Preictal Spikes Research Articles

Seizure event detection using intravital two-photon calcium imaging data.

Intravital cellular calcium imaging has emerged as a powerful tool to investigate how different types of neurons interact at the microcircuit level to produce seizure activity, with newfound potential to understand epilepsy. Although many methods exist to measure seizure-related activity in traditional electrophysiology, few yet exist for calcium imaging. To demonstrate an automated algorithmic framework to detect seizure-related events using calcium imaging-including the detection of pre-ictal spike events, propagation of the seizure wavefront, and terminal spreading waves for both population-level activity and that of individual cells. We developed an algorithm for precise recruitment detection of population and individual cells during seizure-associated events, which broadly leverages averaged population activity and high-magnitude slope features to detect single-cell pre-ictal spike and seizure recruitment. We applied this method to data recorded using awake in vivo two-photon calcium imaging during pentylenetetrazol-induced seizures in mice. We demonstrate that our detected recruitment times are concordant with visually identified labels provided by an expert reviewer and are sufficiently accurate to model the spatiotemporal progression of seizure-associated traveling waves. Our algorithm enables accurate cell recruitment detection and will serve as a useful tool for researchers investigating seizure dynamics using calcium imaging.

Progressive generalized tonic-clonic seizures in a transgenic mouse model of adult-onset epilepsy: Implications for morphological changes in cortico-limbic and brainstem structures

Video/cortical electroencephalography (EEG) is monitored to assess progressive severity of generalized tonic clonic seizures (GTCSs) in a transgenic mouse model of adult-onset epilepsy with increased death risk. The mice overexpress the brain derived neurotrophic factor (BDNF) in the forebrain under the calcium/calmodulin dependent protein kinase 2a (termed TgBDNF) and develop GTCSs in response to tail suspension/cage agitation stimulation at 3–4 months of age. With successive GTCSs (a total of 16 across 10 weeks of assessment), seizures became more severe as evidenced by increased duration of postictal generalized EEG suppression (PGES) associated with loss of posture/consciousness. Mice also developed spike wave discharges with behavioral arrest during the seizure recovery that increased in duration as a function of number of GTCSs. Overall seizure duration (from preictal spike to offset of PGES) and ictal spectral power (full spectra) were also increased. Half of the TgBDNF mice expired following a long period of PGES at the last recorded GTCS. Seizure-evoked general arousal impairment was associated with a striking decrease in total number of gigantocellular neurons of the brainstem nucleus pontis oralis along with increase in volumes of the anterior cingulate cortex and dorsal dentate gyrus in severely convulsive TgBDNF mice compared to litter-matched WT controls and non-convulsive TgBDNF mice. The latter effect was accompanied with an increase in total number of hippocampal granule neurons. These results provide structure-function associations in an animal model of adult-onset GTCSs that progressively increase in severity with clinical relevance for sudden unexpected death following generalized seizures.

506 Fingerprinting the Epileptogenic Zone in RAVE

INTRODUCTION: The treatment of drug-resistant epilepsy remains a significant challenge. Surgical resection of the epileptogenic zone (EZ) often offers the highest chance of seizure freedom. Grinenko et al. [Brain. 2018; 141(1):117–131] demonstrated that intracranial EEG (iEEG) data analysis can be used to identify a time-frequency pattern or “fingerprint” to help identify the EZ. Complex algorithmic techniques, lack of standardization, and inaccessibility pose a hurdle to surgical programs that may consider fingerprinting as a tool to aid resection. R Analysis and Visualization of Intracranial EEG (RAVE) is a powerful, free, open-source, NIH-funded software designed to analyze iEEG data through a web browser on an internet-connected device. Here we present an accessible implementation of a fingerprinting algorithm with RAVE. METHODS: Our fingerprint module consists of three steps, following closely the work of Grinenko et al. First, iEEG seizure data is pre-processed with Morlet wavelet transform and bipolar normalization. Second, each electrode's time-frequency map is run through an image processing algorithm to extract the EZ fingerprint biomarkers: (1) pre-ictal spikes, (2) multiband fast activity, and (3) low-frequency suppression. Each electrode is ranked by biomarker and combined “fingerprint” score based on work by Woolfe et al. [J Neurosci Methods. 2019; 325:108347]. Data is then displayed via time-frequency plot for each electrode and the fingerprint score is projected across the brain with a 3D brain map viewer, RESULTS: Our fingerprint module in RAVE significantly streamlines EZ isolation. Time-consuming calculations are built-in, allowing users with no coding, image processing, or statistical experience to explore and share EZ fingerprinting data. CONCLUSIONS: We incorporated an algorithm to detect the epileptogenic zone fingerprint into RAVE, allowing free distribution and use of this research algorithm to surgical epilepsy programs.

