No abstract

To produce a word, the intended word must be selected from a competing set of other words. In other domains where competition affects the selection process, the left inferior frontal gyrus (LIFG) responds to competition among incompatible representations. The aim of this study was to test whether the LIFG is necessary for resolution of competition in word production. Using a methodological approach applying the same rigorous analytic methods to neuropsychological data as is done with neuroimaging data, we compared brain activation patterns in normal speakers (using fMRI) with the results of lesion-deficit correlations in aphasic speakers who performed the same word production task designed to elicit competition during lexical selection. The degree of activation of the LIFG in normal speakers and damage to the LIFG in aphasic speakers was associated with performance on the production task. These convergent findings provide strong support for the hypothesis that the region of cortex commonly known as Broca's area (i.e., the posterior LIFG) serves to bias competitive interactions during language production. aphasia ͉ language production ͉ left inferior frontal gyrus ͉ lexical competition I n 1861, Paul Broca wrote ''somewhere in these [frontal] lobes, one or several convolutions holds under their dependence one of the elements essential to the complex phenomenon of speech.'' In the ensuing century and a half, investigations of the psychological and neural characterization of the ''phenomenon of speech'' have flourished. Here, we unite the principal method of Broca's day, the assessment of the relation between lesion location and cognitive impairments, with the primary human neuroscientific tool of the modern era, functional magnetic resonance imaging (fMRI), in a rigorous evaluation of one putative element of speech: conflict resolution.The need to resolve conflict during speech production is not self-evident; producing speech can feel spontaneous and easy. However, every word produced is susceptible to error. The analysis of speech errors, both the relatively infrequent ones that are made by normal speakers and those that occur with much greater frequency in patients with acquired language disorders, has been a rich source of information about the speech production process. Such analyses have revealed that word selection during production is a naturally competitive process, determined by the relative degree of support for (i.e., activation of) a set of candidate words (1-3). The question addressed in this article is whether a region of the frontal lobes commonly referred to as Broca's area [i.e., the posterior portion of the left inferior frontal gyrus (LIFG)], an area implicated in controlled memory retrieval (4), multiple aspects of language processing (5-8), and competition among linguistic and nonlinguistic representations (9, 10), is necessary for the resolution of conflict among competing lexical representations during word production. We posed this question of both normal and impaired speakers, using a word...