Stability Of Default-Mode Network Activity In The Aging Brain

Abstract

Activity attributed to the default-mode occurs during the resting state and is thought to represent self-referential and other intrinsic processes. Although activity in default-associated regions changes across the lifespan, little is known about the stability of default-mode activity in the healthy aging brain. We investigated changes in rest-specific activity across an 8 year period in older participants in the Baltimore Longitudinal Study of Aging (BLSA) neuroimaging study. Comparison of resting-state and recognition memory PET regional cerebral blood flow conditions from baseline and 8-year follow-up shows relative stability of rest-specific activity over time in medial frontal/anterior cingulate, hippocampal and posterior cingulate regions commonly associated with the default-mode. In contrast, prefrontal, parahippocampal and occipital cortical regions, which are not typically associated with default-mode activity, show changes over time Overall, activity in the major components of the default-mode network remains stable in healthy older individuals, a finding which may assist in identifying factors that discriminate between normal and pathological aging.

Figure 1. Longitudinal Patterns of Default-Mode Activity

Legend: Top row illustrates default-mode regions commonly active during the resting state relative to task performance at years 1 and 9; these regions also show relative stability of rest-specific rCBF levels over time. Bottom row illustrates rest-specific regions that are active exclusively in years 1 or 9 and also show a significant increase (red) or decrease (blue) in resting-state relative to task-related rCBF levels over time.

Figure 2. Regions of Stable Longitudinal Activity

Legend: Average (SEM) blood flow values are shown for rest and task conditions at years 1 and 9. These examples show regions of no significant change in resting-state relative to task rCBF over time (p>0.14).

Figure 3. Regions of Decreasing Longitudinal Activity

Legend: Average (SEM) blood flow values are shown for rest and task conditions at years 1 and 9. These examples show declining resting-state rCBF over time (p values≤0.001) in conjunction with stable task-related rCBF, with the exception of the right parahippocampal gyrus (p=0.02). The apparent change in default-mode activity in this region is driven not by a decrease in resting rCBF but by an increase in task-related rCBF.