An apparatus for detection of ANEA comprising an introducer having at least one lumen. The introducer is introduced into brain tissue through an opening in the skull. A reference electrode is positioned at an introducer distal portion. A plurality of electrode members are advanceable within the at least one lumen with each member having an insulated portion and an exposed distal portion. The members have a non-deployed state in the introducer and a deployed state when outwardly advanced out of the introducer. In the deployed state, the members are substantially orthogonal to each other with the exposed distal portions defining a detection volume capable of determining an electric field vector produced by the ANEA and the direction of foci of the ANEA.