Times of dramatic progress in brain research have often been correlated with the development of new and powerful techniques that have changed the kinds of questions one can ask. An historical example may illustrate the point. More than 50 years ago, Nissl studies (Ferraro, 1928) showed that extensive forebrain lesions resulted in chromatolysis and cell loss in the sub- stantia nigra; thus, it was suggested that the substantia nigra gave rise to projections into the basal forebrain. In the late 1950s, another clue emerged, this time linking observations from the field of neuropathology with a...