Special Features of the Hippocampal Formation with Respect to Seizure Conditions

Abstract

The hippocampus has long been known as a region particularly prone to epileptiform discharges (Kandel et al. 1961). Connections and physiology of this archaic cortical structure are relatively well charac-terized and a wealth of information on features favoring exaggerated neuronal activity has emerged in recent years. The lamellar organization of the hippo-campus (Andersen et al. 1971) may be one of these features; it certainly has facilitated their investigation. Tissue slices cut along the lamellae, perpendicular to the axis of the structure, contain a relatively undisturbed chain of neurons which can be rigorously investigated in vitro. The results from such experiments have allowed modelling and imitation of hippocampal seizures on a computer (Traub et al. 1985). The properties of hippocampal neurons and their connections are discussed here successively for didactic reasons although they overlap functionally. Thus, the hallmark of epileptic activity, the paroxysmal depolarization shift (PDS), could equally well be considered a synaptic (Johnston and Brown 1981) or an intrinsic event (Schwartzkroin and Prince 1980).

This study was supported by the Swiss National Science Foundation (3.002.0.84) and Stiftung für Wissenschaftliche Forschung an der Universität Zürich.