Aphasia, language disorder after acquired brain injury, is a chronic condition negatively impacting functional communication and quality of life. More than two million individuals in the United States have aphasia and the most common cause of aphasia is stroke. Further understanding of post-stroke aphasia will ultimately allow for development of more effective treatments for improved quality of life. Traditionally, characterization of aphasia both from a behavioral standpoint and in terms of task-based neural activation has focused on word-level tasks. However, everyday communication such as conversation and storytelling have discourse-level demands. As such, characterization of discourse in the post-stroke aphasia population will provide a more complete picture of functional communication impairment in this population.
Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique which uses the optical properties of hemoglobin to interrogate the hemodynamic response and task-based cortical activation. Unlike fMRI, fNIRS can be done sitting up in a clinic environment and is relatively less sensitive to motion artifacts. The current investigation uses fNIRS to evaluate cortical activity for three discourse production tasks in young neurotypical individuals, individuals with aphasia, and age-matched neurotypical individuals.
Experiment 1 evaluated cortical activity and behavioral response quality during a computer-based conversation task. Results of this experiment showed greater left frontotemporal cortical activity during the experimental condition (answering questions) as compared to a control condition (sentence repetition) in neurotypical individuals, suggestive of activation of a left-lateralized language network for this discourse-level formulation task. In addition, the young neurotypical group tended to show greater cortical activity when compared to the age-matched group.
Experiment 2 evaluated cortical activity and behavioral response quality during a computer-based narrative production task. Results of this experiment showed greater bilateral frontotemporal cortical activity during the experimental condition (narrative production) as compared to a control condition (counting aloud) across groups. Patterns of activity varied across groups in the temporal lobes, with an effect in the left hemisphere for the young and age-matched neurotypical individuals and in the right hemisphere for the age-matched group and individuals with aphasia. In addition, a measure of language production performance, global coherence, detected differences in behavioral responses between the young neurotypical group and individuals with aphasia in Experiments 1 and 2.
Experiment 3 evaluated cortical activity while answering conversational questions from a live interlocuter. Preliminary results of this experiment show greater cortical activity during the experimental condition (answering questions) as compared to the control condition (sentence repetition) in bilateral temporal ROIs across all three groups.
Taken together, these results suggest that a bilateral frontotemporal cortical language network supports discourse production, a cognitively complex task requiring the integration of phonological, lexical-semantic, morphosyntactic, and pragmatic information. Furthermore, results showed variable patterns between neurotypical individuals and individuals with aphasia. This work lays the foundation for future investigation of the cortical underpinnings of the various subcomponents of discourse as well as further characterization of cortical activity during ecologically valid functional communication tasks in individuals with aphasia.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/46602 |
| Date | 24 August 2023 |
| Creators | Braun, Emily Jane |
| Contributors | Kiran, Swathi |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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