Biomedical subjects

F Bartolomei

Publications and source records attributed to F Bartolomei.

At least 19 recordsLinked to original sources

PubMed2005

1H-MRS imaging in intractable frontal lobe epilepsies characterized by depth electrode recording.

Presurgical evaluation of frontal lobe epilepsy (FLE) remains a challenging issue and frequently requires invasive depth electrode recording. In this study, we aimed at evaluating the potential usefulness of a non-invasive technique such as proton magnetic resonance spectroscopic imaging ((1)H-MRSI) in the presurgical evaluation of FLE and at investigating the potential electrophysiological correlates of the metabolic disturbances as defined by (1)H-MRSI. We compared the distribution of (1)H-MRSI abnormalities with the electrophysiological abnormalities defined by stereo-electroencephalography (SEEG) recording in 12 patients presenting with several subtypes of FLE. We also used 12 control subjects in order to obtain normative (1)H-MRSI data. We used a multilevel (1)H-MRSI protocol to better sample the principal regions of the frontal lobe. We also applied a metabolic mapping technique allowing a visual display of metabolic data. A significant decrease of both N-acetyl-aspartate/phosphocreatine-creatine and N-acetyl-aspartate/(choline-compounds + phosphocreatine-creatine) ratios was observed in regions involved in the epileptogenic zone (EZ) and/or the irritative zone (IZ) compared to regions without electrical abnormalities in the same patients (P = 0.044 and P = 0.018, respectively), and also compared to controls (P = 0.004 and P = 0.0001, respectively). No significant differences in metabolic ratios were observed between those regions involved in the EZ and those involved in the IZ only. Our results suggest a link between the relative decrease of N-acetyl-aspartate and the EZ as well as the IZ in FLE. Thus, multilevel (1)H-MRSI protocol may add pertinent information during the non-invasive presurgical evaluation of FLE.

Adolescent↗

PubMed2005

A method to identify reproducible subsets of co-activated structures during interictal spikes. Application to intracerebral EEG in temporal lobe epilepsy.

OBJECTIVE: We present a novel quantitative method to statistically analyze the distribution of multichannel intracerebral interictal spikes (multi-IIS) in stereoelectroencephalographic (SEEG) recordings. The method automatically extracts groups of brain structures conjointly and frequently involved in the generation of interictal activity. These groups are referred to as 'subsets of co-activated structures' (SCAS). We applied the method to long duration interictal recordings in patients with mesial temporal lobe epilepsy (MTLE) and analyzed the reproducibility of subsets of structures involved in the generation of multi-IIS for each patient and among patients. METHODS: Fifteen patients underwent long-term intracerebral EEG recording (SEEG technique) using depth electrodes. A 1 h period of continuous interictal EEG recording was selected for each patient with precautions regarding the time after anesthesia pre-SEEG, the temporal distance with respect to seizures, the vigilance state of the patient, and the anti-epileptic drug withdrawal. A research of SCAS was conducted on each recording using the developed method that includes 3 steps: (i) automatic detection of monochannel intracerebral interictal spikes (mono-IIS), (ii) formation of multi-IIS using a temporal sliding window, and (iii) extraction of SCAS. In the third step, statistical tests are used to evaluate the frequency of multi-IIS as well as their significance (with respect to the 'random distribution of mono-IIS' case). RESULTS: In each patient, several thousands of multi-IIS (mean+/-SD, 3322+/-2190) were formed and several SCAS (mean+/-SD, 3.80+/-1.47) were automatically extracted. Results show that reproducible subsets of brain structures are involved in the generation of interictal activity. Although SCAS were found to be variable from one patient to another, some invariant information was pointed up. In all patients, multi-IIS distribute over two distinct groups of structures: mesial structures (15/15) and lateral structures (7/15). Moreover, two particular structures, the internal temporal pole and the temporo-basal cortex, may be conjointly involved with either the first or the second group. Finally, some extracted SCAS seem to match well-defined anatomo-functional circuits of the temporal lobe. CONCLUSIONS AND SIGNIFICANCE: During interictal activity in MTLE, similar subsets of temporal lobe structures are involved in the generation of spikes. This paper brings statistical evidence for the existence of these subsets and presents a method to automatically extract them from SEEG recordings. Interictal activity is spatially organized in the temporal lobe and preferentially involves two functional systems of the temporal lobe (either mesial or lateral).

