the invention relates to a method for positioning electrodes in an electrode array comprising a plurality of electrodes for central nervous system monitoring from the forehead of a subject . in order to enable efficient detection of eye movement artifacts with a minimum number of electrodes , first and second electrodes are positioned so that eye movement in one of the horizontal or vertical directions causes a negligible overall voltage change between the first and second electrodes and at least a third electrode is positioned so that eye movement in the other of said horizontal and vertical directions causes a high potential difference between the third electrode and an auxiliary electrode , wherein the auxiliary electrode is one of the electrodes in a set comprising one of the first and second electrodes and a fourth electrode . the first and second electrodes are arranged to record an eeg signal and the third electrode and the auxiliary electrode are arranged to record an eog signal indicative of eye movements of the subject .