We would like to thank S. Campbell for his invaluable help in preparing this manuscript. Thanks to W. Mayr for his time and effort in providing manual segmentation and K. Mueller for providing the volume rendering software and images of 3D brain visualizations. We have also benefited significantly from interactions with G. Wiet and D. Stredney. Volume datasets were provided by the Cancer Hospital Research Institute of the Ohio State University, the Alcohol and Drug Abuse Research Center at the McLean Hospital of the Harvard Medical School, and the National Library of Medicine. This work was supported in part by an ONR grant N00014-93-1-0335, an NSF grant IRI-9423312, an ONR Young Investigator Award (to DLW), and a DOD grant USAMRDC 94228001.