Adolescent↗

PubMed2005

[Spatio-temporal dynamics of neuronal networks in partial epilepsy].

INTRODUCTION: The anatomo-functional organization of partial drug-resistant epilepsies is the subject of much current research aiming at better understanding these pathologies and improving their treatment. The work carried out by our team on the study of intracerebral recording falls within this category of research. The objectives are to identify the neural networks involved in the generation of paroxysmal activity and to understand their spatio-temporal dynamics, in order to be able in the long term to propose targeted therapeutic approaches likely to "control" these networks. STATE OF ART: The traditional concept of epileptic "focus" must nowadays be replaced by a more complex model taking into account potential interactions within the neural networks involved in the seizure. Indeed, during partial seizures, involved cerebral structures are the site of characteristic oscillations which may be synchronized or on the contrary transiently desynchronized. These epileptic rhythms may disturb the physiological rhythms underlying normal cognitive processes; these cognitive processes may thus be impaired in partial epilepsy, even those remote from the site of origin of the discharge. In this article we describe a model of organization of human partial seizures, through characterization of the relationships ("synchrony") between intracerebral signals recorded in the involved structures. We propose that seizures are generated in an initial network of highly epileptogenic brain structures (epileptogenic zone network, EZN) whose activity is synchronized; this activity is then transiently desynchronized with the appearance of fast oscillations. During a second ictal phase, other cortical and subcortical structures are the seat of slower rhythmic modifications that are synchronized (propagation network, PN). The emergence of a particular clinical semiology in the course of the seizure depends on these phenomena which can in certain cases "mimic" a normal cerebral process or on the contrary provoke a major rupture in normal cerebral functioning. CONCLUSIONS: These studies contribute to improvement in our knowledge of the neural networks involved in partial epilepsies. In the future, this type of research may contribute to the development of specific treatments that target certain pathophysiological mechanisms involved in seizure generation.

Brain↗

PubMed2004

Cortical stimulation study of the role of rhinal cortex in déjà vu and reminiscence of memories.

OBJECTIVE: To study the role of perirhinal (PC) and entorhinal cortices (EC) in dreamy state symptoms (déjà vu and reminiscence of scenes). These phenomena have been attributed to functional alteration of memory networks supported by the medial temporal lobes, principally involving the amygdala and hippocampus. The role of sub-hippocampal structures (EC and PC) in inducing these phenomena has not previously been addressed. METHODS: The authors studied the symptoms evoked by direct electrical stimulations of PC and EC in comparison with those obtained after stimulation of the amygdala and hippocampus. Stimulations were performed in a group of 24 patients with epilepsy, during stereoelectroencephalographic (SEEG) recordings in the setting of presurgical evaluation. All patients had electrodes that sampled the rhinal cortices, amygdala, and hippocampus. RESULTS: A total of 280 stimulations were analyzed. Entorhinal and perirhinal stimulations induced classic mesial temporal lobe responses (emotional, dysautonomic) but also more specific responses, particularly the déjà vu phenomenon and reminiscence of scenes. Such déjà vu or déjà vécu type responses were produced proportionately more often by stimulation of the EC than by stimulation of the amygdala and hippocampus. In particular, déjà vu was associated with stimulation of the EC and reminiscence of memories with PC stimulation. CONCLUSION: This study strongly suggests that experiential symptoms are largely dependent upon functional modification of the physiology of the rhinal cortices.

Adult↗

PubMed2004

Gamma knife surgery for epilepsy related to hypothalamic hamartomas.

