Localizing interference during naming: Convergent neuroimaging and neuropsychological evidence for the function of Broca's area

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...

Distinct loci of lexical and semantic access deficits in aphasia: Evidence from voxel-based lesion-symptom mapping and diffusion tensor imaging

“…A number of neuropsychological studies demonstrate that patients with aphasia show exaggerated semantic interference when naming (Biegler et al, 2008;McCarthy & Kartsounis, 2000;Schnur, Schwartz, Brecher, & Hodgson, 2006;Schnur et al, 2009;Wilshire & McCarthy, 2002) and comprehending semantically related stimuli (Campanella, Crescentini, Mussoni, & Skrap, 2013;Forde & Humphreys, 1995Gardner et al, 2012;Jefferies et al, 2007; M A N U S C R I P T…”

“…Second, in the cyclical version of the blocked naming and word-picture matching paradigms, target items appear multiple times in different orders for a number of cycles (Biegler et al, 2008;Damian & Als, 2005;Schnur et al, 2006), where some patients demonstrate increasingly worse performance with repetition of related compared to unrelated target items (henceforth, increasing relatedness effect; Schnur et al, 2006Schnur et al, , 2009. Although repeating unrelated target items facilitates performance (i.e., repetition priming; e.g., Morton, 1969), this repetition priming is counteracted by interference when repeating target items belonging to the same semantic category (e.g., Oppenheim et al, 2010).…”

“…Although repeating unrelated target items facilitates performance (i.e., repetition priming; e.g., Morton, 1969), this repetition priming is counteracted by interference when repeating target items belonging to the same semantic category (e.g., Oppenheim et al, 2010). This is thought to reflect impairments in recruiting a cognitive control mechanism that comes online to resolve semantic interference which increases as related vs. unrelated target stimuli are repeated, at either a lexical (Biegler et al, 2008;Schnur et al, 2006Schnur et al, , 2009 and/or semantic level of representation . Consequently, poor performance in blocked-cyclic tasks is the result of damage to the representations themselves which creates noisy lexical or semantic activation (e.g., McCarthy & Kartsounis,…”

“…2000; Warrington & Cipolotti, 1996), and/or damage to a cognitive control mechanism involved in resolving interference (Biegler et al, 2008;Jefferies et al, 2007;Schnur et al, 2006Schnur et al, , 2009.…”

The neural substrates for atypical planning and execution of word production in stuttering

“…This discrepency may have resulted from the fact that previous studies did not separately examine planning and execution processes in which the left IFG may play different roles. Evidence on normal speech indicates that the left IFG is mainly involved in syllabification (Schuhmann et al, 2008) or phonetic encoding (Papoutsi et al, 2009), both of which are related to the internal construction of motor plan of speech acts (Moser et al, 2009;Schnur et al, 2009). Thus, our results not only confirmed the involvement of the left IFG in stuttering, but also strongly suggested a key role of the left IFG in atypical planning process in stuttering.…”