evaluation perspective. Semiology is a key data source, albeit with significant methodological challenges for its use in research, including observer bias and choice of semiologic categories. Better understanding of semiologic categorization and pathophysiological correlates is relevant to seizure classification systems. Advances in knowledge of neural mechanisms as well as anatomic correlates of different semiologic patterns could help improve knowledge of epilepsy networks and potentially contribute to therapeutic innovations.

Activation of the basal ganglia and indirect pathway neurons during frontal lobe seizures

There are no detailed descriptions of neuronal circuit active during frontal lobe motor seizures. Using activity reporter mice, local field potential recordings, tissue clearing, viral tracing, and super-resolution microscopy, we found neuronal activation after focal motor to bilateral tonic-clonic seizures in the striatum, globus pallidus externus, subthalamic nucleus, substantia nigra pars reticulata and neurons of the indirect pathway. Seizures preferentially activated dopamine D2 receptor-expressing neurons over D1 in the striatum, which have different projections. Furthermore, the D2 receptor agonist infused into the striatum exerted an anticonvulsant effect. Seizures activate structures via short and long latency loops, and anatomical connections of the seizure focus determine the seizure circuit. These studies, for the first time, show activation of neurons in the striatum, globus pallidus, subthalamic nucleus, and substantia nigra during frontal lobe motor seizures on the cellular level, revealing a complex neuronal activation circuit subject to modulation by the basal ganglia.

Pain behavior without pain sensation: an epileptic syndrome of "symbolism for pain"?

"Asymbolia for pain" has shown the potentiality of diseased insular networks to dissociate sensory from affective-behavioral dimensions of pain, resulting in the lack of appropriate motor and affective responses despite preserved sensory aspect of pain. Here, we describe 4 patients with an inverse phenomenon of asymbolia for pain, namely an isolated "symbolism for pain" triggered by epileptic seizures, characterized by pain behavior without declarative pain sensation despite fully preserved contact and vigilance. Stereoelectroencephalography demonstrated in each case focal seizure discharges within the posterior insulo-opercular cortex, with little or no propagation to other cortical structures, especially those considered to drive subjective pain experiences. The pain behavior might reflect seizure propagation from the insula to brain networks serving for behavioral responses associated with pain, including the cingulate motor region and possibly also the basal ganglia. We propose that the isolated symbolism for pain is a novel epileptic syndrome of dissociation between pain perception and behaviors associated with the insular nociceptive-related networks.

Bypassing the Blood-Brain Barrier: Direct Intracranial Drug Delivery in Epilepsies

Epilepsies are common chronic neurological diseases characterized by recurrent unprovoked seizures of central origin. The mainstay of treatment involves symptomatic suppression of seizures with systemically applied antiseizure drugs (ASDs). Systemic pharmacotherapies for epilepsies are facing two main challenges. First, adverse effects from (often life-long) systemic drug treatment are common, and second, about one-third of patients with epilepsy have seizures refractory to systemic pharmacotherapy. Especially the drug resistance in epilepsies remains an unmet clinical need despite the recent introduction of new ASDs. Apart from other hypotheses, epilepsy-induced alterations of the blood-brain barrier (BBB) are thought to prevent ASDs from entering the brain parenchyma in necessary amounts, thereby being involved in causing drug-resistant epilepsy. Although an invasive procedure, bypassing the BBB by targeted intracranial drug delivery is an attractive approach to circumvent BBB-associated drug resistance mechanisms and to lower the risk of systemic and neurologic adverse effects. Additionally, it offers the possibility of reaching higher local drug concentrations in appropriate target regions while minimizing them in other brain or peripheral areas, as well as using otherwise toxic drugs not suitable for systemic administration. In our review, we give an overview of experimental and clinical studies conducted on direct intracranial drug delivery in epilepsies. We also discuss challenges associated with intracranial pharmacotherapy for epilepsies.

The Ictal Signature of Thalamus and Basal Ganglia in Focal Epilepsy: A SEEG Study

OBJECTIVE

To determine the involvement of subcortical regions in human epilepsy by analyzing direct recordings from these regions during epileptic seizures using stereo-EEG (SEEG).

