A Common Neural Substrate for Language Production and Verbal Working Memory

摘要

Verbal working memory (VWM), the ability to maintain andnmanipulate representations of speech sounds over short periods,nis held by some influential models to be independent from thensystems responsible for language production and comprehensionn[e.g., Baddeley, A. D. Working memory, thought, and action.nNew York, NY: Oxford University Press, 2007]. We explore thenalternative hypothesis that maintenance in VWM is subservednby temporary activation of the language production systemn[Acheson, D. J., & MacDonald, M. C. Verbal working memorynand language production: Common approaches to the serial orderingnof verbal information. Psychological Bulletin, 135, 50–68,n2009b]. Specifically, we hypothesized that for stimuli lacking ansemantic representation (e.g., nonwords such as mun), maintenancenin VWM can be achieved by cycling information backnand forth between the stages of phonological encoding andnarticulatory planning. First, fMRI was used to identify regionsnassociated with two different stages of language production planning:nthe posterior superior temporal gyrus (pSTG) for phonologicalnencoding (critical for VWM of nonwords) and the middlentemporal gyrus (MTG) for lexical–semantic retrieval (not criticalnfor VWM of nonwords). Next, in the same subjects, these regionsnwere targeted with repetitive transcranial magnetic stimulationn(rTMS) during language production and VWM task performance.nResults showed that rTMS to the pSTG, but not the MTG, increasednerror rates on paced reading (a language production task)nand on delayed serial recall of nonwords (a test of VWM). Performancenon a lexical–semantic retrieval task (picture naming), inncontrast, was significantly sensitive to rTMS of the MTG. BecausenrTMS was guided by language production-related activity, thesenresults provide the first causal evidence that maintenance innVWM directly depends on the long-term representations and processesnused in speech production. ■