Title: Semantic but not sensory-motor neural routes are shared across language and action domains
Legend: Figure A – Compared to matched neurotypical (NT) participants, patients with left-hemisphere cerebrovascular accident (LCVA) imitated unnamed meaningful gestures more accurately than meaningless gestures. This finding suggests that semantic information was beneficial, whereas there was no added benefit of labeling/naming gestures. Figure B – Blue) Lesion associated with reduced benefit of semantic information on gesture accuracy. Red) Lesion associated with lower semantic memory performance on a non-gesture pictorial task. Magenta) Lesion to posterior temporal regions was associated with impairments in both language and action semantic domains.
Citation: Dresang, H. C., Wong, A. L., & Buxbaum, L. J. (2023). Shared and distinct routes in speech and gesture imitation: Evidence from stroke. Cortex, 162, 81–95. https://doi.org/10.1016/j.cortex.2023.01.010
Abstract: Dual-route models of high-level (praxis) actions distinguish between an “indirect” semantic route mediating meaningful gesture imitation, and a “direct” sensory-motor route mediates meaningless gesture imitation. Similarly, dual-route language models distinguish between an indirect route mediating production and repetition of words, and a direct route mediating non-word repetition. Although aphasia and limb apraxia frequently co-occur following left-hemisphere cerebrovascular accident (LCVA), it is unclear which aspects of these functional-neuroanatomic dual-route architectures are shared across praxis and language domains. This study focused on gesture imitation to test the hypothesis that semantic information (and portions of the indirect route) are shared across domains, whereas two distinct dorsal routes mediate sensory-motor mapping. Forty chronic LCVA and 17 neurotypical controls completed semantic memory and language tasks and imitated 3 types of gesture stimuli: (1) labeled/”named” meaningful, (2) unnamed meaningful, and (3) meaningless gestures. The comparison of accuracy between meaningless versus unnamed meaningful gestures examined the benefits of semantic information, while the comparison of unnamed meaningful versus named meaningful imitation examined additional benefits of linguistic cueing. Mixed-effects models examined group by task interaction effects on gesture ability. We found that for patients with LCVA, unnamed meaningful gestures were imitated more accurately than meaningless gestures, suggesting that semantic information was beneficial, but there was no benefit of labeling. Reduced benefit of semantic information on gesture accuracy was associated with lesions to inferior frontal and posterior temporal regions as well as semantic memory performance on a pictorial (non-gesture) task. In contrast, there was no relationship between meaningless gesture imitation and nonword repetition, indicating that measures of direct route performance are not associated across language and action. These results provide preliminary evidence that portions of the indirect semantic route are shared across the language and action domains, while two direct sensory-motor mapping routes mediate word repetition and gesture imitation.
About the Lab: Dr. Dresang’s research examines the cognitive and neural underpinnings of language, communication impairments, and treatments that can improve language following stroke, brain injury, and neurodegenerative conditions. Her research takes place at the Waisman Center, where she directs the Neuroscience of Language and Neurological Disorders “NeuroLAND” Lab.
Investigator: Haley Dresang, PhD