Apparatus for use in a brain of a subject is provided, including an instrument, adapted to be inserted into the brain. A set of one or more electrodes, coupled to the instrument, are adapted to sense electrical activity of the brain and to transmit an electrical activity signal responsive thereto. A location sensor, adapted to be coupled to the instrument transmits a location signal indicative of a location of the instrument. A control unit, analyzes the electrical activity signal and the location signal. The control unit determines, responsive to the analysis, a position of the instrument with respect to an image of the brain, and electrophysiological information regarding tissue at the position.
