NEUROSCIENCE Edited by DALE PURVES GEORGE J. AUGUSTINE DAVID FITZPATRICK WILLIAM C. HALL ANTHONY-SAMUEL LAMANTIA JAMES O. MCNAMARA S MARK WILLIAMS Sinauer associates, Inc. Publishers Sunderland, Massachusetts U.S.AEdited by DALE PURVES GEORGE J. AUGUSTINE DAVID FITZPATRICK WILLIAM C. HALL ANTHONY-SAMUEL LAMANTIA JAMES O. MCNAMARA S. MARK WILLIAMS NEUROSCIENCE THIRD EDITION Sinauer Associates, Inc. • Publishers Sunderland, Massachusetts U.S.A. Purves3/eFM 5/13/04 12:59 PM Page iii