The role of brain segregation and integration in maintaining verbal fluency in healthy ageing – a secondary EEG data analysis

Ageing leads to word-finding difficulties, reflected in age-related decreases in verbal fluency. Further, verbal fluency might be an early marker for dementia. This study aimed to investigate the relationship between age-related decreases in verbal fluency and functional brain networks, specifically segregation and integration (i.e., communication between neighbouring and distant brain regions, respectively). We hypothesised that decreased network segregation is related to word-finding performance in older adults, but not in younger adults. The current secondary data analysis included 106 right-handed younger and older adults (N=53 per group) from the Leipzig Study for Mind-Body-Emotion Interactions (Babayan et al., 2019). The subset of participants used had no history of alcohol nor substance abuse, and no depression. Participants had completed a category and letter fluency task. We estimated functional networks from eyes-closed restingstate electroencephalography (EEG) recordings using the debiased weighted Phase Lag Index, filtered with the Orthogonal Minimum Spanning Tree algorithm. Segregation and integration were measured through the clustering coefficient (CC), modularity, path length (PL), and small-worldness (SW). Multiple linear regression analyses indicated that CC and modularity were positively related to letter fluency in the delta band. CC was negatively related to letter fluency in the alpha band and PL was positively related to letter fluency in the delta band. In the theta band, the effect of PL on letter fluency was greater in older adults. For category fluency, the effect of CC was lower in the beta band and higher in the delta band in older adults. These results indicate that segregation and integration are related to word-finding in older adults in a way that is specific to EEG frequency band. Therefore, maintaining word-finding in older adults may involve both short-and long-ranged brain connections. Babayan, A., Erbey, M., Kumral, D., Reinelt, J. D., Reiter, A. M. F., Röbbig, J., Schaare, H. L., Uhlig, M., Anwander, A., Bazin, P.-L., Horstmann, A., Lampe, L., Nikulin, V. V., Okon-Singer, H., Preusser, S., Pampel, A., Rohr, C. S., Sacher, J., Thöne-Otto, A., … Villringer, A. (2019). A mind-brain-body dataset of MRI, EEG, cognition, emotion, and peripheral physiology in young and old adults. Scientific Data, 6(1), 180308. https://doi.org/10.1038/sdata.2018.30