Changes in interictal spike features precede the onset of temporal lobe epilepsy.

Objective: One cornerstone event during epileptogenesis is the occurrence of the first spontaneous seizure (SZ1). It is therefore important to identify biomarkers of the network alterations leading to SZ1. In experimental models of temporal lobe epilepsy (TLE), interictal-like activity (ILA) precedes SZ1 by several days. The goal of this study was to determine whether ILA dynamics bore electrophysiological features signaling the impeding transition to SZ1.

Methods: Experimental TLE was triggered by pilocarpine- or kainic acid-induced status epilepticus (SE). Continuous electroencephalographic recordings were performed 7 days before and up to 40 days after SE. The amplitude and duration of the spike and wave components of interictal spikes were analyzed.

Results: Two types of interictal spikes were distinguished: type 1, with a spike followed by a long-lasting wave, and type 2, with a spike without wave. The number, amplitude, and duration of type 1 spikes started to decrease, whereas the number of type 2 spikes increased, several days before SZ1, reaching their minimum/maximum values just before SZ1.

Interpretation: The change in ILA pattern could constitute a predictive biomarker of SZ1. The mechanisms underlying these dynamic modifications and their functional impact are discussed in the context of the construction of an epileptogenic network.