Abstract
Task-induced deactivations within the brain’s default mode network (DMN) are thought to reflect suppression of endogenous thought processes to support exogenous goal-directed task processes. Older adults are known to show reductions in deactivation of the DMN compared to younger adults. However, little is understood about the mechanisms contributing to functional dysregulation of the DMN in aging. Here, we explored the relationships between functional modulation of the DMN and age, task performance and white matter (WM) microstructure. Participants were 117 adults ranging from 25 to 83 years old who completed an fMRI task switching paradigm, including easy (single) and difficult (mixed) conditions, and underwent diffusion tensor imaging (DTI). The fMRI results revealed an age by condition interaction (β = −0.13, t = −3.16, p = 0.002) such that increasing age affected deactivation magnitude during the mixed condition (β = −0.29, t = −3.24 p = 0.002) but not the single condition (p = 0.58). Additionally, there was a WM by condition interaction (β = 0.10, t = 2.33, p = 0.02) such that decreasing WM microstructure affected deactivation magnitude during the mixed condition (β = 0.30, t = 3.42 p = 0.001) but not the single condition (p = 0.17). Critically, mediation analyses indicated that age-related reductions in WM microstructure accounted for the relationship between age and DMN deactivation in the more difficult mixed condition. These findings suggest that age-related declines in anatomical connectivity between DMN regions contribute to functional dysregulation within the DMN in older adults.
Highlights
Functional neuroimaging studies have demonstrated that some brain regions show lower activation during the performance of attention-demanding cognitive tasks compared to simpler baseline conditions (Shulman et al, 1997; Gusnard and Raichle, 2001; Raichle et al, 2001)
Indicated that fractional anisotropy (FA) was not related to default mode network (DMN) deactivation in the single condition (p = 0.13), but was significantly correlated in the mixed condition (β = 0.30, t = 3.42 p = 0.001)
There were marginal Age × Condition and Deactivation magnitude × Condition interactions for RT. Examination of these interactions (Figure 3) indicated that age was correlated with RT in both the single (β = 0.51, t = 6.38, p < 0.001) and mixed (β = 0.46, t = 5.62 p < 0.001) condition, while deactivation magnitude was correlated with RT in the mixed condition (β = −0.21, t = −2.32 p = 0.02) but not the single condition (p = 0.75)
Summary
Functional neuroimaging studies have demonstrated that some brain regions show lower activation during the performance of attention-demanding cognitive tasks compared to simpler baseline conditions (Shulman et al, 1997; Gusnard and Raichle, 2001; Raichle et al, 2001) Such task-induced deactivations tend to occur within the brain’s default mode network (DMN), which includes medial prefrontal cortex, posterior cingulate cortex/precuneus, White matter affects functional deactivation lateral portions of temporal and parieto-occipital cortices and hippocampus (HC) (Gusnard and Raichle, 2001; Raichle et al, 2001; McKiernan et al, 2003; Persson et al, 2007). Reduced deactivation of the DMN during task performance could be a significant contributor to older adult difficulties on attentiondemanding tasks
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