Post-stroke language difficulties (aphasia) are usually accompanied by impairments in working memory (WM), a cognitive system critical to daily functioning. WM plays an important role in language processing by temporarily storing and keeping information active for further processing. Post-stroke WM impairments have been suggested to affect language abilities and recovery in people with aphasia. However, the nature of the WM impairments in people with aphasia has remained controversial. Two mechanisms have been proposed for maintenance of information in verbal working memory (VWM): an articulatory rehearsal process relying on the interactions between left premotor and inferior parietal cortex, and a non-articulatory mechanism, the nature of which has remained controversial. The non-articulatory mechanism has been suggested to be an attentional process relying on the interactions of prefrontal attentional regions with WM stores in the brain. Our recent lesion-symptom mapping study on left-hemisphere stroke survivors showed that, depending on task demands, maintenance of verbal information relies on either auditory or articulatory brain regions. While lesions to the superior temporal gyrus disrupted performance under lower demands, suggesting reliance on auditory processes, lesions to sensorimotor cortex disrupted performance under higher demands suggesting reliance on articulatory rehearsal. Some deep white matter regions were also implicated in each task. These results clearly demonstrate a dissociation in the brain structures used for VWM maintenance under different task demands, but do not provide a complete picture of how strokes disrupt VWM. Since WM relies on a network of interconnected brain regions, VWM impairment likely results in part from structural disconnections and disrupted functional connectivity within the VWM network. However, the contributions of disconnections in VWM networks to VWM difficulties after left-hemisphere stroke has not previously been examined. This study of chronic left hemisphere stroke survivors with aphasia will identify the structural (Aim 1) and functional disconnections (Aim 2) underlying VWM deficits through integration of behavioral testing with structural connectome-symptom mapping and functional connectivity analyses (NIDCD Voice, Speech, and Language Program: Language mission areas). The main hypothesis is that post-stroke VWM impairments relate to structural disconnections and/or disrupted functional connectivity between bilateral prefrontal and inferior parietal regions, with a) auditory processing areas under lower task demands, and b) articulatory motor areas under higher task demands. Using data currently being collected in Dr. Turkeltaub?s lab, I will perform structural connectome-based lesion-symptom mapping and resting-state functional connectivity analyses to determine structural and functional disconnections that underlie VWM deficits. A knowledge of the cognitive and neural basis of post-stroke VWM impairments is crucial to understanding cognitive impairments in people with aphasia and may eventually lead to new treatments to improve language and other cognitive abilities.
Post-stroke language difficulties (aphasia) are usually accompanied by impairments in verbal working memory, a cognitive system responsible for temporarily storing and keeping verbal information active for further processing. This project aims to identify the functional and structural disruptions of brain networks that result in verbal working memory impairments in people with aphasia. This information is crucial to understanding verbal working memory difficulties faced by people with aphasia, and may eventually lead to new treatments to improve language and cognitive abilities.
