1. Received March 3, 1998; revised July 24, 1998; accepted August 21, 1998. From the Departments of Neurology, Psychiatry and Nuclear Medicine, University of California at Los Angeles, West Los Angeles Veterans Affairs Medical Center, Los Angeles, California. Address correspondence to Dr. Mendez, Neurobehavior Unit (691/116AF), West Los Angeles VA Medical Center, 11301 Wilshire Boulevard, Los Angeles, CA 90073;