Dissociable Neural Mechanisms in the Default Mode Network Underlying Age-related Differences in Survival-related Memory Enhancement.

Memories encoded during survival situations are remembered more accurately than memories encoded during simple emotional situations. This enhancing effect of memory is known as survival-related memory enhancement (SME). SME has been consistently observed in young adults (YAs) and explained in the context of adaptive memory. However, little is known about the neural mechanisms underlying SME and how they are affected by aging. In the present fMRI study, we scanned healthy YAs and older adults (OAs) during encoding of objects when determining how the objects would be used in hypothetical survival situations. fMRI analyses focused on the default mode network subsystems (midline core [CORE], medial temporal lobe [MTL], and dorsomedial prefrontal cortex [dmPFC]). According to univariate analysis, regions in CORE and dmPFC showed significant activation during the imagination of survival situations in both YAs and OAs, whereas activation in regions of MTL was significant only in OAs. Multivariate pattern analysis demonstrated that in both YAs and OAs, activity patterns in CORE represented the information on self-other distinction and scene details in survival situations; the information on scene details was also represented in dmPFC. In addition, activity patterns in MTL represented the self-other distinction and survival scene details only in OAs. According to functional connectivity analysis, individual differences in SME of YAs were significantly associated with functional connectivity of the hippocampus with a region in dmPFC, whereas this functional connectivity was not identified in OAs. SME could be involved in the default mode network subsystems, and the roles of each subsystem in SME could be modulated by aging.