Effects of aging on the mechanisms of dynamic integration between the default mode network and other brain networks: evidence based on fMRI data with natural stimulation.

Cognitive decline during aging affects daily life in older adults and is associated with altered functional connectivity (FC) between brain networks. However, the dynamic functional network connectivity (dFNC) alterations among brain networks in healthy older adults in response to natural stimuli are unclear. The present study included functional magnetic resonance imaging data of 217 healthy subjects from the Cambridge Centre for Aging and Neuroscience in the movie-watching state to analyze brain networks' dFNC and investigate the relationship between dynamic temporal metrics and cognition. Seven brain networks were obtained using independent component analysis. Four dFNC states were obtained in young and older groups, and connectivity between the salience network and the cerebellum decreased in state 3 in older adults compared to young adults. Older adults spent less time in the strong FC state 2, which was significantly associated with cognition, suggesting that integration across brain networks contributes to the execution of cognitive tasks. In conclusion, using a naturalistic viewing paradigm, this study provides novel evidence that healthy aging is associated with altered spatiotemporal dynamics of large-scale brain networks. Specifically, we identified reduced connectivity between the salience network and cerebellum in older adults and found that the diminished persistence of a key dFNC state (State 2) directly correlates with cognitive performance. These findings offer new insights into the neural mechanisms of cognitive aging by highlighting the critical role of dynamic inter-network integration.