Single-unit activities during epileptic discharges in the human hippocampal formation

Catalina Alvarado-Rojas (1) , Katia Lehongre (1) , Juliana Bagdasaryan (1) , Anatol Bragin (2) , Richard Staba (2) , Jérôme Engel Jr. (2) , Vincent Navarro (3, 1) , Michel Le van Quyen (1)

1 CRICM - Centre de Recherche de l'Institut du Cerveau et de la Moelle épinière
2 Department of Neurology [UCLA]
3 CHU Pitié-Salpêtrière [AP-HP]

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.

Domaines: Neurobiologie

Catalina Alvarado-Rojas, Katia Lehongre, Juliana Bagdasaryan, Anatol Bragin, Richard Staba, et al.. Single-unit activities during epileptic discharges in the human hippocampal formation. Frontiers in Computational Neuroscience, 2013, 7, pp.140. ⟨10.3389/fncom.2013.00140⟩. ⟨hal-01532111⟩