Brain and Cognition 44, 577–603 (2000) doi:10.1006/brcg.2000.1222, available online at http://www.idealibrary.com on Interhemispheric Effects of Simulated Lesions in a Neural Model of Letter Identification Natalia Shevtsova Kogan Research Institute, Rostov State University, Russia and James A. Reggia Departments of Computer Science and Neurology, Institute for Advanced Computer Studies, University of Maryland Published online August 15, 2000 Experimental studies have produced conflicting results about the extent to which the intact, nonlesioned cerebral hemisphere is responsible for recovery from cogni- tive deficits following focal brain damage such as a stroke. To obtain a better theoret- ical understanding of interhemispheric interactions during recovery, we examined the effects of simulated lesions to a bihemispheric neural model of letter identifica- tion under various assumptions about hemispheric asymmetries, corpus callosum influence, and lesion size. Among other results, the model demonstrates that the intact hemispheric region’s participation in the recovery process is a function of preexisting lateralization and lesion size, indicating that interpretation of experimen- tal work should take these factors into account.  2000 Academic Press INTRODUCTION When sudden focal damage occurs to the cerebral cortex, to what extent is subsequent recovery from cognitive deficits a local phenomenon in the lesioned hemisphere as opposed to compensation by the intact, contralateral hemisphere? Answering this question has long been of interest, not only due to its clinical relevance, but also for its implications concerning the nature of hemispheric interactions. For example, it is uncertain at present what un- derlying factors lead to lateralization of cognitive functions, whether such lateralization can shift dynamically following brain damage, and whether one hemisphere exerts predominantly an excitatory or inhibitory influence This work was supported by NINDS Awards NS35460 and NS29414. Address correspondence and reprint requests to James A. Reggia, Department of Computer Science, A. V. Williams Building, University of Maryland, College Park, MD 20742. E-mail: reggia@cs.umd.edu. 577 0278-2626/00 $35.00 Copyright  2000 by Academic Press All rights of reproduction in any form reserved.