METHODS

We studied the SEEG recordings of a large series of patients (74 patients, 157 seizures) with an electrode sampling the thalamus and in some cases also the basal ganglia (caudate nucleus, 22 patients; and putamen, 4 patients). We applied visual analysis and signal quantification methods (Epileptogenicity Index [EI]) to their ictal recordings and compared electrophysiologic with clinical data.

RESULTS

We found that in 86% of patients, thalamus was involved during seizures (visual analysis) and 20% showed high values of epileptogenicity (EI >0.3). Basal ganglia may also disclose high values of epileptogenicity (9% in caudate nucleus) but to a lesser degree than thalamus (p < 0.01). We observed different seizure onset patterns including low voltage high frequency activities. We found high values of thalamic epileptogenicity in different epilepsy localizations, including opercular and motor epilepsies. We found no difference between epilepsy etiologies (cryptogenic vs malformation of cortical development, p = 0.77). Thalamic epileptogenicity was correlated with the extension of epileptogenic networks (p = 0.02, ρ 0.32). We found a significant effect (p < 0.05) of thalamic epileptogenicity regarding the postsurgical outcome (higher thalamic EI corresponding to higher probability of surgical failure).

CONCLUSIONS

Thalamic involvement during seizures is common in different seizure types. The degree of thalamic epileptogenicity is a possible marker of the epileptogenic network extension and of postsurgical prognosis.

Disrupted basal ganglia-thalamocortical loops in focal to bilateral tonic-clonic seizures

Focal to bilateral tonic-clonic seizures are associated with lower quality of life, higher risk of seizure-related injuries, increased chance of sudden unexpected death, and unfavourable treatment outcomes. Achieving greater understanding of their underlying circuitry offers better opportunity to control these seizures. Towards this goal, we provide a network science perspective of the interactive pathways among basal ganglia, thalamus and cortex, to explore the imprinting of secondary seizure generalization on the mesoscale brain network in temporal lobe epilepsy. Specifically, we parameterized the functional organization of both the thalamocortical network and the basal ganglia-thalamus network with resting state functional MRI in three groups of patients with different focal to bilateral tonic-clonic seizure histories. Using the participation coefficient to describe the pattern of thalamocortical connections among different cortical networks, we showed that, compared to patients with no previous history, those with positive histories of focal to bilateral tonic-clonic seizures, including both remote (none for >1 year) and current (within the past year) histories, presented more uniform distribution patterns of thalamocortical connections in the ipsilateral medial-dorsal thalamic nuclei. As a sign of greater thalamus-mediated cortico-cortical communication, this result comports with greater susceptibility to secondary seizure generalization from the epileptogenic temporal lobe to broader brain networks in these patients. Using interregional integration to characterize the functional interaction between basal ganglia and thalamus, we demonstrated that patients with current history presented increased interaction between putamen and globus pallidus internus, and decreased interaction between the latter and the thalamus, compared to the other two patient groups. Importantly, through a series of 'disconnection' simulations, we showed that these changes in interactive profiles of the basal ganglia-thalamus network in the current history group mainly depended upon the direct but not the indirect basal ganglia pathway. It is intuitively plausible that such disruption in the striatum-modulated tonic inhibition of the thalamus from the globus pallidus internus could lead to an under-suppressed thalamus, which in turn may account for their greater vulnerability to secondary seizure generalization. Collectively, these findings suggest that the broken balance between basal ganglia inhibition and thalamus synchronization can inform the presence and effective control of focal to bilateral tonic-clonic seizures. The mechanistic underpinnings we uncover may shed light on the development of new treatment strategies for patients with temporal lobe epilepsy.

Distinguishing Dependent-Stage Secondary Epileptogenesis in a Complex Case of Giant Hypothalamic Hamartoma With Assistance of a Computational Method

Besides gelastic seizures, hypothalamic hamartoma (HH) is also noted for its susceptibility to remote secondary epileptogenesis. Although clinical observations have demonstrated its existence, and a three-stage theory has been proposed, how to determine whether a remote symptom is spontaneous or dependent on epileptic activities of HH is difficult in some cases. Herein, we report a case of new non-gelastic seizures in a 9-year-old female associated with a postoperatively remaining HH. Electrophysiological examinations and stereo-electroencephalography (SEEG) demonstrated seizure onsets with slow-wave and fast activities on the outside of the HH. By using computational methodologies to calculate the network dynamic effective connectivities, the importance of HH in the epileptic network was revealed. After SEEG-guided thermal coagulation of the remaining HH, the patient finally was seizure-free at the 2-year follow-up. This case showed the ability of computational methods to reveal information underlying complex SEEG signals, and further demonstrated the dependent-stage secondary epileptogenesis, which has been rarely reported.