OBJECTIVE: Drug resistant epilepsy associated with hypothalamic hamartoma (HH) can be cured by microsurgical resection of the lesion. Morbidity and mortality risks of microsurgery in this area are significant. Gamma Knife Surgery's (GKS) reduced invasivity seems to be well adapted. In view of the severity of the disease and risks of surgical resection it is crucial to evaluate GKS for this indication. A first retrospective study has shown a very good safety and efficacy level but for a more reliable evaluation a prospective study would be required. METHODS: Between Oct 1999 and July 2002, 30 patients with HH and associated severe epilepsy were included. Seizure semiology (video EEG) and frequency, behavioural disturbances, neuropsychological performance, endocrinological status, sleep electroclinical abnormalities, MR imaging, and visual function were systematically evaluated before and after GKS (6, 12, 18, 24, 36 months). Twenty patients had experienced precocious puberty at a median age of 3,7 (0-9). Range of maximum diameter was from 7,5 to 23 mm with only 3 larger than 18 mm. The median marginal dose was 17 gy (14-20). RESULTS: Sufficient follow up for final evaluation is not yet available. Only 6 patients have a follow-up of more than 12 months and 19 more than 6 months. However a lot of very dramatic changes did occur during that period in this group. Among the 19 patients with more than 6 months of follow-up, a lot had already experienced an increase of gelastic seizures around 3 months (3), an improvement in their seizure rate (18), behaviour (9), sleep (3), and EEG background activity (3), a cessation of partial complex seizures (7). No complications have occurred till now except one patient experiencing at 5 months a hyperthermia without infection and concomitant increase of gelastic seizures both ceasing suddenly and spontaneously after 15 days. CONCLUSION: Our first results indicate that GKS is as effective as microsurgical resection and very much safer. GKS also allows to avoid the vascular risk related to radiofrequency lesioning or stimulation. The disadvantage of radiosurgery is its delayed action. Longer follow-up is mandatory for a serious evaluation of the role of GKS. Results are faster and more complete in patients with smaller lesions inside the 3rd ventricle (grade II). The early effect on subclinical discharges turns out to play a major role in the dramatic improvement of sleep quality, behaviour, developmental acceleration at school.

Adolescent↗

PubMed2004

[EEG and video-EEG explorations in refractory partial epilepsy].

The assessment of drug -resistant partial epilepsy by electrophysiological explorations (based on non-invasive EEG) involves two types of analysis: the study of the seizures, primarily by video-EEG exploration, and the study of interictal activities based on visual analysis, and in some centers on techniques of source localization (high resolution EEG and magnetoencephalography, MEG). Seizure recording can be used to confirm the focal nature and the epileptic origin of the seizure as well as other features such as severity (secondary generalization, frequency, falls etc.). In the pre-surgical approach, the video-EEG recordings enable study of the electro-clinical correlations and allow assumptions on the anatomical localization of the epileptogenic zone. Precise analysis of the localization of the interictal activities (especially within the framework of extra-temporal epilepsies) based on source localization methods, makes it possible to put forth assumptions on the localization of the irritative zone.

Anticonvulsants↗

PubMed2003

Epileptic fast intracerebral EEG activity: evidence for spatial decorrelation at seizure onset.

Low-voltage rapid discharges (or fast EEG ictal activity) constitute a characteristic electrophysiological pattern in focal seizures of human epilepsy. They are characterized by a decrease of signal voltage with a marked increase of signal frequency (typically beyond 25 Hz). They have long been observed in stereoelectroencephalographic (SEEG) signals recorded with intra-cerebral electrodes, generally occurring at seizure onset and simultaneously involving distinct brain regions. Spectral properties of rapid ictal discharges as well as spatial correlations measured between SEEG signals generated from distant sites before, during and after these discharges were studied. Cross-correlation estimates within typical EEG sub-bands and statistical tests performed in 10 patients suffering from partial epilepsy (frontal, temporal or fronto-temporal) reveal that SEEG signals are significantly de-correlated during the discharge period compared with periods that precede and follow this discharge. These results can be interpreted as a functional decoupling of distant brain sites at seizure onset followed by an abnormally high re-coupling when the seizure develops. They lead to the concept of 'disruption' that is complementary of that of 'activation' (revealed by significantly high correlations between signals recorded during seizures), both giving insights into our understanding of pathophysiological processes involved in human partial epilepsies as well as in the interpretation of clinical semiology.

