Abstract
Healthy aging is associated with brain changes that reflect an alteration to a functional unit in response to the available resources and architecture. Even before the onset of noticeable cognitive decline, the neural scaffolds underlying cognitive function undergo considerable change. Prior studies have suggested a disruption of the connectivity pattern within the “default-mode” network (DMN), and more specifically a disruption of the anterio-posterior connectivity. In this study, we explored the effects of aging on within-network connectivity of three DMN subnetworks: a posterior DMN (pDMN), an anterior DMN (aDMN), and a ventral DMN (vDMN); as well as between-network connectivity during resting-state. Using groupICA on 43 young and 43 older healthy adults, we showed a reduction of network co-activation in two of the DMN subnetworks (pDMN and aDMN) and demonstrated a difference in between-component connectivity levels. The older group exhibited more numerous high-correlation pairs (Pearson's rho > 0.3, Number of comp-pairs = 46) in comparison to the young group (Number of comp-pairs = 34), suggesting a more connected/less segregated cortical system. Moreover, three component-pairs exhibited statistically significant differences between the two populations. Visual areas V2–V1 and V2–V4 were more correlated in the older adults, while aDMN–pDMN correlation decreased with aging. The increase in the number of high-correlation component-pairs and the elevated correlation in the visual areas are consistent with the prior hypothesis that aging is associated with a reduction of functional segregation. However, the aDMN-pDMN dis-connectivity may be occurring under a different mechanism, a mechanism more related to a breakdown of structural integrity along the anterio-posterior axis.
Highlights
As our brain grows to maturity from childhood through adolescence and adulthood, it evolves to adapt to the ever changing external task demand and to its internal environment
Through the use of component analysis, we have presented an investigation of the subnetworks of the default-mode” network (DMN), finding that: (1) of the three isolated subnetworks of the DMN, two exhibited significant differences in network co-activation between the two population groups, and (2) the interaction between those two subnetworks may become interrupted with age
Reducing the assessment to the 31 overlapping high-correlation component-pairs, we found 3 component-pairs that were significantly different across the two population groups: V2–V1, V2–V4, and anterior DMN (aDMN)-posterior DMN (pDMN)
Summary
As our brain grows to maturity from childhood through adolescence and adulthood, it evolves to adapt to the ever changing external task demand and to its internal environment. Advanced aging is often associated with cognitive decline. Even before the appearance of noticeable decline in those abilities, the neural architecture underlying these processes has likely already undergone considerable change (Paulsen et al, 2004; Hampel et al, 2008; Callaghan et al, 2014). The “compensation related utilization of neural circuits hypothesis” (CRUNCH) posits that older adults may engage control at lower levels of task load to preserve performance, making age-related differences difficult to detect in behavioral measures where task load is lower than one’s cognitive limit despite large differences in underlying processing (Reuter-Lorenz and Lustig, 2005; ReuterLorenz and Cappell, 2008). Even when older adults do not show behavioral impairments, neural measures often indicate impaired or at least differential processing
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