stereotactic

At the beginning of the 20th century, neurosurgeons were experimenting with a technique used to direct the tip of a needle or an electrode in three spatial planes (length, width, and depth) to reach a particular place in the brain. At that time, the word for this technique was "stereotaxic," based on the prefix stereo- ("dealing with three dimensions of space") and "taxis" (referring to the manual restoration of a displaced body part). In 1950, "stereotactic" (based on tactic, meaning "of or relating to touch) joined the medical vocabulary as a synonym of "stereotaxic." Around the same time, a noninvasive neurosurgery technique was developed using beams of radiation. It is this procedure that is now often referred to by "stereotactic" and (less frequently) "stereotaxic."