Electrode configuration for central nervous system monitoring

A method for positioning electrodes of an electrode array comprising not more than three measurement electrodes to identify, in an electroencephalographic (EEG) signal produced by the array, a period of time that is contaminated with artifacts resulting from eye movements of a subject, the method comprising steps of:

• positioning a first electrode of the array at a first location on a head of the subject and positioning a second electrode of the array at a second location on the head of the subject;
• obtaining an electroencephalographic (EEG) signal, the EEG signal comprising a voltage difference between a voltage obtained at the first electrode and a voltage obtained at the second electrode, wherein the locations of the first electrode and the second electrode are such that eye movement in a first direction selected from a group consisting of a horizontal direction and a vertical direction results in minimal change in the voltage difference, wherein the obtained EEG signal has minimal artifacts resulting from eye movement in the first direction;
• positioning a third electrode of the array at a third location on the head of the subject;
• obtaining an electrooculographic (EOG) signal comprising a voltage difference between a voltage obtained at the third electrode and the voltage obtained at the second electrode, wherein the location of the third electrode results in maximized voltage in the EOG signal as a result of eye movement in a second direction of the group consisting of the horizontal direction and the vertical dircction;
• and
• using the maximized voltage changes in the EOG signal to identify a time period in the EEG signal as an artifact contaminated time period resulting from eye movement in the second direction.

A method to minimize a number of electrodes in an array to only three by positioning electrodes of the electrode array to identify, in an electroencephalographic (EEG) signal obtained by the array, time periods that are contaminated with artifacts resulting from eye movements of a subject, the method comprising the steps of:

• positioning first and second electrodes of the array on a forehead of the subject at first and second locations at which the electrodes will obtain the EEG signal;
• obtaining the EEG signal by measuring a voltage difference between a voltage obtained at the first electrode and a voltage obtained at the second electrode, wherein the locations of the first and second electrodes are such that eye movement in one of a horizontal or a vertical direction will result in a minimal change in the voltage difference between the first electrode and the second electrode to provide the EEG signal in which artifacts resulting from eye movement in the one direction are minimized or eliminated;
• positioning a third electrode of the array on the head of the subject at a third location to maximize voltage changes occurring in an electrooculographic (EOG) signal as a result of eye movement in the other of the horizontal or the vertical direction;
• obtaining the EOG signal by measuring a voltage difference between a voltage obtained at the third electrode and a voltage obtained at an auxiliary electrode, wherein the auxiliary electrode is one of the electrodes in a set consisting of the first electrode and the second electrode;
• and
• identifying time periods in which the maximized voltage changes occur in the EOG signal as artifact contaminated time periods in the EEG signal wherein the maximized voltage changes result from eye movement in the other direction.