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Accueil > Agenda > Les séminaires Jean Roche > Taxonomy of seizure dynamics and the virtual epileptic patient.

Taxonomy of seizure dynamics and the virtual epileptic (...)

Lundi 12 janvier 2015 - 11 heures.

Docteur Viktor JIRSA UMR S 1106, Institut de Neurosciences des Systèmes, Aix-Marseille Université..

Taxonomy of seizure dynamics and the virtual epileptic patient.

Résumé :

Seizures can occur spontaneously and in a recurrent manner, which defines epilepsy ; or they can be induced in a normal brain under a variety of conditions, in most neuronal networks and in most species from flies to humans. Such universality raises the possibility of the existence of invariant properties characterizing seizures in physiological and pathological conditions. Here, we analysed seizure dynamics mathematically and established a taxonomy of seizures based on bifurcation theory. For the predominant seizure class we developed a generic model called Epileptor. As an experimental model system, we used ictal-like discharges induced in vitro in mouse hippocampi. We show that only five state variables linked by integral-differential equations are sufficient to describe the onset, time-course and offset of ictal-like discharges as well as their recurrence. Two state variables are responsible for generating rapid discharges (fast time scale), two for spike and wave events (intermediate time scale) and one for the control of time course, including the alternation between “normal” and ictal periods (slow time scale). We propose that normal and ictal activities co-exist : a separatrix acts as barrier (or seizure threshold) between both states. Seizure onset is reached upon the collision of normal brain trajectories with the separatrix. We show theoretically and experimentally how a system can be pushed toward seizures under a wide variety of conditions. Within our experimental model the onset and offset of ictal-like discharges are well-defined mathematical events : a saddle node and homoclinic bifurcation, respectively. These bifurcations necessitate a baseline shift at onset and a logarithmic scaling of interspike intervals at offset. These predictions were not only confirmed in our in vitro experiments, but also for focal seizures recorded in different syndromes, brain regions, and species (humans and zebrafish). Finally, we identified several possible biophysical parameters contributing to the five state variables in our model system. We show that these parameters apply to specific experimental conditions and propose that there exists a wide array of possible biophysical mechanisms for seizure genesis, while preserving central invariant properties. Epileptor and the seizure taxonomy guide future modeling and provide the building blocks for the development of patient-specific brain networks. Here we present first results using The Virtual Brain platform (http://www.thevirtualbrain.org).

Invité par Dominique DEBANNE – UNIS UMR1072 - tél : 04 91 69 87 45.

Séminaire ouvert au public.

Nouvelle salle de conférence du secteur Nord de la Faculté de Médecine, rdc nord bâtiment E, 51 boulevard Pierre Dramard CS80011 - 13 344 Marseille cedex 15.

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