Adolescent↗

PubMed2002

Gamma Knife surgery, a neuromodulation therapy in epilepsy surgery!

INTRODUCTION: The more classical approach for Epilepsy surgery is the removal of the epileptogenic zone (ZE). We present a critical review of information in favor of a possible non-destructive effect of radiosurgery in epilepsy surgery. MATERIAL: Clinical material of patients with epilepsies related to a lesion in highly functional areas subjected to radiosurgery with relief of the seizures and no functional worsening is available. We applied direct treatment of the EZ with good efficacy in the absence of destructive aspects on the MR and no functional deterioration (e.g. hypothalamic hamartomas). Experimental studies have shown biochemical differential effect of radiosurgery on the striatum, glial cell elimination, stem cell migration toward the target area, sprouting,... Plasticity phenomenon are induced by radiosurgery when using non necrotizing dosemetry. DISCUSSION: There is clinical and experimental evidence of Gamma Knife capability to induce modulation in the neural system. Detailed mechanism of this modulation and dosemetric parameters enabling to induce such plasticity with no necrosis are still unknown. Subpial transection turning out actually to be quite disappointing, there is a specific rationale to test radiosurgery capability to treat EZ cortex while preserving the underlying function of this cortex when the functional risk for cortectomy is too high.

Brain Diseases↗

PubMed2002

Epileptic fast activity can be explained by a model of impaired GABAergic dendritic inhibition.

This paper focuses on high-frequency (gamma band) EEG activity, the most characteristic electrophysiological pattern in focal seizures of human epilepsy. It starts with recent hypotheses about: (i) the behaviour of inhibitory interneurons in hippocampal or neocortical networks in the generation of gamma frequency oscillations; (ii) the nonuniform alteration of GABAergic inhibition in experimental epilepsy (reduced dendritic inhibition and increased somatic inhibition); and (iii) the possible depression of GABA(A,fast) circuit activity by GABA(A,slow) inhibitory postsynaptic currents. In particular, these hypotheses are introduced in a new computational macroscopic model of EEG activity that includes a physiologically relevant fast inhibitory feedback loop. Results show that strikingly realistic activity is produced by the model when compared to real EEG signals recorded with intracerebral electrodes. They show that, in the model, the transition from interictal to fast ictal activity is explained by the impairment of dendritic inhibition.

Action Potentials↗

PubMed2002

What role for radiosurgery in mesial temporal lobe epilepsy.

SUMMARY: The Gamma Knife radiosurgery is a neurosurgical approach having now demonstrated well its efficiency, its low morbidity and its comfort in the treatment of numerous neurosurgical disorders. These advantages of this type of intervention make it a method of great interest in functional neurosurgery and quite particularly in surgery of epilepsy. French experience is a pioneer one in this domain. Since for several years the positive evolution of the epilepsy associated with brain lesions had been noticed after radiosurgical Gamma Knife treatment, the use of this approach in surgery of epilepsy has been systematically evaluated since 1993. Data are today available concerning the surgical treatment of the epilepsies originating in the temporomesial area without space-occupying process, epilepsies associated to hypothalamic hamartomas and epilepsies associated with cavernous angiomas or low grade gliomas. The quality of the epileptological result obtained in these various indications associated with a very reduced morbidity lets assume that the Gamma Knife radiosurgery could indeed have tomorrow a place within the sample group of surgical approaches dedicated to the treatment of severe epilepsies. However, a larger number of treated patients and a more prolonged follow-up remains necessary to assess this approach in a more definitive way.

