Hippocampal contributions to novel spatial learning are both age-related and age-invariant

Abstract

Older adults show declines in spatial memory, although the extent of these alterations is not uniform across the healthy older population. Here, we investigate the stability of neural representations for the same and different spatial environments in a sample of younger and older adults using high-resolution functional MRI of the medial temporal lobes. Older adults showed, on average, lower neural pattern similarity for retrieving the same environment and more variable neural patterns compared to young adults. We also found a positive association between spatial distance discrimination and the distinctiveness of neural patterns between environments. Our analyses suggested that one source for this association was the extent of informational connectivity to CA1 from other subfields, which was dependent on age, while another source was the fidelity of signals within CA1 itself, which was independent of age. Together, our findings suggest both age-dependent and independent neural contributions to spatial memory performance.

Spatial memory and hippocampal remapping: Who will age well?

“…Despite the ubiquity of this core skill, there are individual differences in spatial memory abilities, both at a young age and during healthy aging. In their paper in PNAS, Zheng et al ( 4 ), provide novel insights into the neural mechanisms underlying age-related cognitive decline in humans as well as a glimpse into why some individuals might be more resilient to these age-related declines.…”

“…The recent publication by Zheng et al ( 4 ) highlights two potential sources of spatial decline in older adults. The first is altered signal input into the CA1 region of the hippocampus, which was associated with age and mirrors the rodent literature.…”

“…Recent animal model studies of AD have reported deficits in remapping and reduced spatial precision of CA1 place cell firing patterns as potentially underlying spatial memory impairments in AD ( 21 , 22 ). Zheng et al’s ( 4 ) finding of reduced stability of neural activation patterns in the CA1 for the same environment in older adults provides novel insight into the neural mechanisms underlying spatial memory declines in healthy aging in humans. Indeed, these findings—and the overall methodology used in this study—provide a platform for future studies to investigate whether similar changes in CA1 could be tied to spatial memory impairments in people with AD, beyond that seen in normal aging.…”

“…Zheng et al’s ( 4 ) finding that individuals who performed better on spatial discrimination exhibited more distinct CA1 neural activation patterns for different environments—regardless of age—is particularly relevant for spatial memory training. If individuals with better spatial memory are better at differentiating between environments, then it is possible that improving this differentiation could strengthen the pathways for better memory.…”

“…Future studies could focus on training individuals to identify and remember defining features unique to different environments, like geometric cues ( 23 ) and salient landmarks ( 24 ). Such training could also help circumvent the age-dependent finding of Zheng et al ( 4 ) by increasing the quality of informational transfer into CA1 and contributing toward more differentiated representations in this region in older adults.…”