The detection of absence seizures using cross-frequency coupling analysis with a deep learning network

High frequency oscillations are important novel biomarkers of epileptogenic tissue. The interaction of oscillations across different time scales is revealed as cross-frequency coupling (CFC) representing a high-order structure in the functional organization of brain rhythms. New artificial intelligence methods such as deep learning neural networks can provide powerful tools for automated analysis of EEG. Here we present a Stacked Sparse Autoencoder (SSAE) trained to recognize absence seizure activity based on the cross-frequency patterns within scalp EEG. We used EEG records from the Temple University Hospital database. Absence seizures (n = 94) from 12 patients were taken into analysis along with segments of background activity. Half of the records were selected randomly for network training and the second half were used for testing. Power-to-power coupling was calculated between all frequencies 2-120 Hz pairwise using the EEGLAB toolbox. The resulting CFC matrices were used as training or testing inputs to the autoencoder. The trained network was able to recognize background and seizure segments (not used in training) with a sensitivity of 96.3%, specificity of 99.8% and overall accuracy of 98.5%. Our results provide evidence that the SSAE neural networks can be used for automated detection of absence seizures within scalp EEG.

Spike and wave discharges detection in genetic absence epilepsy rat from Strasbourg and patients with genetic generalized epilepsy

OBJECTIVE

Generalised spike and wave discharges (SWDs) are pathognomonic EEG signatures for diagnosing absence seizures in patients with Genetic Generalized Epilepsy (GGE). The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is one of the best-validated animal models of GGE with absence seizures.

METHODS

We developed an SWDs detector for both GAERS rodents and GGE patients with absence seizures using a neural network method. We included 192 24-hour EEG sessions recorded from 18 GAERS rats, and 24-hour scalp-EEG data collected from 11 GGE patients.

RESULTS

The SWDs detection performance on GAERS showed a sensitivity of 98.01% and a false positive (FP) rate of 0.96/hour. The performance on GGE patients showed 100% sensitivity in five patients, while the remaining patients obtained over 98.9% sensitivity. Moderate FP rates were seen in our patients with 2.21/hour average FP. The detector trained within our patient cohort was validated in an independent dataset, TUH EEG Seizure Corpus (TUSZ), that showed 100% sensitivity in 11 of 12 patients and 0.56/hour averaged FP.

CONCLUSIONS

We developed a robust SWDs detector that showed high sensitivity and specificity for both GAERS rats and GGE patients.

SIGNIFICANCE

This detector can assist researchers and neurologists with the time-efficient and accurate quantification of SWDs.

Frequency of non-generalized tonic clonic seizures in a referral population of dogs

Absence seizures are a type of generalized onset seizure associated in humans with brief activity interruptions, unresponsiveness and staring. Absence seizures are infrequently reported in veterinary patients, visually indistinguishable from focal seizures, and so may be grouped as non-generalized tonic clonic seizures (non-GTCS). The objective of this retrospective study was to provide a preliminary understanding of the frequency of non-GTCS in dogs and estimate its prevalence by evaluating the distribution of seizure types presented to a referral hospital over 4 years (May 2017-April 2021), as determined from the medical record history and electroencephalography (EEG) diagnostic testing where available. A total of 528 cases were included via a medical record search for dogs with epilepsy and/or seizures presented to the neurology or emergency services. Cases were categorized into seizure types based on reported clinical signs. Each year, 53-63 % of seizure cases were described as generalized tonic clonic seizures (GTCS), 9-15 % GTCS with additional events and 29-35 % suspected non-GTCS. EEG confirmed absence seizures in 12 of 44 EEGs, 5 cases having a history of GTCS and seven without prior GTCS. This preliminary study suggests that non-GTCS may be relatively common as one third of seizure cases in the referral population presented with non-GTCS clinical signs. Prospective studies using EEG are merited to definitively determine the prevalence of these different seizure types in dogs. Acknowledging the impact of these seizures will improve awareness, aiding veterinarians in their recognition, diagnosis and potential treatment options.

