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Poster B22, Wednesday, November 8, 3:00 – 4:15 pm, Harborview and Loch Raven Ballrooms

Selective interference with sentence production by direct electrocortical stimulation of the inferior frontal gyrus

Edward F. Chang1, Garret Kurteff1, Stephen M. Wilson2;1University of California, San Francisco, 2Vanderbilt University Medical Center

Electrocortical stimulation mapping (ESM) has provided important insights into the neuroanatomy of language, due to its high spatial and temporal resolution, and the causal relationships that can be inferred from transient disruption of specific functions. Almost all ESM studies to date have focused on word level processes such as naming, comprehension and repetition. In this study, we used ESM to identify sites where stimulation interfered selectively with sentence production. Fourteen patients undergoing left hemisphere neurosurgery participated in the study. Significant expanses of perisylvian frontal, temporal and parietal regions were exposed in all participants. Patients were presented with pictures depicted a boy and a girl engaged in one of seven simple transitive actions (push, pull, hug, kiss, kick, chase, wash), and were asked to describe each picture using a simple sentence (e.g. “The boy is pushing the girl”) while stimulation was applied to a range of fronal, temporal and parietal sites. No patients had significant aphasia at baseline, and all were readily able to describe the pictures in the absence of cortical stimulation. Patients performed between 14 and 72 trials (mean 36.6 ± 13.7). When sites were found where stimulation interfered with sentence production, the same locations were stimulated again on later trials to establish reproducibility. We found sites were stimulation interfered with sentence production in a reproducible manner in eight out of fourteen patients. Nine sites were localized to the dorsal posterior inferior frontal gyrus (pars triangularis and opercularis), and none of these sites were implicated in any other language functions that were tested (counting, picture naming, repetition of single words). Interference with sentence production took several different forms, including mis-assignment of arguments to grammatical roles (“The boy is washing the boy”), omission of function words and inflectional morphology (“Girl is hug the boy”), misassignment of nouns to verb slots (“The girl is boying (.) is uh (.) pushing the boy”), and various paragrammatic constructions (“Uh (.) the girl (.) is (.) is (..) um (.) it was bathed she bathed him”). The remaining site was localized to the superior temporal gyrus, but it was not specific to sentence production; stimulation of this site also interfered with picture naming and repetition. Our findings suggest that the dorsal posterior inferior frontal gyrus is critically important for the generation of syntactic structure, since it was the only site where stimulation selectively interfered with sentence production.

Topic Area: Grammar: Syntax

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