Intracerebral Correlates of Scalp EEG Ictal Discharges Based on Simultaneous Stereo-EEG Recordings.

It remains unknown to what extent ictal scalp EEG can accurately predict the localization of the intracerebral seizure onset in presurgical evaluation of drug-resistant epilepsies. In this study, we aimed to define homogeneous ictal scalp EEG profiles (based on their first ictal abnormality) and assess their localizing value using simultaneously recorded scalp EEG and stereo-EEG. We retrospectively included consecutive patients with drug-resistant focal epilepsy who had simultaneous stereo-EEG and scalp EEG recordings of at least 1 seizure in the epileptology unit in Nancy, France. We analyzed 1 seizure per patient and used hierarchical cluster analysis to group similar seizure profiles on scalp EEG and then performed a descriptive analysis of their intracerebral correlates. We enrolled 129 patients in this study. The hierarchical cluster analysis showed 6 profiles on scalp EEG first modification. None were specific to a single intracerebral localization. The "normal EEG" and "blurred EEG" clusters (early muscle artifacts) comprised only 5 patients each and corresponded to no preferential intracerebral localization. The "temporal discharge" cluster (n = 46) was characterized by theta or delta discharges on ipsilateral anterior temporal scalp electrodes and corresponded to a preferential mesial temporal intracerebral localization. The "posterior discharge" cluster (n = 42) was characterized by posterior ipsilateral or contralateral rhythmic alpha discharges or slow waves on scalp and corresponded to a preferential temporal localization. However, this profile was the statistically most frequent scalp EEG correlate of occipital and parietal seizures. The "diffuse suppression" cluster (n = 9) was characterized by a bilateral and diffuse background activity suppression on scalp and corresponded to mesial, and particularly insulo-opercular, localization. Finally, the "frontal discharge" cluster (n = 22) was characterized by bilateral frontal rhythmic fast activity or preictal spike on scalp and corresponded to preferential ventrodorsal frontal intracerebral localizations. The hierarchical cluster analysis identified 6 seizure profiles regarding the first abnormality on scalp EEG. None of them were specific of a single intracerebral localization. Nevertheless, the strong relationships between the "temporal," "frontal," "diffuse suppression," and "posterior" profiles and intracerebral discharge localizations may contribute to hierarchize hypotheses derived from ictal scalp EEG analysis regarding intracerebral seizure onset.

Chronological changes in phase-amplitude coupling during epileptic seizures in temporal lobe epilepsy

ObjectiveTo analyze chronological changes in phase-amplitude coupling (PAC) and verify whether PAC analysis can diagnose epileptogenic zones during seizures. MethodsWe analyzed 30 seizures in 10 patients with mesial temporal lobe epilepsy who had ictal discharges with preictal spiking followed by low-voltage fast activity patterns on intracranial electroencephalography. We used the amplitude of two high-frequency bands (ripples: 80–200 Hz, fast ripples: 200–300 Hz) and the phase of three slow wave bands (0.5–1 Hz, 3–4 Hz, and 4–8 Hz) for modulation index (MI) calculation from 2 minutes before seizure onset to seizure termination. We evaluated the accuracy of epileptogenic zone detection by MI, in which a combination of MI was better for diagnosis and analyzed patterns of chronological changes in MI during seizures. ResultsMIRipples/3–4 Hz and MIRipples/4–8 Hz in the hippocampus were significantly higher than those in the peripheral regions from seizure onset. Corresponding to the phase on intracranial electroencephalography, MIRipples/3–4 Hz decreased once and subsequently increased again. MIRipples/4–8 Hz showed continuously high values. ConclusionsContinuous measurement of MIRipples/3–4 Hz and MIRipples/4–8 Hz could help identify epileptogenic zones. SignificancePAC analysis of ictal epileptic discharges can help epileptogenic zone identification.

