Ageing manifests in various forms, notably through alterations in memory functions. Interestingly, the rate of memory decline isn’t uniform across all older individuals, with some experiencing a more rapid deterioration than others.
A team of psychologists from the University of Arizona embarked on a research project to understand the factors behind this variability. Their goal was to explore the circumstances that might cause memory to fade in some elderly individuals. The study paid close attention to factors that change with age and those that do not, affecting memory in both the young and the old.
Central to their findings is the role of the hippocampus, a brain area pivotal for memory and spatial navigation. The research suggests that difficulties some older adults face with learning new places and environments could be traced back to how neural representations are formed in the hippocampus. Li Zheng, the lead author and a research scientist in the Psychology Department, pointed out that these neural patterns might be why specific individuals struggle to recall locations.
Zheng highlighted the significance of these insights, especially for predicting memory decline in the initial stages of dementia. The study, now published in the Proceedings of the National Academy of Sciences, draws inspiration from a related investigation into rats by Carol Barnes, a distinguished professor with expertise in psychology, neurology, and neuroscience. Barnes’ research focused on “place cells” in the hippocampus, neurons that activate in specific locations, aiding in the mental mapping of spaces. This process, known as “remapping,” was less effective in older rats, indicating diminished spatial memory capabilities.
Building upon Barnes’ work, Zheng’s team experimented with 25 young and 22 older adults, all in good health. Participants engaged in a virtual reality task where they had to memorize the layouts of shops in two simulated towns. As they undertook this spatial memory test, their brain activity was monitored using functional magnetic resonance imaging, specifically looking at the hippocampus.
The findings confirmed that older adults generally showed less distinct neural representations of different environments than younger adults. However, the study also unveiled an age-independent factor influencing memory retention. According to Zheng, certain neurons in the hippocampus are specialized, with some responding to environmental shapes and others to colours or features. These neurons work together to form a complete ecological representation.
If neurons overlap in function, it might lead to inaccurate environmental representations, thereby lowering the fidelity of neural signals, explained Arne Ekstrom, a cognition and neural systems professor at the University of Arizona and a senior author of the study. The cause of these low-fidelity signals remains uncertain, but they are present in individuals with poor memory performance regardless of age.
The research also identified an age-dependent factor affecting memory: the quality of neural signals entering the hippocampus from other brain areas. The study observed that even high-performing older adults showed reduced quality in these incoming signals, which could be linked to changes in the brain’s plasticity as it ages. This decline in signal quality correlates with diminished spatial memory in older individuals.
These insights, particularly regarding the remapping index and signal fidelity, could be crucial in predicting the extent of memory decline in those with dementia. The research team is now looking to further this study through immersive virtual reality experiments, aiming to incorporate more naturalistic navigation cues and enhance our understanding of memory decline mechanisms in ageing populations.
More information: Li Zheng et al, Hippocampal contributions to novel spatial learning are both age-related and age-invariant, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2307884120
Journal information: Proceedings of the National Academy of Sciences Provided by University of Arizona
