Search for Functional Markers of the Hippocampus Involvement in the Pathological Process

— Electroencephalogram (EEG) patterns and the process of visual memory were studied in 27 patients with extracerebral tumors occupying mediobasal regions of the right and left hemispheres. The degree of involvement of the hippocampus (HP) in the pathological process was assessed based on neuroimaging (magnetic resonance imaging, MRI) and morphometric data. The predominant concentration of irritative–epileptiform signs in the affected hemisphere, as well as the presence of atypical α-rhythm episodes in the area of tumor projection, were treated as the EEG markers of tumor compressive effect on the HP. Signs of nonidentical involvement of the right and left HP in the pathological process were found in the form of the predominance of irritative signs in the left hemispheres of patients from the studied group as a whole. Equivalent dipole sources (EDSs) of atypical α-rhythm were more associated with the hippocampal structures compared to irritative EEG patterns. Neuropsychological testing of visual memory did not reveal considerable disturbances in memory processes at this stage of the disease.