When the Brakes Fail: Basal Ganglia and Seizure Generalization

Disrupted Basal Ganglia–Thalamocortical Loops in Focal to Bilateral Tonic-Clonic Seizures

He X, Chaitanya G, Asma B, et al. Brain. 2020;143(1):175-190. doi:10.1093/brain/awz361.

Focal to bilateral tonic-clonic seizures are associated with lower quality of life, higher risk of seizure-related injuries, increased chance of sudden unexpected death, and unfavorable treatment outcomes. Achieving greater understanding of their underlying circuitry offers better opportunity to control these seizures. Toward this goal, we provide a network science perspective of the interactive pathways among basal ganglia, thalamus and cortex, to explore the imprinting of secondary seizure generalization on the mesoscale brain network in temporal lobe epilepsy. Specifically, we parameterized the functional organization of both the thalamocortical network and the basal ganglia–thalamus network with resting state functional magnetic resonance imaging in 3 groups of patients with different focal to bilateral tonic-clonic seizure histories. Using the participation coefficient to describe the pattern of thalamocortical connections among different cortical networks, we showed that, compared to patients with no previous history, those with positive histories of focal to bilateral tonic-clonic seizures, including both remote (none for >1 year) and current (within the past year) histories, presented more uniform distribution patterns of thalamocortical connections in the ipsilateral medial-dorsal thalamic nuclei. As a sign of greater thalamus-mediated cortico-cortical communication, this result comports with greater susceptibility to secondary seizure generalization from the epileptogenic temporal lobe to broader brain networks in these patients. Using interregional integration to characterize the functional interaction between basal ganglia and thalamus, we demonstrated that patients with current history presented increased interaction between putamen and globus pallidus internus, and decreased interaction between the latter and the thalamus, compared to the other 2 patient groups. Importantly, through a series of “disconnection” simulations, we showed that these changes in interactive profiles of the basal ganglia–thalamus network in the current history group mainly depended upon the direct but not the indirect basal ganglia pathway. It is intuitively plausible that such disruption in the striatum-modulated tonic inhibition of the thalamus from the globus pallidus internus could lead to an under-suppressed thalamus, which in turn may account for their greater vulnerability to secondary seizure generalization. Collectively, these findings suggest that the broken balance between basal ganglia inhibition and thalamus synchronization can inform the presence and effective control of focal to bilateral tonic-clonic seizures. The mechanistic underpinnings we uncover may shed light on the development of new treatment strategies for patients with temporal lobe epilepsy.

Multiple Oscillatory Push-Pull Antagonisms Constrain Seizure Propagation

OBJECTIVE

Drug-resistant focal epilepsy is widely recognized as a network disease in which epileptic seizure propagation is likely coordinated by different neuronal oscillations such as low-frequency activity (LFA), high-frequency activity (HFA), or low-to-high cross-frequency coupling. However, the mechanism by which different oscillatory networks constrain the propagation of focal seizures remains unclear.

METHODS

We studied focal epilepsy patients with invasive electrocorticography (ECoG) recordings and compared multilayer directional network interactions between focal seizures either with or without secondary generalization. Within-frequency and cross-frequency directional connectivity were estimated by an adaptive directed transfer function and cross-frequency directionality, respectively.

RESULTS

In the within-frequency epileptic network, we found that the seizure onset zone (SOZ) always sent stronger information flow to the surrounding regions, and secondary generalization was accompanied by weaker information flow in the LFA from the surrounding regions to SOZ. In the cross-frequency epileptic network, secondary generalization was associated with either decreased information flow from surrounding regions' HFA to SOZ's LFA or increased information flow from SOZ's LFA to surrounding regions' HFA.

INTERPRETATION

Our results suggest that the secondary generalization of focal seizures is regulated by numerous within- and cross-frequency push-pull dynamics, potentially reflecting impaired excitation-inhibition interactions of the epileptic network. ANN NEUROL 2019;86:683-694.