A personalizable autonomous neural mass model of epileptic seizures

Work in the last two decades has shown that neural mass models (NMM) can realistically reproduce and explain epileptic seizure transitions as recorded by electrophysiological methods (EEG, SEEG). In previous work, advances were achieved by increasing excitation and heuristically varying network inhibitory coupling parameters in the models. Based on these early studies, we provide a laminar NMM capable of realistically reproducing the electrical activity recorded by SEEG in the epileptogenic zone during interictal to ictal states. With the exception of the external noise input into the pyramidal cell population, the model dynamics are autonomous. By setting the system at a point close to bifurcation, seizure-like transitions are generated, including pre-ictal spikes, low voltage fast activity, and ictal rhythmic activity. A novel element in the model is a physiologically motivated algorithm for chloride dynamics: the gain of GABAergic post-synaptic potentials is modulated by the pathological accumulation of chloride in pyramidal cells due to high inhibitory input and/or dysfunctional chloride transport. In addition, in order to simulate SEEG signals for comparison with real seizure recordings, the NMM is embedded first in a layered model of the neocortex and then in a realistic physical model. We compare modeling results with data from four epilepsy patient cases. By including key pathophysiological mechanisms, the proposed framework captures succinctly the electrophysiological phenomenology observed in ictal states, paving the way for robust personalization methods based on NMMs.

Learning to define an electrical biomarker of the epileptogenic zone.

The role of fast activity as a potential biomarker in localization of the epileptogenic zone (EZ) remains controversial due to recently reported unsatisfactory performance. We recently identified a “fingerprint” of the EZ as a time‐frequency pattern that is defined by a combination of preictal spike(s), fast oscillatory activity, and concurrent suppression of lower frequencies. Here we examine the generalizability of the fingerprint in application to an independent series of patients (11 seizure‐free and 13 non‐seizure‐free after surgery) and show that the fingerprint can also be identified in seizures with lower frequency (such as beta) oscillatory activity. In the seizure‐free group, only 5 of 47 identified EZ contacts were outside the resection. In contrast, in the non‐seizure‐free group, 104 of 142 identified EZ contacts were outside the resection. We integrated the fingerprint prediction with the subject's MR images, thus providing individualized anatomical estimates of the EZ. We show that these fingerprint‐based estimates in seizure‐free patients are almost always inside the resection. On the other hand, for a large fraction of the nonseizure‐free patients the estimated EZ was not well localized and was partially or completely outside the resection, which may explain surgical failure in such cases. We also show that when mapping fast activity alone onto MR images, the EZ was often over‐estimated, indicating a reduced discriminative ability for fast activity relative to the full fingerprint for localization of the EZ.

Not Just Where, But How Does a Seizure Start?

To this end, we analyzed 820 seizures from 252 consecutive patients explored by stereoelectroencephalography (total of 2148 electrodes), including various forms of focal refractory epilepsies. We used a reproducible method combining visual and time-frequency analyses. We described 8 SOPs: low-voltage fast activity (LVFA), preictal spiking followed by LVFA, burst of polyspikes followed by LVFA, slow wave/DC shift followed by LVFA, sharp theta/alpha waves, beta sharp waves, rhythmic spikes/spike-waves, and delta-brush. Low-voltage fast activity occurred in 79% of patients. The SOP was significantly associated with (1) underlying etiology (burst of polyspikes followed by LVFA with the presence of a focal cortical dysplasia, LVFA with malformation of cortical development, postvascular and undetermined epilepsies), (2) spatial organization of the epileptogenic zone (EZ; burst of polyspikes followed by LVFA with focal organization, slow wave/DC shift followed by LVFA with network organization), and (3) postsurgical seizure outcome (better outcome when LVFA present). This study demonstrates that the main determinants of the SOP are the underlying etiology and the spatial organization of the EZ. Concerning the postsurgical seizure outcome, the main determinant factor is the spatial organization of the EZ, but the SOP plays also a role, conferring better prognosis when LVFA is present.

