The aim of the study was to reveal changes in the brain's functional state of patients with apathic depression, aged 20-51 years, during the treatment. Spectral parameters of background EEG as well as latencies of simple sensorimotor reaction and of two-alternative choice reaction to auditory stimuli have been analyzed. The complex reorganization of EEG spatial-frequency structure at the stage of pronounced clinical improvement was noticed. It included the EEG signs of the facilitation of inhibitory processes (seen as the increase of slow wave delta, theta-1 and theta-2 spectral power) mainly in frontal, central and temporal areas of the right hemisphere; the EEG signs of decreased activation of temporal areas (seen as the decrease of beta spectral power mainly in the right hemisphere), as well as the EEG signs of increased activation of anterior cortical areas by excitatory brain stem reticular structures (seen as the increase of beta spectral power in left frontal and central zones). The mean values of latencies of both simple sensorimotor reaction and of two-alternative choice reaction have been decreased as well. The data obtained are in line with contemporary views on the predominant role of the right hemisphere in the regulation of negative emotions and in the pathogenesis of depression.