A method concerning measurements by using an electrode array comprising three electrodes for central nervous system (CNS) monitoring from the forehead of a patient's head. A first electrode of said three electrodes is positioned between the eyebrows or immediately above the eyebrows of the patient. A third electrode of said three electrodes is positioned apart from the first electrode on the hairless fronto-lateral area of the forehead the patient. A second electrode is positioned between the first and the third electrodes on the forehead of the patient.