Analysis of decreased bioelectric activity of a brain with pharmacoresistant epilepsy

Abstract

High-frequency bioelectrical activity in pharmacoresistant epilepsy is analyzed. It has been established that pathologic high-frequency oscillations are a potential marker of the epileptogenic zone. We propose a classification of pathological high-frequency oscillations: 1) continuous high-frequency oscillations; 2) modulated pathological high-frequency oscillations, associated with slow waves; 3) modulated pathological high-frequency oscillations, associated with spikes. An example illustrating the application of the analysis of high-frequency bioelectrical activity for the localization of the epileptogenic zone in the widespread irritative zone is given. Variants of interrelation of the regions generating pathological high-frequency activity and epileptic activity in the range up to 70 Hz are demonstrated. Recording of epileptic activity in the frequency range up to 70 Hz is not an exclusive criterion of the epileptogenesis. Recording of modulated pathological high- frequency oscillations associated with spikes allows the differentiation of two spike types. We can assume that the mechanism for generating spikes containing high-frequency component differs from the one for plain spikes. The generators of the pathological high-frequency oscillations are characterized by a smaller size, which should allow more precise localization of the focus of pathological activity. In some cases, the analysis of the high-frequency component of the electrocorticogram makes it possible to differentiate the secondary irritative zone. It has been demonstrated that in patients with extratemporal, especially frontal, epileptogenic zone localization pathological high-frequency oscillations provide additional information about the location of the generator of abnormal activity.