Paroxysmal slow-wave discharges in a model of absence seizure are coupled to gamma oscillations in the thalamocortical and limbic systems

OBJECTIVE

Using the gamma-butyrolactone (GBL) model of absence seizures in Long-Evans rats, this study investigated if gamma (30-160 Hz) activity were cross-frequency modulated by the 2-6 Hz slow-wave discharges induced by GBL in the limbic system. We hypothesized that inactivation of the nucleus reuniens (RE), which projects to frontal cortex (FC) and hippocampus, would affect the cross-frequency coupling of gamma (γ) in different brain regions.

METHODS

Local field potentials were recorded by electrodes implanted in the FC, ventrolateral thalamus (TH), basolateral amygdala (BLA), nucleus accumbens (NAC), and dorsal hippocampus (CA1) of behaving rats. At each electrode, the coupling between the γ amplitude envelope to the phase of the 2-6 Hz slow-waves (SW) was measured by modulation index (MI) or cross-frequency coherence (CFC) of γ amplitude with SW. In separate experiments, the RE was infused with saline or GABA_A receptor agonist, muscimol, before the injection of GBL.

RESULTS

Following GBL injection, an increase in MI and CFC of SW to γ1 (30-58 Hz), γ2 (62-100 Hz) and γ3 (100-160 Hz) bands was observed at the FC, hippocampus and BLA, with significant increase in SW-γ1 and SW-γ3 coupling at TH, and increase in peak SW-γ1 CFC at NAC. Strong SW-γ modulation was also found during baseline immobility high-voltage spindles. Muscimol inactivation of RE, as compared to saline infusion, significantly decreased SW-γ1 CFC in the FC, and peak frequency of the SW-γ1 CFC in the thalamus, but did not significantly alter SW-γ CFCs in the hippocampus, BLA or NAC.

SIGNIFICANCE

The paroxysmal 2-6 Hz SW discharges, a hallmark of absence seizure, significantly modulate γ activity in the hippocampus, BLA and NAC, suggesting a modulation of limbic functions. RE inactivation disrupted the SW modulation of FC and TH, partly supporting our hypothesis that RE participates in the modulation of SW discharges.

Deletion of Phospholipase C β1 in the Thalamic Reticular Nucleus Induces Absence Seizures

Absence seizures are caused by abnormal synchronized oscillations in the thalamocortical (TC) circuit, which result in widespread spike-and-wave discharges (SWDs) on electroencephalography (EEG) as well as impairment of consciousness. Thalamic reticular nucleus (TRN) and TC neurons are known to interact dynamically to generate TC circuitry oscillations during SWDs. Clinical studies have suggested the association of Plcβ1 with early-onset epilepsy, including absence seizures. However, the brain regions and circuit mechanisms related to the generation of absence seizures with Plcβ1 deficiency are unknown. In this study, we found that loss of Plcβ1 in mice caused spontaneous complex-type seizures, including convulsive and absence seizures. Importantly, TRN-specific deletion of Plcβ1 led to the development of only spontaneous SWDs, and no other types of seizures were observed. Ex vivo slice patch recording demonstrated that the number of spikes, an intrinsic TRN neuronal property, was significantly reduced in both tonic and burst firing modes in the absence of Plcβ1. We conclude that the loss of Plcβ1 in the TRN leads to decreased excitability and impairs normal inhibitory neuronal function, thereby disrupting feedforward inhibition of the TC circuitry, which is sufficient to cause hypersynchrony of the TC system and eventually leads to spontaneous absence seizures. Our study not only provides a novel mechanism for the induction of SWDs in Plcβ1-deficient patients but also offers guidance for the development of diagnostic and therapeutic tools for absence epilepsy.

Sleep disorders and ADHD symptoms in children and adolescents with typical absence seizures: An observational study

OBJECTIVE

To assess the occurrence of sleep disorders (SD) and attention deficit hyperactivity disorder (ADHD) symptoms in children with typical absence seizures (TAS) compared to control children and to evaluate the impact of epilepsy-related factors on sleep and attention in children with TAS.

METHODS

The Sleep Disturbance Scale for Children (SDSC) and the ADHD rating scale were filled in by parents of a cohort composed by 82 children aged from 5 to 15.6 years, 49% of boys (41 with TAS with a syndromic diagnosis of childhood absence epilepsy and 41 controls). For children with TAS, the Pediatric Epilepsy Side Effects Questionnaire was completed. Statistical analyses were conducted in order to compare sleep and attention scores between groups. In children with TAS, a correlation was computed between these scores. Logistics regression models were conducted to identify predictors of excessive diurnal sleepiness and inattention in children with TAS.

