Age differences in the intrinsic functional connectivity of default network subsystems

Campbell, Karen L.; Grigg, Omer; Saverino, Cristina; Churchill, Nathan W.; Grady, Cheryl L. · 2013 · OpenAlex-citations

DOI: 10.3389/fnagi.2013.00073

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Summary

This study investigates age-related differences in the intrinsic functional connectivity of specific subsystems within the default mode network (DMN). While the DMN is broadly associated with internally directed thought, recent evidence suggests it comprises distinct subsystems: a medial temporal lobe (MTL) subsystem linked to memory and future projection, a dorsomedial prefrontal cortex (dmPFC) subsystem involved in self-reference, and subdivisions of the posterior cingulate cortex (PCC) into ventral (vPCC) and dorsal (dPCC) regions. The vPCC is hypothesized to connect primarily with DMN regions, whereas the dPCC is thought to interface with cognitive control networks. The authors aimed to determine whether aging affects these subsystems differently, given prior findings that DMN connectivity generally declines with age while cognitive control networks are relatively preserved. The researchers analyzed resting-state fMRI data from 45 younger adults (mean age 22.4 years) and 39 older adults (mean age 69.0 years). To mitigate motion artifacts, a rigorous preprocessing pipeline was employed, including the removal of outlier time points identified through a multivariate analysis of motion parameters and fMRI signal intensity. The primary analytical method was seed-based partial least squares (PLS), a multivariate technique capable of identifying both common and unique patterns of whole-brain functional connectivity for multiple seed regions simultaneously. Two separate PLS analyses were conducted: one comparing the MTL and dmPFC seeds, and another comparing the vPCC and dPCC seeds. This approach allowed for the direct assessment of similarities and differences in connectivity patterns between these regions across age groups. The results confirmed the existence of distinct functional subsystems. Both the MTL and dmPFC shared a common network of DMN regions, but also exhibited unique connectivity patterns: the dmPFC connected with frontal and parietal regions, while the MTL connected with occipitoparietal areas. Similarly, the vPCC and dPCC shared common DMN connectivity but diverged in their unique connections; the vPCC connected exclusively with other DMN regions, whereas the dPCC connected with regions associated with cognitive control and salience networks. Regarding age differences, functional connectivity in the MTL subsystem remained equivalent between younger and older adults. In contrast, older adults showed significantly weaker connectivity in the dmPFC and vPCC subsystems. However, older adults demonstrated stronger connectivity in the dPCC subsystem compared to younger adults, particularly with cognitive control regions. These findings indicate that while the structural organization of DMN subsystems is maintained with age, the strength of functional connectivity varies by subsystem. The preservation of MTL connectivity and the enhanced dPCC connectivity in older adults support the hypothesis that connectivity involving cognitive control regions is relatively spared or upregulated during aging, whereas connectivity within core DMN subsystems (dmPFC and vPCC) is vulnerable to decline. This suggests an age-related shift in the integrated activity among brain networks, potentially reflecting compensatory mechanisms in older adults to maintain cognitive function despite reduced default mode network integrity.

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• executive function