Epilepsy, Temporal Lobe↗

PubMed2002

[Gamma knife radiosurgery for the treatment of severe epilepsy].

The Gamma Knife radiosurgery is a neurosurgical approach having now demonstrated well its efficiency, its low morbidity and its comfort in the treatment of numerous neurosurgical disorders. These advantages of this type of intervention make it a method of great interest in functional neurosurgery and quite particularly in surgery of epilepsy. French experience is a pionner one in this domain. If for several years the positive evolution of the epilepsy associated to brain lesions had been noticed after the Gamma Knife radiosurgical treatment, the use of this approach in surgery of the epilepsy is systematically estimated since 1993. Data are today available concerning the surgical treatment of the epilepsies originating in temporomesiale area without occupying process, epilepsies associated to hypothalamic hamartomas and epilepsies associated to cavernous angiomas or to low grade gliomas. The quality of the epileptological result obtained in these various indications associated to a very reduced morbidity lets suppose that the Gamma Knife radiosurgery could indeed have tomorrow a place within the sample group of surgical approaches dedicated to the treatment of severe epilepsies. However, a larger number of treated patients and a more prolonged follow-up remains necessary to estimate in a more definitive way this approach.

Brain Diseases↗

PubMed2002

[The presurgical evaluation of epilepsies].

In this article, we present an overview of the principles, practices and procedures of the presurgical evaluation of the epilepsies in use in our center and in the majority of French teams. Surgery for epilepsy is offered to patients presenting with severe epilepsy with partial seizures. Its aim is to stop the seizures, or to significantly reduce their frequency. To do that, the epileptogenic zone should theoretically be removed and/or the propagation pathways of the seizures should be cut. Discussion of these indications inevitably includes prior assessment of the functional sequels (sensory, motor, cognitive or behavioral) which surgery is liable cause. The presurgical evaluation involves a multidisciplinary approach involving epileptologists, neurophysiologists, neuroradiologists, neuropsychologists and neurosurgeons and is carried out in two phases. The phase I is based on non-invasive investigations, including functional and structural neuroimaging, neuropsychological assessment, source localization of interictal spike and video-EEG recordings of seizures. The phase II is often required and is aimed to precisely define the anatomical localization of the epileptogenic zone and the relationships with a structural lesion. This invasive phase is mainly based on stereoelectroencephalography (SEEG). Finally, the surgical procedure must be adapted according to the distribution and dynamics of the anatomical and functional abnormalities which individually define each case of epilepsy.

Age Factors↗

PubMed2001

[Identification of epileptogenic networks from modeling and nonlinear analysis of SEEG signals].

This work is focused on the study of the organization of the epileptogenic zone (E.Z.) in humans based on the analysis of stereo-electroencephalographic (SEEG) signals with signal processing methods, and more especially those dedicated to the estimation of signal interdependencies. In order to evaluate quantities provided by these methods and in order to relate them to the notion of functional coupling between cerebral structures, we developed a neurophysiologically relevant model able to generate EEG signals from organized networks of neural populations. We showed that the model can produce realistic multichannel epileptiform signals (when compared to real SEEG signals) under certain conditions (excitation/inhibition ratio within populations, uni/bi-directional coupling between populations). In this paper, the model framework is used to evaluate the performances of nonlinear regression analysis as a method to characterize couplings between cerebral structures from the SEEG signals they produce. Two quantities, a nonlinear correlation coefficient and a direction index, respectively related to coupling parameters in the model (degree/direction) are presented. These two quantities are measured on real SEEG signals recorded in patients suffering from temporal lobe epilepsy and candidate to surgical treatment. Results show that the characterization of functional couplings leads to the identification of networks referred to as 'epileptogenic networks', which might be responsible for the triggering of seizures. These results also corroborate our previous results on the classification of temporal lobe epilepsies, showing that there exist recurrent seizure patterns that can be classified on the basis of interactions between medial and lateral neocortical structures.

