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Poster B55, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall

The multiple-demand network in language processing of the aging brain

Sandra Martin1,2,3, Dorothee Saur3, Gesa Hartwigsen1,2;1Lise Meitner Research Group “Cognition and Plasticity”, MPI for Human Cognitive and Brain Sciences, Leipzig, 2Research Group “Modulation of Language Networks”, Department of Neuropsychology, MPI for Human Cognitive and Brain Sciences, Leipzig, 3Language & Aphasia Laboratory, Department of Neurology, University of Leipzig

Normal aging leads to changes in neural networks of speech and language perception and production. Specifically, older adults commonly display less activation of domain-specific areas but a stronger involvement of the domain-general “multiple-demand” network in different tasks (Grady et al., 2010). This change in activation patterns appears to be especially robust when task demands increase and older adults show poorer behavioural performances in comparison to young adults (Hoffman & Morcom, 2018). A central question is to what extent language processing in the aging brain relies on domain-general versus domain-specific networks. So far, relatively few studies have investigated the interplay of these networks in language production in normal aging. In the current study, we used functional magnetic resonance imaging (fMRI) to characterize the role of the multiple demand network in an overt speech production task with varying task demands in healthy older adults. The data from twenty-eight older adults (mean age: 65.18 years, age range: 60-69 years) were included in the data analyses. Three additional participants had to be excluded from analyses due to heavy motion during scanning, i.e. motion parameters showed movement of more than one voxel size (2.5 mm) in any of the six directions. Participants performed two language production tasks during a continuous-sampling fMRI block design: semantic word generation (easy vs. difficult categories) and counting (forward and backward, control task). The semantic word generation task consisted of 20 categories that were assessed for difficulty during a pilot study in a separate sample of 24 older adults. The semantic word generation task was employed to engage both language and executive networks while the counting task served as a high-level baseline of a non-propositional, overlearned speech task. Behavioural results showed an effect of condition (semantic word generation vs. counting, Wilcoxon signed-rank test: Z = -12.65, p < .001) and difficulty (easy vs. difficult categories, Z = -9.76, p < .001), and an interaction between both factors. Whole brain fMRI analyses revealed different activity patterns for the semantic word generation task and the counting task (whole brain analyses, thresholded at FWE-corrected p < .05). Semantic word generation engaged distributed brain regions comprising frontal areas and the cerebellum when directly compared with the counting task. Notably, areas of the frontal network included domain-specific regions such as left inferior frontal gyrus as well as regions that have been associated with the multiple-demand network (Fedorenko et al., 2013) such as left supplementary motor area, bilateral middle frontal gyrus, left superior frontal gyrus, adjacent dorsal anterior cingulate cortex, and bilateral insulae. Areas that showed stronger activation for counting compared to semantic word generation consisted of bilateral precuneus and right anterior superior temporal gyrus which confirmed previous results on automatic speech tasks (e.g. Birn et al., 2010). The current study thus confirms evidence for an involvement of the multiple-demand network in a language production task with increased cognitive demand compared to an overlearned speech task. In the next step, we will use effective connectivity analyses to characterize functional interactions between domain-specific and domain-general regions.

Themes: Language Production, Control, Selection, and Executive Processes
Method: Functional Imaging

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