Fig. 14. Positron emission tomography scans of three vertical slices through the brain revealed the areas of activation (whitened ) during administration of lists of words. In the unpracticed or naive subject (left column ), the anterior cingulate (top row ), temporal and frontal lobes (middle row ), and right cerebellum (bottom row ) are active, but the practiced subject performs the task with no activation of these areas (middle column ). Introduction of a new list of words reverses these practice-induced changes (right column ). (The reader should refer to the original reference for reviewing the colored pictures). From Posner and Raichle 196; used with permission.