The repertoire of seizure onset patterns in human focal epilepsies: Determinants and prognostic values.

In this study, we seek to analyze the determinants of the intracranial electroencephalography seizure onset pattern (SOP) and the impact of the SOP in predicting postsurgical seizure outcome. To this end, we analyzed 820 seizures from 252 consecutive patients explored by stereo-electroencephalography (total of 2148 electrodes), including various forms of focal refractory epilepsies. We used a reproducible method combining visual and time-frequency analyses. We described eight SOPs: low-voltage fast activity (LVFA), preictal spiking followed by LVFA, burst of polyspikes followed by LVFA, slow wave/DC shift followed by LVFA, sharp theta/alpha waves, beta sharp waves, rhythmic spikes/spike-waves, and delta-brush. LVFA occurred in 79% of patients. The seizure onset pattern was significantly associated with (1) underlying etiology (burst of polyspikes followed by LVFA with the presence of a focal cortical dysplasia, LVFA with malformation of cortical development, postvascular and undetermined epilepsies), (2) spatial organization of the epileptogenic zone (EZ; burst of polyspikes followed by LVFA with focal organization, slow wave/DC shift followed by LVFA with network organization), and (3) postsurgical seizure outcome (better outcome when LVFA present). This study demonstrates that the main determinants of the SOP are the underlying etiology and the spatial organization of the EZ. Concerning the postsurgical seizure outcome, the main determinant factor is the spatial organization of the EZ, but the SOP plays also a role, conferring better prognosis when LVFA is present.

Characteristics of EEG Seizure-Onset Patterns Recorded From Subdural Electrodes Over MRI-Visible Frontal Focal Cortical Dysplasia Type IIb Lesions.

Focal cortical dysplasia (FCD) is intrinsically epileptogenic, and an MRI-visible lesion typically constitutes the core part of the epileptogenic zone. We aimed to identify ictal EEG patterns that represent the epileptogenic zone by using subdural electrodes placed over the MRI-visible FCD lesion. We selected seven patients with frontal lobe epilepsy caused by pathologically proven FCD type IIb who underwent preoperative intracranial EEG evaluation with subdural electrodes followed by resection surgery with seizure-free outcome. The characteristics of ictal EEG patterns, interictal/ictal high-frequency oscillations, and ictal direct current shifts from intracranial electrodes placed over the MRI-visible lesion were analyzed. Two seizure-onset patterns (low voltage fast activity and fast spike activity) were identified. Low voltage fast activity was seen in all patients with a lateral frontal lesion, and it was always preceded by preictal spikes. Fast spike activity occurred only in patients with a mesial frontal lesion. Interictal/ictal high-frequency oscillations and ictal direct current shifts were seen in all patients. The epileptogenic zone of frontal FCD type IIb may be characterized by EEG seizure-onset patterns consisting of low voltage fast activity and fast spike activity accompanied by ictal high-frequency oscillations and ictal direct current shifts. Further study is needed to determine whether other seizure-onset patterns exist in patients with FCD type IIb.

Seizure-onset patterns in focal cortical dysplasia and neurodevelopmental tumors: Relationship with surgical prognosis and neuropathologic subtypes.

