Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2001.Includes bibliographical references (leaves 129-142).The Words-and-Rules theory (WR) posits that different mental processes underlie regular and irregular past tense formation: regular forms are rule-generated ('add -ed'), whereas irregular forms are retrieved from memory. These mental processes are hypothesized to engage distinct neural mechanisms. The goal of the present thesis was to localize and differentiate the neural substrates of regular and irregular past tense generation. Two neuroimaging techniques, magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) were used to test healthy, right-handed subjects who were native speakers of English in a past tense production paradigm, in addition to a lexical access study. The results indicate that there is a dissociation in both the time course of activation and brain areas involved for the regular vs. the irregular past tense formation.by Jaemin Rhee.Ph.D.