The functional relevance of dorsal motor systems for processing tool nouns- evidence from patients with focal lesions

This study asks whether lesions in different parts of the brain have different effects on the processing of words typically used to refer to objects with and without action affordances, for example tools and animal-related nouns. A cohort of neurological patients with focal lesions participated in a lexical decision paradigm where nouns semantically related to tools, foods and animals were presented along with matched pseudo-words. Differences in semantic features between the categories were confirmed using extensive semantic ratings whereas all semantic word categories were matched for relevant psycholinguistic variables. In a data-driven region of interest analysis, lesions in dorsal pre- and postcentral grey and white matter areas were associated to specific performance deficits for tool nouns when compared to animal nouns. In contrast, patients with lesions primarily affecting perisylvian inferior-frontal and/or temporal regions presented similar deficits across all semantic word categories tested and likewise a group of age and education matched healthy control participants did not show any category specific differences. These findings falsify brain language models denying the fronto-parietal cortex' role in word recognition and semantic understanding. They are best accounted for by frameworks that acknowledge a role of sensorimotor cortex in the semantic processing of action-related words.