RESULTS

Compared to controls, children with TAS had higher total scores for subjective sleep (mean 42.9 vs 38.3, p = 0.05) and attention disorders (mean 16.8 vs 11.6, p = 0.01), especially for excessive diurnal sleepiness (mean 3.9 vs 3.2, p = 0.02) and inattention (mean 9.3 vs 5.6, p = 0.003) components. In children with TAS, sleep problems were significantly under-reported by parents. Sleep disorders symptoms as breathing-related sleep disturbance, excessive diurnal sleepiness or naps at or after 7 years of age were reported. Subjective sleep and attention disorders were significantly correlated (r = 0.43, p = 0.01). Subjective excessive diurnal sleepiness may be the result of a polytherapy (p = 0.05) or a side effect of anti-seizure medication (ASM) (p = 0.03) but children without medication side effects also reported subjective SD. In children with TAS, the risk of inattention symptoms was increased in boys (p = 0.02), with a high BMI (p = 0.05), or with ASM side effects (p = 0.03).

CONCLUSIONS

This study demonstrates that children with TAS are at risk of sleep and attention disorder symptoms. If attention disorders in a context of epilepsy are now widely assessed and identified, sleep disorders are still under-estimated. An accurate identification and management of sleep disorders could improve academic performances, quality of life, and seizure management in children with TAS.

Dazed and Confused: Altered Mental Status in an Adolescent Male

BACKGROUND

Absence status epilepticus (ASE) is a form of generalized nonconvulsive status epilepticus. ASE is characterized by impairment in consciousness, which can vary widely, making the diagnosis more difficult. The typical patient with ASE will be confused yet responsive and in a "trance-like state" with delayed speech, clumsy gait, and the ability to perform simple tasks after prompting. With treatment, typical ASE has an excellent prognosis and does not appear to be associated with significant neuronal damage.

CASE PRESENTATION

An 11-year-old boy with history of febrile seizures presented to the emergency department (ED) with altered mental status without trauma or ingestion. His vital signs and physical examination were normal, with the exception of appearing intoxicated with sparse verbalization and inappropriate emotional responses. All laboratory results and imaging were unremarkable. While in the ED, his neurologic examination trended toward normal, returning almost to baseline. He was admitted to the hospital for video electroencephalogram, which revealed status epilepticus. After benzodiazepine therapy, epileptic electrical activity ceased and the patient's symptoms resolved. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: ASE is a rare condition that is uncommonly described in the pediatric population. These patients are frequently misdiagnosed on initial presentation as their alteration in mental status can be easily confused with ingestion, trauma, psychiatric illness, or infectious etiologies. Overturning the long-standing emergency dogma of "if they're talking to you, it's not a seizure" is undoubtedly difficult, but both pediatric and adult providers should be aware of this clinical entity.

CACNA1A-associated epilepsy: Electroclinical findings and treatment response on seizures in 18 patients

CACNA1A pathogenic mutations are involved in various neurological phenotypes including episodic ataxia (EA2), spinocerebellar ataxia (SCA6), and familial hemiplegic migraine (FHM1). Epilepsy is poorly documented. We studied 18 patients (10 males) carrying de novo or inherited CACNA1A mutations, with median age of 2,5 years at epilepsy onset. Eight mutations were novel. Two variants known leading to gain of function (GOF) were found in 5 patients. Five other patients had non-sense variants leading to loss of function (LOF). Seizures were most often revealed by either status epilepticus (SE) (n = 8), eventually triggered by fever (n = 5), or absences/behavioural arrests (n = 7). Non-epileptic paroxysmal events were frequent and consisted in recurrent hemiplegic accesses (n = 9), jitteriness in the neonatal period (n = 6), and ocular paroxysmal events (n = 9). Most of the patients had early permanent cerebellar dysfunction (n = 16) and early moderate to severe global developmental delay (GDD)/intellectual deficiency (ID) (n = 17). MRI was often abnormal, with cerebellar (n = 8) and/or cerebral (n = 6) atrophy. Stroke-like occurred in 2 cases. Some antiepileptic drugs including topiramate, levetiracetam, lamotrigine and valproate were effective on seizures. Acetazolamide and calcium channel blockers were often effective when used. More than half of the patients had refractory epilepsy. CACNA1A mutation should be evoked in front of 2 main electro-clinical phenotypes that are associated with permanent cerebellar dysfunction and moderate to severe GDD/ID. The first one, found in all 5 patients with GOF variants, is characterized by intractable seizures, early and recurrent SE and hemiplegic accesses. The second, less severe, found in 5 patients with LOF variants, is characterized by refractory early onset absence seizures.

