Abstract
Recent work suggests that the default mode network (DMN) includes two core regions, the ventromedial prefrontal cortex and posterior cingulate cortex (PCC), and several unique subsystems that are functionally distinct. These include a medial temporal lobe (MTL) subsystem, active during remembering and future projection, and a dorsomedial prefrontal cortex (dmPFC) subsystem, active during self-reference. The PCC has been further subdivided into ventral (vPCC) and dorsal (dPCC) regions that are more strongly connected with the DMN and cognitive control networks, respectively. The goal of this study was to examine age differences in resting state functional connectivity within these subsystems. After applying a rigorous procedure to reduce the effects of head motion, we used a multivariate technique to identify both common and unique patterns of functional connectivity in the MTL vs. the dmPFC, and in vPCC vs. dPCC. All four areas had robust functional connectivity with other DMN regions, and each also showed distinct connectivity patterns in both age groups. Young and older adults had equivalent functional connectivity in the MTL subsystem. Older adults showed weaker connectivity in the vPCC and dmPFC subsystems, particularly with other DMN areas, but stronger connectivity than younger adults in the dPCC subsystem, which included areas involved in cognitive control. Our data provide evidence for distinct subsystems involving DMN nodes, which are maintained with age. Nevertheless, there are age differences in the strength of functional connectivity within these subsystems, supporting prior evidence that DMN connectivity is particularly vulnerable to age, whereas connectivity involving cognitive control regions is relatively maintained. These results suggest an age difference in the integrated activity among brain networks that can have implications for cognition in older adults.
Highlights
IntroductionThere has been growing interest in the default mode network (DMN), both as a set of regions active during spontaneous thought and less active during externally driven tasks (Shulman et al, 1997; Gusnard et al, 2001; Raichle et al, 2001), and as a functionally connected set of regions at rest and during task performance (Greicius et al, 2003; Fox et al, 2005; Buckner et al, 2008; Grigg and Grady, 2010a; Spreng and Grady, 2010; Allen et al, 2011)
The two distinct functional connectivity patterns identified by the medial temporal lobe (MTL) and dorsomedial PFC (dmPFC) analysis look similar to those identified by Andrews-Hanna et al (2010)
The two distinct functional connectivity patterns identified by the vPCC and dPCC analysis were similar to those identified by Leech et al (2011), and can be described as a stronger relation between the vPCC and the default mode network (DMN) on the one hand, and between the dPCC and task relevant regions on the other
Summary
There has been growing interest in the default mode network (DMN), both as a set of regions active during spontaneous thought and less active during externally driven tasks (Shulman et al, 1997; Gusnard et al, 2001; Raichle et al, 2001), and as a functionally connected set of regions at rest and during task performance (Greicius et al, 2003; Fox et al, 2005; Buckner et al, 2008; Grigg and Grady, 2010a; Spreng and Grady, 2010; Allen et al, 2011). One proposal that brings many of these aspects together (Buckner and Carroll, 2006) is that the DMN is involved in projecting the self through time (forward and backward), space (e.g., navigation) and into social situations involving others (theory of mind) This has appeal in attempting to explain the wide variety of processes that implicate the DMN, the central process mediated by the DMN remains elusive. These are the medial temporal lobe (MTL) subsystem, which is thought to underlie memory reconstruction and future projection (Schacter et al, 2007; Buckner et al, 2008), and the dorsomedial PFC (dmPFC) subsystem, which is thought to mediate self-referential thought more generally (Andrews-Hanna et al, 2010; Andrews-Hanna, 2012)
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