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Robust dissociation between the language and Multiple Demand networks in aging and after a stroke
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Poster E104 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Anne Billot1, Niharika Jhingan2, Maria Varkanitsa1, Isaac Falconer1, Nicole Carvalho1, Evelina Fedorenko2, Swathi Kiran1; 1Center for Brain Recovery, Boston University, Boston, MA, 2Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA
The human brain consists of functionally distinct large-scale networks (e.g., Yeo et al., 2011). A subset of these networks support high-level cognition and include the language network (Fedorenko et al., 2011) and the Multiple Demand (MD) network (Duncan, 2010). These two networks robustly dissociate in young adults (Fedorenko & Blank, 2020). However, some have argued that functional networks become less segregated with age (e.g., Chan et al., 2014) or after a brain injury (e.g., Siegel et al., 2016). We tested this hypothesis with respect to the language and MD networks for healthy older adults and adults with post-stroke aphasia, relative to young adults. 43 healthy older adults (age range:44-85), 24 adults with post-stroke aphasia (age range:18-81), and 568 young adults (age range:19-39) completed structural and functional MRI scans. The functional tasks included i) a language comprehension task (reading sentences vs. nonword lists), which reliably identifies the language-selective network (Fedorenko et al., 2010) and ii) a demanding non-linguistic task (a spatial working memory or an arithmetic addition task, including hard and easy conditions), which reliably identifies the Multiple Demand network (Fedorenko et al., 2013). Language and MD functional regions of interest (fROIs) were defined in each participant using a group-constrained subject-specific approach (Fedorenko et al., 2010). Within each parcel derived from probabilistic activation maps for the same contrasts in independent participants, a subject-specific fROI was defined as the 10% of voxels with the highest t-value for the relevant contrast. The magnitudes of response to the four conditions (Sentences, Nonwords, Hard, and Easy) were estimated in each fROI with a split-half approach to ensure independence of the data. The response magnitudes were examined using paired samples t-tests with FDR correction and compared among the three groups using linear mixed-effects models. The three groups exhibit some differences in the overall magnitude of response (patients show lower responses to language in the language network, and both older adults and patients show lower responses to MD tasks in the MD network). However, similar to previously reported findings in young adults (e.g., Mineroff et al., 2018) and replicated here, older adults and adults with aphasia show a robust dissociation between the language and the MD networks. In particular, the language fROIs show a language-selective profile with strong and reliable responses to the language task and little or no response to the MD tasks, whereas the MD fROIs show a strong and reliable response to the MD task (Hard>Easy), and most MD fROIs respond to the language task in the opposite way from the language network (nonword lists>sentences). The language-selective and the MD networks are robustly dissociated in their functional profiles not only in young adults, but also in older adults and adults with post-stroke aphasia. Identifying these networks in individual participants using extensively validated localizer tasks may be critical for uncovering these dissociations, as traditional group-averaging fMRI analyses do not take into account inter-individual variability in the precise locations of functional areas (and such variability may be even greater in aging or after brain damage).
Topic Areas: Control, Selection, and Executive Processes, Disorders: Acquired