The effect of external voltage stimulation on absence seizures

BACKGROUND:

Absence epilepsy (AE) is a systemic disease of the brain, which mainly occurs during childhood and adolescence. The control mechanism is still unclear, and few theoretical studies have been conducted to investigate this.

OBJECTIVE:

In this paper, we employed external direct voltage stimulation in the subthalamic nucleus to explore mechanisms that inhibit absence seizures.

METHODS:

All simulation results are obtained by the four-order Runge-Kutta method in the MATLAB environment. The inhibition mechanism can be inferred from the results.

RESULTS:

We found that the seizures may be inhibited by tuning the strength of the voltage to suitable ranges. This regulation may be achieved through the competition between the inhibitory projections from the basal ganglia to the thalamus.

CONCLUSION:

Because the mechanism underlying the treatment of epilepsy with a uniform direct current electric field is unclear, we hope that these results can inspire further experimental studies.

Scn1a and Cacna1a mutations mutually alter their original phenotypes in rats

This study aimed to examine the effects of Cacna1a mutation on the phenotype of Scn1a-associated epilepsy in rats. We used rats with an N1417H missense mutation in the Scn1a gene and others with an M251K mutation in the Cacna1a gene. Scn1a/Cacna1a double mutant rats were generated by mating both Scn1a and Cacna1a mutants. We investigated general health and the epileptic phenotype in all these genotypes. The onset threshold of hyperthermia-induced seizures was examined at 5 weeks and spontaneous seizures were monitored using video-EEG recordings from 6 to 12 weeks of age. Scn1a/Cacna1a double mutants showed significantly reduced threshold for hyperthermia-sensitive seizures onset compared with the Scn1a mutants and had absence seizures having 6-7 c/s spike-wave bursts with changes in the spike-wave pattern, whereas Cacna1a mutants had regular 6-7 c/s spike-wave bursts. In Scn1a/Cacna1a double mutants, 6-7 c/s spike-wave bursts were accompanied with eyelid myoclonia and continuously shifting generalized clonic seizures, which were not observed in either Scn1a or Cacna1a mutants. Although a curvature of the spine was observed in rats of all these genotypes, the degree of curvature was more pronounced in Scn1a/Cacna1a double mutants, followed by Cacna1a and Scn1a mutants. Our results indicate that Cacna1a and Scn1a mutations mutually alter their original phenotypes in rats. The phenotype of absence seizures with eyelid myoclonia, generalized clonic seizures, and of spine curvature in the Scn1a/Cacna1a double mutants were similar to that observed in patients with Dravet syndrome.

Polyspike ictal-onset absence seizures in a pediatric patient with Down syndrome

Polyspike ictal-onset absence seizure has been reported in adult patients with genetic generalized epilepsy but is a novel pattern in the pediatric population. Absence seizures are usually associated with generalized spike-and-wave on EEG. However, we present the case of a 10-year-old girl with Down syndrome and developmental delays who presented with atypical absence seizure associated with an unusual electroencephalographic (EEG) pattern of polyspike ictal-onset. Recognition of this ictal pattern in the pediatric population, as previously reported in adult populations, is important as it can have therapeutic and prognostic implications.

•

Absence seizures are usually associated with generalized spike and wave, but here we report a polyspike ictal-onset pattern.

•

The pattern appeared as purely a polyspike ictal-onset, or polyspikes intermixed or preceding the generalized spike and wave.

•

Polyspike ictal onset is differentiated from generalized paroxysmal fast activity (GPFA), by morphology & other features.