The study of intracerebral electroencephalography (EEG) seizure-onset patterns is crucial to accurately define the epileptogenic zone and guide successful surgical resection. It also raises important pathophysiologic issues concerning mechanisms of seizure generation. Until now, several seizure-onset patterns have been described using distinct recording methods (subdural, depth electrode), mostly in temporal lobe epilepsies or with heterogeneous neocortical lesions. We analyzed data from a cohort of 53 consecutive patients explored by stereoelectroencephalography (SEEG) and with pathologically confirmed malformation of cortical development (MCD; including focal cortical dysplasia [FCD] and neurodevelopmental tumors [NDTs]). We identified six seizure-onset patterns using visual and time-frequency analysis: low-voltage fast activity (LVFA); preictal spiking followed by LVFA; burst of polyspikes followed by LVFA; slow wave/DC shift followed by LVFA; theta/alpha sharp waves; and rhythmic spikes/spike-waves. We found a high prevalence of patterns that included LVFA (83%), indicating nevertheless that LVFA is not a constant characteristic of seizure onset. An association between seizure-onset patterns and histologic types was found (p = 001). The more prevalent patterns were as follows: (1) in FCD type I LVFA (23.1%) and slow wave/baseline shift followed by LVFA (15.4%); (2) in FCD type II burst of polyspikes followed by LVFA (31%), LVFA (27.6%), and preictal spiking followed by LVFA (27.6%); (3) in NDT, LVFA (54.5%). We found that a seizure-onset pattern that included LVFA was associated with favorable postsurgical outcome, but the completeness of the EZ resection was the sole independent predictive variable. Six different seizure-onset patterns can be described in FCD and NDT. Better postsurgical outcome is associated with patterns that incorporate LVFA.

Interictal spikes and epileptic seizures: their relationship and underlying rhythmicity.

We report on a quantitative analysis of electrocorticography data from a study that acquired continuous ambulatory recordings in humans over extended periods of time. The objectives were to examine patterns of seizures and spontaneous interictal spikes, their relationship to each other, and the nature of periodic variation. The recorded data were originally acquired for the purpose of seizure prediction, and were subsequently analysed in further detail. A detection algorithm identified potential seizure activity and a template matched filter was used to locate spikes. Seizure events were confirmed manually and classified as either clinically correlated, electroencephalographically identical but not clinically correlated, or subclinical. We found that spike rate was significantly altered prior to seizure in 9 out of 15 subjects. Increased pre-ictal spike rate was linked to improved predictability; however, spike rate was also shown to decrease before seizure (in 6 out of the 9 subjects). The probability distribution of spikes and seizures were notably similar, i.e. at times of high seizure likelihood the probability of epileptic spiking also increased. Both spikes and seizures showed clear evidence of circadian regulation and, for some subjects, there were also longer term patterns visible over weeks to months. Patterns of spike and seizure occurrence were highly subject-specific. The pre-ictal decrease in spike rate is not consistent with spikes promoting seizures. However, the fact that spikes and seizures demonstrate similar probability distributions suggests they are not wholly independent processes. It is possible spikes actively inhibit seizures, or that a decreased spike rate is a secondary symptom of the brain approaching seizure. If spike rate is modulated by common regulatory factors as seizures then spikes may be useful biomarkers of cortical excitability.

Intracranial electrographic analysis of preictal spiking and ictal onset in uni- and bitemporal epilepsy.

Ictal onset patterns in bilateral mesial temporal lobe epilepsy have not been comprehensively studied. A retrospective review of intracranial electrographic data was undertaken to establish whether it is possible to distinguish between unilateral and bilateral mesial temporal lobe epilepsy based on ictal onset patterns, including periodic preictal spiking. A total of 470 ictal onset patterns were analyzed by bitemporal extraoperative electrocorticography in 13 patients with medically intractable mesial temporal lobe epilepsy. Ictal onset patterns were categorized, by frequency, as type A (<12 Hz), type B (12-40 Hz) and type C (>40 Hz). Preictal rhythmic spiking, of at least five seconds duration, and time to contralateral propagation were also measured with each ictal event. We determined if the proportion of "ictal onset pattern frequencies" or "incidence of preictal spiking" differed between unilateral and bilateral mesial temporal lobe epilepsy. Seven patients with unilateral mesial temporal lobe epilepsy received surgery and achieved Engel class I outcomes, while the remaining six did not undergo resective surgery, due to the bilateral ictal onsets in extraoperative electrocorticography. The proportion of patients experiencing any preictal spikes was higher in unitemporal than in bitemporal cases (100% vs 50%;p=0.069). Ofthe470 ictal onset patterns analyzed (174 unitemporal and 296 bitemporal), a significant greater percentage of preictal spikes was found in unilateral cases (78% unitemporal vs 14% bitemporal; p=0.002). Low-frequency patterns were more evident in bitemporal cases (45%) than in unitemporal (10%), although the difference was not statistically significant (p=0.129). No differences were detected between the unitemporal and bitemporal groups regarding age at onset or at presentation. A greater proportion of pre ictal spiking, based on extraoperative electrocorticography, was present in unilateral, compared to bilateral, mesial temporal lobe epilepsy. Further studies are warranted to determine the causal significance of preictal spiking in mesial temporal lobe epilepsy.

