Aging reduces shared event structure at encoding, weakening memory reinstatement in the Posterior Medial Network

Older adults often remember the gist of experiences but struggle with specific details. We show that this may reflect changes in how the brain processes events as they unfold. When younger and older adults watched the same television episode, older adults’ brain activity was less synchronized with others and showed greater individual variability within their age group. Critically, older adults with the strongest memory reinstatement showed encoding patterns that converged on shared event structure, with suggestive evidence that alignment with younger adults’ encoding patterns was especially important for bridging encoding and recall. This suggests successful aging may depend on preserving broader ways of representing events rather than following age-typical processing. Our findings reveal that memory decline reflects inconsistent encoding across individuals, not retrieval failure alone. It also suggests new avenues for detecting risk and improving memory as we age.