Poster E20, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
Using Concept Typicality to Explore the Semantic Neural Network in Healthy Ageing
Mara Alves1, Patrícia Figueiredo2, Ana Raposo1;1Faculdade de Psicologia, Universidade de Lisboa, 2Instituto Superior Técnico, Universidade de Lisboa
Richer semantic repositories foster more interconnected networks by increasing the links among disperse information. Therefore, the growth of the semantic knowledge along ageing may support the processing of concepts less well integrated in the semantic network, as is the case of atypical objects. However, progressive loss in executive functions in older ages may affect semantic control necessary for the appropriate processing of atypical concepts. In a previous study, we found that optimal ageing (indexed by age- and education-adjusted MoCA scores) supports the successful categorization of atypical concepts, whereas in suboptimal ageing the difficulties in categorizing atypical concepts re-emerged. Here, we investigate functional neuroimaging changes in the semantic network associated with age and explore differences between optimal and suboptimal ageing trajectories. In an event-related fMRI study, healthy young (n=14; age range=19-28) and older participants (n=15; age range=58-76) were presented with typical (e.g., apple) and atypical (e.g., avocado) objects of various categories (e.g., fruit) and were asked to silently name each object and then press a button. In the behavioural analyses a threshold of p<.05 was used. The two groups were matched in years of education, verbal semantic knowledge, tested using the WAIS Vocabulary subtest, and semantic association abilities, assessed by the Camel & Cactus test. General cognitive abilities of older adults were assessed through MoCA. Outside the scanner, all participants showed high accuracy in naming atypical and typical objects, with no differences in typicality or between groups. Inside the scanner, the button-press data revealed a typicality effect, with longer response times for atypical objects relative to typical ones, but no age-related differences. An FWE corrected cluster-level threshold of p<.05 was used in the neuroimaging analysis. In young participants, object naming recruited a widespread network, including bilateral lingual and fusiform gyrus, middle frontal gyrus, middle cingulate cortex and right precentral gyrus. In older adults, activation was restricted to object recognition areas, notably left inferior occipital gyrus and bilateral fusiform gyrus, extending more anteriorly in the right hemisphere to the inferior temporal cortex. The positive association between Vocabulary scores and activation in inferior temporal cortex indicates greater recruitment of semantic processes by older participants with richer semantic repositories. Moreover, suboptimal ageing (indexed by MoCA) was associated with a predominantly right-lateralized network, including fusiform gyrus, inferior temporal cortex and precentral gyrus. Importantly, the processing of atypical concepts involved different brain regions depending on age and cognitive ability. Young participants engaged bilateral middle occipital gyrus. Such activation was negatively associated with Vocabulary scores, suggesting that young adults rely on visual search to support increasing demands on object naming, especially in the absence of richer semantic repositories. In contrast, in suboptimal ageing there was increased recruitment of orbitofrontal cortex. Overall, these findings suggest that, despite of similar performance, the neural network supporting semantic abilities changes along ageing. Throughout the lifespan, object naming seems to rely more on the activation of semantic representations, but also becomes more dependent on the recruitment of frontal executive control processes when object identification is more demanding and general cognitive abilities decrease.
Themes: Meaning: Lexical Semantics, Control, Selection, and Executive Processes
Method: Functional Imaging