Distinct Topographical Patterns of Spike-Wave Discharge in Transgenic and Pharmacologically Induced Absence Seizure Models

Absence seizures (AS) are generalized non-convulsive seizures characterized by a brief loss of consciousness and spike-and-wave discharges (SWD) in an electroencephalogram (EEG). A number of animal models have been developed to explain the mechanisms of AS, and thalamo-cortical networks are considered to be involved. However, the cortical foci have not been well described in mouse models of AS. This study aims to use a high density EEG in pathophysiologically different AS models to compare the spatiotemporal patterns of SWDs. We used two AS models: a pharmacologically induced model (gamma-hydroxybutyric acid, GHB model) and a transgenic model (phospholipase beta4 knock-out, PLCβ4 model). The occurrences of SWDs were confirmed by thalamic recordings. The topographical analysis of SWDs showed that the onset and propagation patterns were markedly distinguishable between the two models. In the PLCβ4 model, the foci were located within the somatosensory cortex followed by propagation to the frontal cortex, whereas in the GHB model, a majority of SWDs was initiated in the prefrontal cortex followed by propagation to the posterior cortex. In addition, in the GHB model, foci were also observed in other cortical areas. This observation indicates that different cortical networks are involved in the generation of SWDs across the two models.

Lacosamide for uncontrolled primary generalized tonic-clonic seizures: An open-label pilot study with 59-week extension

OBJECTIVE

Assess the safety of adjunctive lacosamide for the treatment of uncontrolled primary generalized tonic-clonic seizures in patients (16-65 years) with primary generalized (genetic) epilepsy (PGE).

METHODS

An open-label pilot safety study (SP0961; NCT01118949), comprising 12 weeks' historical baseline, 4 weeks' prospective baseline, 3 weeks' titration (target: 400mg/day adjunctive lacosamide) and 6 weeks' maintenance. Patients who continued to the extension study (SP0962; NCT01118962) then received ≤59 weeks of flexible treatment (100-800mg/day lacosamide with flexible dosing of concomitant antiepileptic drugs). The primary outcomes for SP0961 were the mean change (±standard deviation) in absence seizure or myoclonic seizure days per 28days from prospective baseline to maintenance; for SP0962, the incidence of treatment-emergent adverse events (TEAEs) and withdrawals because of TEAEs.

RESULTS

Of the 49 patients who enrolled, 40 (82%) completed the pilot study and 9 discontinued (5 because of adverse events). Of the 39 patients who continued to the extension study, 10 discontinued (2 owing to TEAEs) and 29 (74%) completed the study. During the pilot study, patients reported a reduction in mean (±standard deviation) absence and myoclonic seizure days per 28days (-0.37±4.80, -2.19±5.80). Reductions were also observed during the extension study (-2.38±5.54, -2.78±6.43). Five patients in SP0961 and 2 patients in SP0962 experienced TEAEs of new or increased frequency of absence seizures or myoclonic seizures. The most common TEAEs during SP0961 were dizziness (39%) and nausea (27%), and during SP0962 were dizziness (26%) and upper respiratory tract infection (26%).

CONCLUSIONS

The safety profile of adjunctive lacosamide was similar to that previously published. Adjunctive lacosamide did not systematically worsen absence or myoclonic seizures, and appears to be well tolerated in patients with PGE.

Brain correlates of spike and wave discharges in GLUT1 deficiency syndrome

Purpose

To provide imaging biomarkers of generalized spike-and-wave discharges (GSWD) in patients with GLUT1 deficiency syndrome (GLUT1DS).

Methods

Eighteen GLUT1DS patients with pathogenetic mutation in SLC2A1 gene were studied by means of Video-EEG simultaneously recorded with functional MRI (VideoEEG-fMRI). A control group of sex and age-matched patients affected by Genetic Generalized Epilepsy (GGE) with GSWD were investigated with the same protocol. Within and between groups comparison was performed as appropriated. For GLUT1DS, correlations analyses between the contrast of interest and the main clinical measurements were provided.