Synchronous inhibitory potentials precede seizure-like events in acute models of focal limbic seizures.

Interictal spikes in models of focal seizures and epilepsies are sustained by the synchronous activation of glutamatergic and GABAergic networks. The nature of population spikes associated with seizure initiation (pre-ictal spikes; PSs) is still undetermined. We analyzed the networks involved in the generation of both interictal and PSs in acute models of limbic cortex ictogenesis induced by pharmacological manipulations. Simultaneous extracellular and intracellular recordings from both principal cells and interneurons were performed in the medial entorhinal cortex of the in vitro isolated guinea pig brain during focal interictal and ictal discharges induced in the limbic network by intracortical and brief arterial infusions of either bicuculline methiodide (BMI) or 4-aminopyridine (4AP). Local application of BMI in the entorhinal cortex did not induce seizure-like events (SLEs), but did generate periodic interictal spikes sensitive to the glutamatergic non-NMDA receptor antagonist DNQX. Unlike local applications, arterial perfusion of either BMI or 4AP induced focal limbic SLEs. PSs just ahead of SLE were associated with hyperpolarizing potentials coupled with a complete blockade of firing in principal cells and burst discharges in putative interneurons. Interictal population spikes recorded from principal neurons between two SLEs correlated with a depolarizing potential. We demonstrate in two models of acute limbic SLE that PS events are different from interictal spikes and are sustained by synchronous activation of inhibitory networks. Our findings support a prominent role of synchronous network inhibition in the initiation of a focal seizure.

Selective activation of parvalbumin- or somatostatin-expressing interneurons triggers epileptic seizurelike activity in mouse medial entorhinal cortex.

GABAergic interneurons are thought to play a critical role in eliciting interictal spikes (IICs) and triggering ictal discharges in temporal lobe epilepsy, yet the contribution of different interneuronal subtypes to seizure initiation is still largely unknown. Here we took advantage of optogenetic techniques combined with patch-clamp and field recordings to selectively stimulate parvalbumin (PV)- or somatostatin (SOM)-positive interneurons expressing channelrhodopsin-2 (CHR-2) in layers II-III of adult mouse medial entorhinal cortical slices during extracellular perfusion with the proconvulsive compound 4-aminopyridine (4-AP, 100-200 μM). In control conditions, blue laser photostimulation selectively activated action potential firing in either PV or SOM interneurons and, in both cases, caused a robust GABAA-receptor-mediated inhibition in pyramidal cells (PCs). During perfusion with 4-AP, brief photostimuli (300 ms) activating either PV or SOM interneurons induced patterns of epileptiform activity that closely replicated spontaneously occurring IICs and tonic-clonic ictal discharges. Laser-induced synchronous firing in both interneuronal types elicited large compound GABAergic inhibitory postsynaptic currents (IPSCs) correlating with IICs and preictal spikes. In addition, spontaneous and laser-induced epileptic events were similarly initiated in concurrence with a large increase in extracellular potassium concentration. Finally, interneuron activation was unable to stop or significantly shorten the progression of seizurelike episodes. These results suggest that entorhinal PV and SOM interneurons are nearly equally effective in triggering interictal and ictal discharges that closely resemble human temporal lobe epileptic activity.

