Dataset Information

Dissociating semantic and phonological contributions of the left inferior frontal gyrus to language production.

ABSTRACT: While the involvement of the left inferior frontal gyrus (IFG) in language production is undisputed, the role of specific subregions at different representational levels remains unclear. Some studies suggest a division of anterior and posterior regions for semantic and phonological processing, respectively. Crucially, evidence thus far only comes from correlative neuroimaging studies, but the functional relevance of the involvement of these subregions during a given task remains elusive. We applied repetitive transcranial magnetic stimulation (rTMS) over anterior and posterior IFG (aIFG/pIFG), and vertex as a control site, while participants performed a category member and a rhyme generation task. We found a functional-anatomical double dissociation between tasks and subregions. Naming latencies were significantly delayed in the semantic task when rTMS was applied to aIFG (relative to pIFG and vertex). In contrast, we observed a facilitation of naming latencies in the phonological task when rTMS was applied to pIFG (relative to aIFG and vertex). The results provide first causal evidence for the notion that anterior portions of the IFG are selectively recruited for semantic processing while posterior regions are functionally specific for phonological processing during word production. These findings shed light on the functional parcellation of the left IFG in language production.

SUBMITTER: Klaus J

PROVIDER: S-EPMC6916743 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Dissociating semantic and phonological contributions of the left inferior frontal gyrus to language production.

Klaus Jana J Hartwigsen Gesa G

Human brain mapping 20190410 11

While the involvement of the left inferior frontal gyrus (IFG) in language production is undisputed, the role of specific subregions at different representational levels remains unclear. Some studies suggest a division of anterior and posterior regions for semantic and phonological processing, respectively. Crucially, evidence thus far only comes from correlative neuroimaging studies, but the functional relevance of the involvement of these subregions during a given task remains elusive. We appl ...[more]

PMID: 30969004

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Project description:Previous lesion studies suggest that semantic and phonological fluency are differentially subserved by distinct brain regions in the left temporal and the left frontal cortex, respectively. However, as of yet, this often implied double dissociation has not been explicitly investigated due to mainly two reasons: (i) the lack of sufficiently large samples of brain-lesioned patients that underwent assessment of the two fluency variants and (ii) the lack of tools to assess interactions in factorial analyses of non-normally distributed behavioral data. In addition, previous studies did not control for task resource artifacts potentially introduced by the generally higher task difficulty of phonological compared to semantic fluency. We addressed these issues by task-difficulty adjusted assessment of semantic and phonological fluency in 85 chronic patients with ischemic stroke of the left middle cerebral artery. For classical region-based lesion-behavior mapping patients were grouped with respect to their primary lesion location. Building on the extension of the non-parametric Brunner-Munzel rank-order test to multi-factorial designs, ANOVA-type analyses revealed a significant two-way interaction for cue type (semantic vs. phonological) by lesion location (left temporal vs. left frontal vs. other as stroke control group). Subsequent contrast analyses further confirmed the proposed double dissociation by demonstrating that (i) compared to stroke controls, left temporal lesions led to significant impairments in semantic but not in phonological fluency, whereas left frontal lesions led to significant impairments in phonological but not in semantic fluency, and that (ii) patients with frontal lesions showed significantly poorer performance in phonological than in semantic fluency, whereas patients with temporal lesions showed significantly poorer performance in semantic than in phonological fluency. The anatomical specificity of these findings was further assessed in voxel-based lesion-behavior mapping analyses using the multi-factorial extension of the Brunner-Munzel test. Voxel-wise ANOVA-type analyses identified circumscribed parts of left inferior frontal gyrus and left superior and middle temporal gyrus that significantly double-dissociated with respect to their differential contribution to phonological and semantic fluency, respectively. Furthermore, a main effect of lesion with significant impairments in both fluency types was found in left inferior frontal regions adjacent to but not overlapping with those showing the differential effect for phonological fluency. The present study hence not only provides first explicit evidence for the anatomical double dissociation in verbal fluency at the group level but also clearly underlines that its formulation constitutes an oversimplification as parts of left frontal cortex appear to contribute to both semantic and phonological fluency.

Dataset Information

Dissociating semantic and phonological contributions of the left inferior frontal gyrus to language production.

Publications

Dissociating semantic and phonological contributions of the left inferior frontal gyrus to language production.

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