The relationship of bioelectric activity and structural changes in the hippocampus at pharmacoresistant temporal lobe epilepsy

Abstract

Background. Epilepsy is one of the most common neurological diseases globally. The unified concept about the role of hippocampus in the development of pharmacoresistant temporal lobe epilepsy is currently missing. Patients with pharmacoresistant temporal lobe epilepsy is often carried out by invasive electrocorticography to identify an epileptic focus. Registration of bioelectric activity of the hippocampus and comparison of data from the MRI pattern of the patient will determine the neurophysiological correlates of structural changes in hippocampus.Objective. The aim of the work was to determine the neurophysiological correlates of structural changes in the hippocampus in patients with focally caused temporal lobe epilepsy.Design and methods. The study was based on the analysis of the results of extraoperative invasive monitoring of the bioelectrical activity of the cortex and hippocampal complex, performed in 19 patients with focally caused drug-resistant epilepsy. The quantitative analysis included 34 tracks of hippocampal activity.Results. A distinctive feature of the bioelectrical activity of the hippocampal complex with its structural damage is the stable dominance of delta activity, which makes up 40–45 % of the total spectrum power. When the hippocampal complex is included in the epileptic system, high-index epileptiform activity is recorded. In the absence of structural damage to the hippocampal complex, the pattern is predominantly formed by the activity of theta and alpha frequency ranges. However, in the group of patients with the absence of a neuroimaging picture of sclerotic changes in the hippocampus, in 63 % of cases, a neurophysiological pattern of “prolapse” was recorded on the electrocorticogram. The spontaneous activity of the hippocampus had a low coherent relationship with the parameters of activity in the cortex of the ipsilateral and contralateral temporal lobes.Conclusions. The electrophysiological correlate of MR-positive structural changes in the hippocampal complex in drug-resistant epilepsy is the pattern of “loss of bioelectric activity”. Spontaneous hippocampal activity is generated independently of activity in the cortex of the ipsilateral and contralateral temporal lobes.

Epileptic Focus in Drug-Resistant Epilepsy: Structure, Organization, and Pathophysiology

“…When clinical and electroencephalographic data indicate possible involvement of the hippocampal complex in the epileptic system, invasive monitoring of the bioelectric activity of deep brain structures is performed: Spenser-type electrodes are installed stereotaxically in the basal and medial parts of the temporal cortex, in the hippocampus and amygdala, and less often in other structures. The choice of target structures is based on clinical picture analysis, scalp video EEG monitoring results, and ictal events semiology [12].…”