HIGH-SPATIAL-RESOLUTION EEG REVEALS DISTINCT INTERICTAL PATTERNS IN A RAT MODEL OF TEMPORAL LOBE EPILEPSY

Temporal lobe epilepsy (TLE) represents one of the most common forms of acquired drug-resistant epilepsy in adults. Despite their clinical relevance as a biomarker of seizure prediction, interictal events remain poorly characterised. The present study aims to investigate interictal patterns in an animal model of TLE using high-spatial-resolution EEG.
Sprague Dawley male rats (n=13) received pilocarpine intraperitoneally to induce status epilepticus. Two weeks later rats underwent surgical implantation of epidural and depth electrodes in several temporal lobe structures. Video-EEG was recorded and offline analysed. Experiments were performed in accordance with EU Directive 2010/63 and authorized by the Italian Ministry of Health.
We analysed 1.412 interictal events, which were categorised into 6 distinct patterns according to the classification used in the clinical setting: (i) spike (1,9%), (ii) polyspike (1,0%), (iii) burst (3,6%), (iv) brief potentially ictal rhythmic discharges (BIRDs; 16,6%), (v) highly epileptiform bursts (HEBs; 19,7%), and (vi) periodic discharges (57,2%). Data show that periodic discharges occur significantly more frequently than bursts, polyspikes and spikes (p<0.0001). The distribution of onset channels differed significantly across interictal event types (p<0.0001): periodic discharges originated in the vCA3 in roughly 50% of cases, whereas HEB events showed predominantly entorhinal cortical onsets.
Our findings demonstrate that high-spatial-resolution EEG allows a detailed characterization of interictal activity not previously achieved. The observed heterogeneity in the prevalence and features of interictal event types suggests that they may arise from distinct mechanisms and play different roles in seizure generation. Further studies are needed to elucidate the underlying processes.