Sizable Declines in Associative Memory Occur by Age 50
Some aspects of cognitive function exhibit marked declines relatively early in later life, by middle age. Here, researchers show that episodic and associative memory recall, meaning the ability to correctly link together and place in context specific individual memories, shows a sizable decline in 50-something participants versus their 20-something counterparts. The fine details of the storage of memories are understood to be fairly dynamic over time; accessing memory can change storage, as can mechanisms of aging operating on the organization of neural networks. Even outside the context of aging, memory is far from perfect even in the best of circumstances. We forget most of our personal histories quite quickly, retaining perhaps 2% of the past according to early research into memory and forgetting. There is a great deal of room for improvement.
Episodic memory is the ability to bind elements of an experience into coherent associations. This ability declines with age, often producing errors that can interfere with daily life. Memory distortions might arise from unstable hippocampal representations that cannot be maintained across encoding, storage, and later retrieval. However, whether aging disrupts the temporal continuity of these representations across memory phases has not been directly tested.
Here, adults aged 20-74 completed functional magnetic resonance imaging (fMRI) scanning during an associative memory task involving face-object and face-scene pairings, followed by post-encoding rest and a cued retrieval test. Using multivoxel correlation structure analyses, we quantified hippocampal pattern similarity across each memory stage. Increasing age was associated with increased category errors and reduced representational similarity across all transitions. Higher encoding-retrieval similarity predicted better associative accuracy in younger adults and was less predictive in middle-aged and diminished in older adults.
Uniquely among older adults, greater cross-phase similarity predicted elevated category-level binding errors, suggesting a shift from selective reactivation to misbinding with age. Baseline hippocampal organization and encoding-specific connectivity supported accurate reinstatement only in younger adults. Thus aging disrupts hippocampal stability, possibly representing a core mechanism of age-related decline in associative memory across the adult lifespan.