Algorithms↗

PubMed2001

Interpretation of interdependencies in epileptic signals using a macroscopic physiological model of the EEG.

This paper presents a neurophysiologically relevant model in which vectorial epileptiform electroencephalographic (EEG) signals are produced from multiple coupled neural populations. This model is used to evaluate the performances of non-linear regression analysis as a method to characterize couplings between neural populations from EEG signals they produce. Two quantities, estimated on generated signals, namely the non-linear correlation coefficient and the direction index, are related to the degree and direction of coupling parameters of the model. Their statistical behavior is first studied on a set of signals simulated for relevant configurations of the model. They are then measured on real stereoelectroencephalographic (SEEG) signals. Results obtained in three patients suffering from temporal lobe epilepsy (TLE) show that abnormal functional couplings between cerebral structures, that establish during seizures, can be interpreted in terms of causality. Perspectives are oriented to the identification of epileptogenic networks in TLE.

Algorithms↗

PubMed2001

Neural networks involving the medial temporal structures in temporal lobe epilepsy.

OBJECTIVES: In a previous study using the averaged coherence technique to study interactions between medial/limbic and lateral/neocortical regions, we observed that epileptogenic networks in temporal lobe epilepsy seizures (TLES) could be divided into 4 subtypes, i.e. medial (M), medial-lateral (ML), lateral-medial (LM), and lateral (L). In the ML and LM subtypes, medial structures and the anterior temporal neocortex are co-activated at the onset of seizures. However, using this approach, we were unable to determine the direction of coupling and may have overlooked non-linear variations in interdependency. The purpose of the present study using non-linear regression for analysis of stereoelectroencephalographic (SEEG) signal pairs was to measure the degree and direction of coupling between medial and neocortical areas during TLES in patients with the M, ML, and LM subtypes. METHODS: Eighteen patients with drug-resistant TLEs who underwent SEEG recording were studied. We used a non-linear correlation method as a measure of the degree and the direction of coupling on SEEG signal pairs. Patients with pure lateral TLEs were not studied. We analyzed the functional coupling between 3 regions of the temporal lobe: the anterior temporal neocortex, the amygdala, and the anterior hippocampus. A physiological model of EEG generation was used to validate the non-linear quantification method and assess its applicability to real SEEG signals. RESULTS: Results are first based on a physiological model of EEG data in which both degree and direction of coupling are explicitly represented, thus allowing construction of the neural systems inside which causality relationships are controlled and generation of multichannel EEG signals from these systems. These signals provide an objective way of studying the performance of non-linear regression analysis on real signals. In medial networks (10 patients), the ictal discharge is limited to the medial limbic structures and may propagate secondarily to the cortex. Quantified results demonstrated no significant coupling between medial and lateral structures at the beginning of the seizures. Conversely, almost constant unidirectional or bidirectional coupling was observed between hippocampus and amygdala. In medial-lateral (5 patients) and lateral-medial (3 patients) networks, the initial ictal discharge includes both limbic and neocortical regions. A rapid "tonic" discharge is observed over the temporal neocortex at the onset of seizure. Quantitative analysis showed an initial increase in the non-linear correlation coefficient between neocortex and medial structures. Quantification of the coupling direction demonstrated influence of medial over lateral structures (medial-lateral) or of the lateral neocortex over medial structures (lateral-medial). CONCLUSIONS: These results confirm the existence of several generic and organized networks involving the medial structures during TLE seizures.

Amygdala↗

PubMed2001

Absence epilepsy with fast rhythmic discharges during sleep: an intermediary form of generalized epilepsy?