Results

EEG during fMRI revealed interictal GSWD in 10 GLUT1DS patients. Group-level analysis showed BOLD signal increases at the premotor cortex and putamen. With respect to GGE, GLUT1DS patients demonstrated increased neuronal activity in the putamen, precuneus, cingulate cortex, SMA and paracentral lobule. Whole-brain correlation analyses disclosed a linear relationship between the GSWD-related BOLD changes and the levels of glycorrhachia at diagnosis over the sensory-motor cortex and superior parietal lobuli.

Conclusion

The BOLD dynamics related to GSWD in GLUT1DS are substantially different from typical GGE showing the former an increased activity in the premotor-striatal network and a decrease in the thalamus. The revealed hemodynamic maps might represent imaging biomarkers of GLUT1DS, being potentially useful for a precocious diagnosis of this genetic disorder.

•

First report describing the epilepsy-related hemodynamic patterns in GLUT1DS.

•

The revealed BOLD maps can represent GLUT1DS imaging biomarkers.

•

The premotor-striatal network generates the GSWD in GLUT1DS.

•

The glycorrhachia at diagnosis influences the epilepsy-related BOLD maps.

Dynamics of sensorimotor cortex activation during absence and myoclonic seizures in a mouse model of juvenile myoclonic epilepsy

OBJECTIVE

Generalized epilepsy syndromes often confer multiple types of seizures, but it is not known if these seizures activate separate or overlapping brain networks. Recently, we reported that mice with a juvenile myoclonic epilepsy mutation (Gabra1[A322D]) exhibited both absence and myoclonic generalized seizures. Here, we determined the time course of sensorimotor cortex activation and the spatial distribution of spike voltage during these two seizures.

METHODS

We implanted Gabra1^+/A322D mice with multiple electroencephalography (EEG) electrodes over bilateral somatosensory cortex barrel fields (S1) and anterior (aM1) and posterior (pM1) motor cortices and recorded absence seizures/spike-wave discharges (SWDs) and myoclonic seizures. We used nonlinear-association analyses and cross-correlation calculations to determine the strength, leading regions, and time delays of cortical coupling from the preictal to ictal states and within the spike and interspike periods. The distribution of spike voltage was also measured in SWDs and myoclonic seizures.

RESULTS

EEG connectivity among all electrode pairs increased at the onset of both SWDs and myoclonic seizures. Surprisingly, during spikes of both seizure types, S1 led M1 with similar delay times. Myoclonic seizure spikes started more focally than SWD spikes, with a significant majority appearing first only in S1 electrodes, whereas a substantial fraction of SWD spikes were detected first in S1 and at least one M1 electrode. The absolute voltage of myoclonic seizure spikes was significantly higher than that of SWD spikes, and there was a greater relative voltage over M1 during myoclonic seizure spikes than in the first one to two SWD spikes.

SIGNIFICANCE

The leading sites in S1 and similar delay times suggest both SWDs and myoclonic seizures activate overlapping networks in sensorimotor cortex and thus, therapeutically targeting of this network could potentially treat both seizures. Spike focality, absolute voltage, and voltage distribution provide insight into neuronal activation during these two seizure types.

The hippocampus participates in a pharmacological rat model of absence seizures

OBJECTIVE

Using the gamma-butyrolactone (GBL) model of absence seizures in Long-Evans rats, this study investigated if 2.5-6 Hz paroxysmal discharges (PDs) induced by GBL were synchronized among the thalamocortical system and the hippocampus, and whether inactivation of the hippocampus affected PDs.

METHODS

Local field potentials were recorded by chronically implanted depth electrodes in the neocortex (frontal, parietal, visual), ventrolateral thalamus and dorsal hippocampal CA1 area. In separate experiments, multiple unit recordings were made at the hippocampal CA1 pyramidal cell layer, or the mid-septotemporal hippocampus was inactivated by local infusion of GABAA receptor agonist muscimol.

RESULTS

As PDs developed following GBL injection, coherence of local field potentials at 2.5-6 Hz increased between the hippocampus and thalamus, and between the hippocampus and the neocortex. Hippocampal theta rhythm was disrupted when GBL induced immobility in the rats. The probability of hippocampal multiple unit firing significantly increased at 40-80 ms prior to the negative peak of thalamic PDs. Coherence between hippocampal multiple unit activity and thalamic field potentials at 2.5-6 Hz was significantly increased after GBL injection. Muscimol infusion to inactivate the mid-septotemporal hippocampus, as compared to saline infusion, significantly decreased the peak frequency of the PDs induced by GBL, decreased 30-120 Hz hippocampal gamma power, and hastened the transition of PDs to 1-2 Hz slow waves.

