Abstracts

The goal of this study is to analyze the variants of interaction of symmetrical mesiobasal epileptic foci in bitemporal intractable epilepsy patients verified by SEEG, intracranial recordings, and assessment of the surgical results. 129 intractable temporal lobe epilepsy patients (age range 6-53 year, duration of illness 3 -32 years) with bitemporal independent and synchronous in the multiple scalp EEG were studied. 117/129 patients were evaluated with implanted multiple deep and subdural electrodes at the Institute of Neurology, Tbilisi, Georgia. 12/129 patients were studied with bilateral subdural electrode grids implanted at the University of Chicago. Interelectrode coherence, power spectra, and frequency analysis were studied using the software package developed by one of us. Spectrograms of the recordings were used to identify various stages of seizure activity. 1) In patients with a clear epileptic focus in one temporal lobe the dormant symmetric epileptic focus could be detected in the EEG during the Wada-test. The results of surgery demonstrated that some failures are due to the activation of the contralateral focus verified with EEG/SEEG. 2) The mutually suppressive interaction of bilateral seizures was verified with decreasing of coherence, power spectra and spectrogram parameters in one epileptic focus during the increase of seizure intensity in the other. 3) The temporary local cooling of the deep epileptic focus with a cryosurgical device evoked a focal seizure in the symmetric structure. 4) Intensive focal epileptic discharge in the one deep foci lead to the suppression of activity in the contralateral focus and development of focal seizures during the postictal depression in the initiating focus. 5) Stimulation of the inactive, but verified epileptic focus (20-50 Hz, 1-2 mA, 0.2 ms, 2-3 s) during focal seizures in the symmetric focus lead to the development of afterdischarges in the stimulated structure, and termination of the first seizure. Applying the same parameters of stimulation to the first focus terminated the evoked seizure epileptic activity in both foci completely ceased. Our SEEG studies and analysis of the surgical results demonstrated that bitemporal epilepsy with clinically active unilateral foci is a more frequent pathology than is widely assumed (78/117, 66%). The inhibitory interrelations between deep temporal lobe foci may be used in future when the new generation of implantable brain stimulators developed.