Abstract: An apparatus comprises a data processing unit, which causes the apparatus to: receive at least two electroencephalographic signals of a brain of a person; form a first information about at least one of the following: phase-to-phase coupling between at least two electroencephalographic signals, phase-to-amplitude coupling between at least two electroencephalographic signals and amplitude-to-phase coupling between at least two electroencephalographic signals, the first information being related to slow waves having frequencies at or lower than 1 Hz; normalize the first information; and output information about the normalized first information.

Abstract: An apparatus comprises a data processing unit (100) which receives electroencephalographic data based on a measurement of a person (110) exposed to anesthetic drug substance which has one or more estimated or measured non-zero levels of concentration in the body (108) of the person (110) as a function of time; and determines and present activity of slow waves of the electroencephalographic data at the one or more estimated or measured levels of the non-zero concentration of the anesthetic drug substance.

Abstract: An apparatus comprises a data processing unit and a stimulator. The data processing unit receives first electroencephalographic data based on a measurement of a brain of a person exposed to one or more estimated or measured non-zero amounts of anesthetic drug substance. The data processing unit performs a first comparison between the first electroencephalographic data and corresponding data of a reference brain function, and outputs information about the first comparison. The stimulator provides the brain of the person exposed to the anesthetic drug substance with brain stimulation on the basis of a direct or indirect reception of the information about the first comparison.