SIGNIFICANCE

During GBL induced 2.5-6 Hz PDs, a hallmark of absence seizure, increased synchronization between the hippocampus and the thalamocortical network was indicated by frequency and temporal correlation analysis. These results suggest that the hippocampus was entrained by thalamocortical activity in the present model of absence seizures. Prolonged synchronization of the hippocampus may result in synaptic alterations that may explain the cognitive and memory deficits in some patients with absence seizures and absence status epilepticus.

Ethosuximide Affects Paired-Pulse Facilitation in Somatosensory Cortex of WAG\Rij Rats as a Model of Absence Seizure

PURPOSE

The interaction between somatosensory cortex and thalamus via a thalamocortical loop is a theory behind induction of absence epilepsy. Inside peri-oral somatosensory (S1po) and primary somatosensory forelimb (S1fl) regions, excitatory and inhibitory systems are not balanced and GABAergic inhibitory synapses seem to play a fundamental role in short-term plasticity alterations.

METHODS

We investigated the effects of Ethosuximide on presynaptic changes by utilizing paired-pulse stimulation that was recorded from somatosensory cortex in 18 WAG\Rij rats during epileptic activity. A twisted tripolar electrode including two stimulating electrodes and one recording electrode was implanted into the S1po and S1FL according to stereotaxic landmarks. Paired-pulses (200 µs, 100-1000 µA, 0.1 Hz) were applied to somatosensory cortex at 50, 100, 400, 500 ms inter-pulse intervals for 50 min period.

RESULTS

The results showed that paired-pulse facilitation was significantly reduced at all intervals in all times, but compared to the control group of epileptic WAG/Rij rats (p<0.05), it was exceptional about the first 10 minutes after the injection. At the intervals of 50 and 100 ms, a remarkable PPD was found in second, third, fourth and fifth 10-min post injection.

CONCLUSION

These experiments indicate that Ethosuximide has effects on presynaptic facilitation in somatosensory cortex inhibitory loops by alteration in GABA levels that leads to a markedly diminished PPF in paired-pulse stimulation.

Investigation of ECG Changes in Absence Epilepsy on WAG/Rij Rats

INTRODUCTION

Seizures are symptoms associated with abnormal electrical activity in electroencephalogram (EEG). The present study was designed to determine the effect of absence seizure on heart rate (HR) changes in electrocardiogram (ECG).

METHODS

HR alterations were recorded simultaneous with spike and wave discharges (SWD) by EEG in 6 WAG/Rij rats as a well characterized and validated genetic animal epilepsy model. Moreover, 6 control rats were used to distinguish the differences of HR changes between various groups. Electrodes were placed on the skull and under the chest skin, minimizing time delay and signal attenuation. HR was calculated by an adaptable algorithm based on continues wavelet transform (CWT) particular for this study. Three main features of HR; minimum, maximum, and mean values were estimated for pre-ictal and ictal intervals for all seizures.

RESULTS

ECG beats detected with sensitivity of 99.9% and positive predictability of 99.8% based on CWT. HR deceleration was found in 86% of the seizures. There were statistically significant (P<0.001) reductions of these values from pre-ictal to ictal intervals. Interictal HR acceleration and ictal deceleration were the major feature of alterations and in 23% of seizures, this decrease had priority to the onsets.

DISCUSSION

These findings may lead to design a seizure alarm system based on HR and to obtain new insights about sudden unexpected death in epilepsy (SUDEP) phenomenon and side-effects of antiepileptic drugs (AED).

