Characteristics of bioelectric activity in hippocampal region in drug-resistant mesial epilepsy

Abstract

Extraoperative invasive EEG-monitoring of bioelectric activity in cortical region and hippocampal complex may be performed in cases of discrepancy between clinical data, results of neurovisualization, and EEG-monitoring patterns when scheduling volume of surgical treatment in drug-resistant mesial epilepsy. A search for supplementary information about functional state of hippocampus may be directed to evaluation of its background bioelectric activity.The aim of our study was to characterize amplitude and frequency parameters of hippocampal bioelectric activity in mesial temporal epilepsy.Materials and methods. The study included analysis of amplitude and frequency parameters of background activity from the hippocampal complexes (21 tracks) performed during examination and surgical treatment of 17 patients (9 males and 8 females at the mean age of 31.5 years old) diagnosed with drug-resistant temporal mesial epilepsy. The two-year outcomes of selective amygdalae/ hippocampotomy in 7 patients were analyzed.Results. The interictal background bioelectric activity of structurally altered hippocampal complexes is characterized by dominating slow-wave activity. By their capacity, the hippocampal tracks may be classified in two groups: 1) high-amplitude activity reflecting the process of epileptogenesis; 2) low-amplitude activity which suggests a “burnout” of structurally impaired hippocampus. Analysis of clinical outcomes following amigdalae/hippocampotomy has shown that the favorable outcomes were significantly more frequent upon destruction of epileptized hippocampus. Conclusions. The specified variants of EEG-patterns may be regarded as neurophysiological correlates of pathogenetic mechanisms underlying the drug-resistant mesial epilepsy. Hyppocampal complexes with high-amplitude background activity represent pathological generators which are lost upon “burnout” of their activity.