title: Single-unit activities during epileptic discharges in the human hippocampal formation.
abstract: Between seizures the brain of patients with epilepsy generates pathological patterns of synchronous activity, designated as interictal epileptiform discharges (ID). Using microelectrodes in the hippocampal formations of 8 patients with drug-resistant temporal lobe epilepsy, we studied ID by simultaneously analyzing action potentials from individual neurons and the local field potentials (LFPs) generated by the surrounding neuronal network. We found that ~30% of the units increased their firing rate during ID and 40% showed a decrease during the post-ID period. Surprisingly, 30% of units showed either an increase or decrease in firing rates several hundred of milliseconds before the ID. In 4 patients, this pre-ID neuronal firing was correlated with field high-frequency oscillations at 40-120 Hz. Finally, we observed that only a very small subset of cells showed significant coincident firing before or during ID. Taken together, we suggested that, in contrast to traditional views, ID are generated by a sparse neuronal network and followed a heterogeneous synchronization process initiated over several hundreds of milliseconds before the paroxysmal discharges.
authors.affiliation: Centre de Recherche de l'Institut du Cerveau et de la Moelle Epinière, INSERM UMRS 975 - CNRS UMR 7225, Hôpital de la Pitié-Salpêtrière Paris, France ; Université Pierre et Marie Curie Paris, France.
authors.forename: Catalina
authors.initials: C
authors.lastname: Alvarado-Rojas
authors.forename: Katia
authors.initials: K
authors.lastname: Lehongre
authors.forename: Juliana
authors.initials: J
authors.lastname: Bagdasaryan
authors.forename: Anatol
authors.initials: A
authors.lastname: Bragin
authors.forename: Richard
authors.initials: R
authors.lastname: Staba
authors.forename: Jerome
authors.initials: J
authors.lastname: Engel
authors.forename: Vincent
authors.initials: V
authors.lastname: Navarro
authors.forename: Michel
authors.initials: M
authors.lastname: Le Van Quyen
keywords: interictal epileptiform discharges; microelectrode recordings; multiunit activity; spike synchronization; temporal lobe epilepsy