Cortical epileptogenesis of slowly kindled freely moving rats

Abstract Objective. Epilepsy is a neurological disorder that can be caused by many underlying pathologies. The epileptic and interictal manifestations that appear during the progression of chronic epilepsy are still not understood completely. One of the most frequent forms of this disease is temporal lobe epilepsy in which is clear involvement of the hippocampal formation. In order to study the electrografic progression of untreated seizures we used amygdala kindling in freely moving rats. Methods. Seven animals were implanted with bilateral hippocampal and prefrontal electrodes. A bipolar electrode, implanted in the lateral nuclei of the left amygdala was used for stimulation. The kindled group of animals was stimulated daily with the minimum current intensity needed to reach the afterdischarge threshold. Behavioral changes during kindling were scored according to the Racine scale. Results. The average seizure severity on the Racine scale was 2.6±0.4 by day 6 and 4.4±0.6 by day 20. The first spontaneous seizures appeared after 31 days of stimulation. During spontaneous seizures the preictal spike full width at half maximum increased gradually from 51±4msec to 110±5msec (p &lt; 0.05) whereas the amplitude of the negative field potential deflection increased by 62% (p &lt; 0.05). Conclusions. Our study showed that the progression of temporal lobe epilepsy, as seen in humans, can be reproduced in the kindling model with high fidelity. This study confirms in vivo the increase in preictal spike duration as well as the increase of the amplitude of negative field potential deflection during the preictal period.

A novel spatiotemporal analysis of peri-ictal spiking to probe the relation of spikes and seizures in epilepsy.

The relation between epileptic spikes and seizures is an important but still unresolved question in epilepsy research. Preclinical and clinical studies have produced inconclusive results on the causality or even on the existence of such a relation. We set to investigate this relation taking in consideration seizure severity and spatial extent of spike rate. We developed a novel automated spike detection algorithm based on morphological filtering techniques and then tested the hypothesis that there is a pre-ictal increase and post-ictal decrease of the spatial extent of spike rate. Peri-ictal (around seizures) spikes were detected from intracranial EEG recordings in 5 patients with temporal lobe epilepsy. The 94 recorded seizures were classified into two classes, based on the percentage of brain sites having higher or lower rate of spikes in the pre-ictal compared to post-ictal periods, with a classification accuracy of 87.4%. This seizure classification showed that seizures with increased pre-ictal spike rate and spatial extent compared to the post-ictal period were mostly (83%) clinical seizures, whereas no such statistically significant (α=0.05) increase was observed peri-ictally in 93% of sub-clinical seizures. These consistent across patients results show the existence of a causal relation between spikes and clinical seizures, and imply resetting of the preceding spiking process by clinical seizures.

Independent Epileptiform Discharge Patterns in the Olfactory and Limbic Areas of the In Vitro Isolated Guinea Pig Brain During 4-Aminopyridine Treatment

In vitro studies performed on brain slices demonstrate that the potassium channel blocker 4-aminopyridine (4AP, 50 microM) discloses electrographic seizure activity and interictal discharges. These epileptiform patterns have been further analyzed here in a isolated whole guinea pig brain in vitro by using field potential recordings in olfactory and limbic structures. In 8 of 13 experiments runs of fast oscillatory activity (fast runs, FRs) in the piriform cortex (PC) propagated to the lateral entorhinal cortex (EC), hippocampus and occasionally to the medial EC. Early and late FRs were asynchronous in the hemispheres showed different duration [1.78 +/- 0.51 and 27.95 +/- 4.55 (SD) s, respectively], frequency of occurrence (1.82 +/- 0.49 and 34.16 +/- 6.03 s) and frequency content (20-40 vs. 40-60 Hz). Preictal spikes independent from the FRs appeared in the hippocampus/EC and developed into ictal-like discharges that did not propagate to the PC. Ictal-like activity consisted of fast activity with onset either in the hippocampus (n = 6) or in the mEC (n = 2), followed by irregular spiking and sequences of diffusely synchronous bursts. Perfusion of the N-methyl-d-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid (100 microM) did not prevent FRs, increased the duration of limbic ictal-like discharges and favored their propagation to olfactory structures. The AMPA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (50 microM) blocked ictal-like events and reduced FRs. In conclusion, 4AP-induced epileptiform activities are asynchronous and independent in olfactory and hippocampal-entorhinal regions. Epileptiform discharges in the isolated guinea pig brain show different pharmacological properties compared with rodent in vitro slices.

