Decreasing Brain Functional Network Segregation with Healthy Aging
Date
2023-03-20
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Abstract
The functional architecture of the human brain consists of distinct sensory and associative functional networks that interact as needed. Resting-state functional magnetic resonance imaging (rs-fMRI) has shown that functional connections (connectivity) between networks strengthen with age, suggesting that networks reconfigure in healthy aging by becoming less segregated. Few studies, however, have replicated these findings or investigated sex differences in network organization, and no studies have thoroughly investigated if age-related differences involve certain networks more than others. It is crucial to better understand healthy age-related brain changes as it provides a foundation to better address and investigate age-related diseases like dementia or Alzheimer’s disease. In this thesis, cross-sectional functional and structural MR data from 231 presumed healthy adult participants (~59% self-reported as female, aged 18-91 y) from the Calgary Normative Study were examined to investigate the hypotheses that (1) whole-brain and network segregation decreases with age due to decreasing within-network and increasing between-network connectivity, and (2) age-associated increases in between-network functional connectivity occur in associative network connections. Structural and functional MR data were parcellated into seven known functional networks, and average within- and between-network connectivity were computed as the z-transformed Pearson cross-correlation coefficients (zw and zb, respectively). Whole-brain and network segregation were then computed using the segregation index, SI = (|zw|-|zb|)/(|zw|). All networks exhibited decreasing segregation with age, because of increasing between-network connectivity; however, within-network connectivity did not change with age. Further, between-network connectivity increased with age in sensory-to-associative and associative-to-associative network connections, as hypothesized. Increased connectivity between associative networks was also observed in males, regardless of age. This thesis demonstrates that functional networks reconfigure with age because of increased connectivity in sensory-to-associative and associative-to-associative network connections. This may constitute compensatory and/or de-differentiation processes as humans age. The findings of this thesis also provide a foundation for better interpretation of changes in brain function that occur in age-related diseases.
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Keywords
Functional Connectivity, Resting State Functional Magnetic Resonance Imaging, Healthy Brain Aging, Diagnostic Imaging
Citation
Singh Sidhu, A. (2023). Decreasing brain functional network segregation with healthy aging (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.