A multi-electrode probe is used to create an electrophysiological depth profile during stereotactic neurosurgery. A surgeon uses CT or MRI images to identify the general location of a target site in the brain and then inserts the multi-electrode probe into this area. Each electrode on the probe produces a signal that indicates the level of activity in a nearby neuron or cluster of neurons. A processor converts these signals into an electrophysiological depth profile indicating the level of activity detected by each of the electrodes. The surgeon identifies the precise location of the target site by watching the display to determine which electrode or group of electrodes detects the highest level of neuronal activity as the stimulus is provided.