Traumatic Brain Injury Causes a Tacrolimus-Sensitive Increase in Non-Convulsive Seizures in a Rat Model of Post-Traumatic Epilepsy

Epilepsy is a significant but potentially preventable complication of traumatic brain injury (TBI). Previous research in animal models of acquired epilepsy has implicated the calcium-sensitive phosphatase, calcineurin. In addition, our lab recently found that calcineurin activity in the rat hippocampus increases acutely after lateral TBI. Here we use a calcineurin inhibitor test whether an acute increase in calcineurin activity is necessary for the development of late post-traumatic seizures. Adult rats were administered the calcineurin inhibitor Tacrolimus (5mg/kg; i.p.) 1 hour after lateral fluid percussion TBI and then monitored by video-electrocorticography (video-ECoG) for spontaneous seizure activity 5 weeks or 33 weeks later. At 5 weeks post-TBI, we observed epileptiform activity on the video-ECoG of brain injured rats but no seizures. By 33 weeks post-TBI though, nearly all injured rats exhibited spontaneous seizures, including convulsive seizures which were infrequent but lasted minutes (18% of injured rats), and non-convulsive seizures which were frequent but lasted tens of seconds (94% of injured rats). We also identified non-convulsive seizures in a smaller subset of control and sham TBI rats (56%), reminiscent of idiopathic seizures described in other rats strains. Non-convulsive seizures in the brain injured rats, however, were four-times more frequent and two-times longer lasting than in their uninjured littermates. Interestingly, rats administered Tacrolimus acutely after TBI showed significantly fewer non-convulsive seizures than untreated rats, but a similar degree of cortical atrophy. The data thus indicate that administration of Tacrolimus acutely after TBI suppressed non-convulsive seizures months later.

Effect of low frequency electrical stimulation on spike and wave discharges of perioral somatosensory cortex in WAG/Rij rats

Low frequency electrical stimulation has been revealed that as a potential cure in patient with drug resistant to epilepsy. This study tries to evaluate the effect of low frequency electrical stimulation (LFS) on absence seizure of perioral region primary somatosensory cortex (S1po). Eighteen male WAG/Rij rats were received LFS (3Hz, square wave, monophasic, 200μs, and 400μA) for 25min into S1po for a period of five days. There is 6 animals per group .The stimulating electrodes were implanted according to stereotaxic landmarks and EEG recording was obtained 30min before and after LFS to analyse frequency, number and duration of spike-wave discharges (SWD). The results showed that in animals with unilateral stimulating electrodes (Exp1) in first and second days and also in animals with bilateral stimulating electrodes (Exp2) in days 3rd and 4th. LFS had significant decrease effects (p<0.05) on mean number of SWD between pre-LFS. In comparison pre-LFS to post-LFS, mean of duration in Exp2 decreased significantly. In continuous application of LFS (5 days) only the data of first day was differently significant (p<0.05) but data of other days had no difference. Comparison of data between Exp1, Exp2 and control groups showed that the mean number of Exp1 was significantly different (p<0.05) and mean pick frequency in Exp2 was significantly decreased in comparison with Exp1 group (p<0.05). The LFS of S1po produces significant antiepileptic effect on absence seizure but it was not persistent till the next day and shows a short time effect.

Focal corticothalamic sources during generalized absence seizures: a MEG study

Magnetoencephalography (MEG) was used to determine cortical and subcortical contributions to the formation of spike and wave discharges in twelve newly diagnosed, drug naïve children during forty-four generalized absence seizures. Previous studies have implicated various cortical areas and thalamic nuclei in the generation of absence seizures, but the relative timing of their activity remains unclear. Beamformer analysis using synthetic aperture magnetometry (SAM) was used to confirm the presence of independent thalamic activity, and standardized Low Resolution Brain Electromagnetic Topography (sLORETA) was used to compute statistical maps indicating source locations during absence seizures. Sources detected in the 50ms prior to the start of the seizure were more likely to be localized to the frontal cortex or thalamus. At the time of the first spike on EEG, focal source localization was seen in the lateral frontal cortex with decreased thalamic localization. Following the spike, localization became more widespread throughout the cortex. Comparison of the earliest spike and wave discharge (SWD) (Ictal Onset) and a SWD occurring 3s into the seizure (mid-Ictal) revealed significant differences during the slow wave portion of the SWDs. This study of MEG recordings in childhood absence seizures provides additional evidence that there are focal brain areas responsible for these seizures which appear bilaterally symmetric and generalized with a conventional 10-20 placement scalp EEG.