[Optimal level of EEG coherence and its importance in evaluating the functional state of the human brain]

The study of EEG by means of computer analysis 46 healthy subjects and more than 100 patients with different disturbances of consciousness showed that one of the necessary conditions for performance of reactions to external stimuli and higher nervous activity consists in the maintainance of optimal level of coherence of brain electric processes, corresponding to the optimal cortical tone. Different depths of disturbances revealed different coherence deviations from the optimal level: its overall decrease in case of deep disturbances (coma), a sharp (pessimal) rise in the low frequency rang in sopor and within a wide frequency range in drowsiness in norm. The recovery of consciousness in the post-coma period and at early stages of coma is accompanied by a discordance between the levels of EEG coherence -- a decline in some cortical parts and a sharp rise -- in other ones.