PURPOSE: To describe a particular form of absence epilepsy (AE) characterized by an atypical EEG pattern (fast rhythmic discharges) during sleep and an unfavorable course with the persistence of seizures at a late age and drug resistance. METHODS: We reviewed the medical files of 31 patients diagnosed with AE at our institution been 1995 and 1999 for whom an EEG during sleep had been recorded. Patients with fast rhythmic discharges during sleep were selected for the study. RESULTS: Five patients showed the usual criteria of childhood absence epilepsy (CAE) or juvenile absence epilepsy (JAE), but with fast discharges of rhythmic spikes (10-15 Hz) during sleep. such as those typically observed in Lennox-Gastaut syndrome. Four patients were of adult age at the time of the last examination. Intellectual capacities were "borderline" in each case, with visible social and learning handicaps. Absences were the initial seizure event in all patients, but four patients developed generalized tonic-clonic seizures during the course of the disease. Treatment using a combination of antiabsence drugs such as valproate and lamotrigine led to only marginal improvement. CONCLUSIONS: These findings illustrate the utility of sleep EEG in detecting the fast rhythmic discharges that are markers of drug resistance in AE and suggest the existence of transitional forms of AE that are intermediate between idiopathic and cryptogenic/symptomatic generalized epilepsies.

Adult↗

PubMed2001

Modeling EEG signals and interpreting measures of relationship during temporal-lobe seizures: an approach to the study of epileptogenic networks.

This work is focused on the study of the epileptogenic zone organization (EZ) in humans, based on the analysis of stereoelectroencephalographic (SEEG) signals with signal processing methods, and more specially those dedicated to the estimation of signal interdependencies. In order to evaluate quantities provided by these methods and in order to relate them to the notion of functional coupling between cerebral structures, we developed a neurophysiologically relevant model able to generate EEG signals from organized networks of neural populations. We showed [2, 3] that the model can produce realistic multichannel epileptiform signals (when compared to real SEEG signals) under certain conditions (excitation/inhibition ratio within populations, uni/bi-directional coupling between populations). In this paper, the model framework is used to evaluate the performance of nonlinear regression analysis as a method to characterize couplings between cerebral structures from SEEG signals they produce. Two quantities, a nonlinear correlation coefficient and a direction index, respectively related to coupling parameters in the model (degree/direction) are presented. These two quantities are measured on real SEEG signals recorded in patients suffering from temporal lobe epilepsy and candidate for surgical treatment. Results show that the characterization of functional couplings leads to the identification of networks referred to as "epileptogenic networks" and that might be responsible for the triggering of seizures. These results also corroborate our previous results on the classification of temporal lobe epilepsies [4, 5] showing that a recurrent seizure pattern exists that can be classified on the basis of interactions between medial and lateral neocortical structures. From the identified networks, it is also possible to describe "propagation networks" with a different organization is different and which play a major role in the clinical expression of seizures.

Journal Article↗

PubMed2000

Relevance of nonlinear lumped-parameter models in the analysis of depth-EEG epileptic signals.

In the field of epilepsy, the analysis of stereoelectroencephalographic (SEEG, intra-cerebral recording) signals with signal processing methods can help to better identify the epileptogenic zone, the area of the brain responsible for triggering seizures, and to better understand its organization. In order to evaluate these methods and to physiologically interpret the results they provide, we developed a model able to produce EEG signals from "organized" networks of neural populations. Starting from a neurophysiologically relevant model initially proposed by Lopes Da Silva et al. [Lopes da Silva FH, Hoek A, Smith H, Zetterberg LH (1974) Kybernetic 15: 27-37] and recently re-designed by Jansen et al. [Jansen BH, Zouridakis G, Brandt ME (1993) Biol Cybern 68: 275 283] the present study demonstrates that this model can be extended to generate spontaneous EEG signals from multiple coupled neural populations. Model parameters related to excitation, inhibition and coupling are then altered to produce epileptiform EEG signals. Results show that the qualitative behavior of the model is realistic; simulated signals resemble those recorded from different brain structures for both interictal and ictal activities. Possible exploitation of simulations in signal processing is illustrated through one example; statistical couplings between both simulated signals and real SEEG signals are estimated using nonlinear regression. Results are compared and show that, through the model, real SEEG signals can be interpreted with the aid of signal processing methods.

Cybernetics↗