Anti-glutamatergic effect of riluzole: Comparison with valproic acid

Riluzole, an anti-amyotrophic lateral sclerosis drug, known to decrease presynaptic glutamate release, is viewed as a candidate supplementary medication for epilepsy. In the present study, we compared the effects of riluzole and valproate (VPA) in the pilocarpine-induced limbic seizure model and in the γ-hydroxybutyrate lactone (GBL)-induced absence seizure model. We applied immunohistochemical study for vesicular transporter 1 (VGLUT1) and extracellular recording in the rat dentate gyrus of both pilocarpine- and GBL-induced seizure models to measure effects of riluzole and VPA. Both VPA and riluzole treatments reduced VGLUT1 immunoreactivity. Riluzole treatment completely inhibited pre-ictal spikes and spike-wave discharges in the pilocarpine- and GBL-induced epilepsy models, whereas VPA partially inhibited these phenomena. In both seizure models, the anti-epileptic effects of VPA and riluzole are basically related to anti-glutamatergic (reducing field excitatory postsynaptic potential slope and excitability ratio), not GABAergic (paired-pulse inhibition) effect. Riluzole was more effective at reducing seizure activity in both epilepsy models than VPA. These results suggest that riluzole is a potential antiepileptic drug with activity against limbic seizure and absence seizure.

Propagation Dynamics of Epileptiform Activity Acutely Induced by Bicuculline in the Hippocampal–Parahippocampal Region of the Isolated Guinea Pig Brain

Aim of the study is to investigate the involvement of parahippocampal subregions in the generation and in the propagation of focal epileptiform discharges in an acute model of seizure generation in the temporal lobe induced by arterial application of bicuculline in the in vitro isolated guinea pig brain preparation. Electrophysiological recordings were simultaneously performed with single electrodes and multichannel silicon probes in the entorhinal, perirhinal, and piriform cortices and in the area CA1 of the hippocampus of the in vitro isolated guinea pig brain. Interictal and ictal epileptiform discharges restricted to the temporal region were induced by a brief (3-5 min) arterial perfusion of the GABA(A) receptor antagonist, bicuculline methiodide (50 microM). Current source density analysis of laminar field profiles performed with the silicon probes was carried out at different sites to establish network interactions responsible for the generation of epileptiform potentials. Nonlinear regression analysis was conducted on extracellular recordings during ictal onset in order to quantify the degree of interaction between fast activities generated at different sites, as well as time delays. Experiments were performed in 31 isolated guinea pig brains. Bicuculline-induced interictal and ictal epileptiform activities that showed variability of spatial propagation and time course in the olfactory-temporal region. The most commonly observed pattern (n = 23) was characterized by the initial appearance of interictal spikes (ISs) in the piriform cortex (PC), which propagated to the lateral entorhinal region. Independent and asynchronous preictal spikes originated in the entorhinal cortex (EC)/hippocampus and progressed into ictal fast discharges (around 25 Hz) restricted to the entorhinal/hippocampal region. The local generation of fast activity was verified and confirmed both by CSD and phase shift analysis performed on laminar profiles. Fast activity was followed by synchronous afterdischarges that propagated to the perirhinal cortex (PRC) (but not to the PC). Within 1-9 min, the ictal discharge ceased and a postictal period of depression occurred, after which periodic ISs in the PC resumed. Unlike preictal ISs, postictal ISs propagated to the PRC. Several studies proposed that reciprocal connections between the entorhinal and the PRC are under a very efficient inhibitory control (1). We report that ISs determined by acute bicuculline treatment in the isolated guinea pig brain progress from the PC to the hippocampus/EC just before ictal onset. Ictal discharges are characterized by a peculiar pattern of fast activity that originates from the entorhinal/hippocampal region and only secondarily propagates to the PRC. Postictal propagation of ISs to the PRC occurred exclusively when an ictal discharge was generated in the hippocampal/entorhinal region. The results suggest that reiteration of ictal events may promote changes in propagation pattern of epileptiform discharges that could act as trigger elements in the development of temporal lobe epilepsy.