Summary: Overactive hippocampal activity may explain why some older people have trouble with spatial navigation and learning.
Too much activity in the hippocampus may cause navigation impairments seen in aging adults, according to new research published in Journal of Neuroscience.
Spatial navigation is one of the cognitive abilities that declines sharply in old age. Older adults often have difficulty navigating new environments and will choose to stick with familiar ones. Plus, key regions in the brain’s navigation circuit are some of the first affected by Alzheimer’s disease.
In a recent study, Diersch et al. examined the neural mechanism behind this decline in spatial learning.
In the study, younger and older adults (without known cognitive impairments) learned the layout of a town through virtual reality software. After touring the town, participants estimated the location of different landmarks while their brain activity was measured with fMRI. Most older adults did not perform as well as the younger adults and took longer to learn the layout of the town.
As the younger adults learned and their performance improved, activity in the hippocampus decreased while activity in other navigation areas increased. This pattern was not seen in older adults.
A failure to inhibit hippocampal activity could make brain signals too noisy, hindering spatial navigation performance.
Reducing hippocampal activity could become a treatment option for improving memory performance in aging adults.
About this neuroscience research news
Source: SfN Contact: Calli McMurray – SfN Image: The image is credited to Diersch et al., JNeurosci 2021
Increased Hippocampal Excitability and Altered Learning Dynamics Mediate Cognitive Mapping Deficits in Human Aging
Learning the spatial layout of a novel environment is associated with dynamic activity changes in the hippocampus and in medial parietal areas. With advancing age, the ability to learn spatial environments deteriorates substantially but the underlying neural mechanisms are not well understood.
Here, we report findings from a behavioral and a fMRI experiment where healthy human older and younger adults of either sex performed a spatial learning task in a photorealistic virtual environment. We modeled individual learning states using a Bayesian state-space model and found that activity in retrosplenial cortex/parieto-occipital sulcus and anterior hippocampus did not change systematically as a function learning in older compared to younger adults across repeated episodes in the environment.
Moreover, effective connectivity analyses revealed that the age-related learning deficits were linked to an increase in hippocampal excitability.
Together, these results provide novel insights into how human aging affects computations in the brain’s navigation system, highlighting the critical role of the hippocampus.
Key structures of the brain’s navigation circuit are particularly vulnerable to the deleterious consequences of aging, and declines in spatial navigation are among the earliest indicators for a progression from healthy aging to neurodegenerative diseases.
Our study is among the first to provide a mechanistic account about how physiological changes in the aging brain affect the formation of spatial knowledge. We show that neural activity in the aging hippocampus and medial parietal areas is decoupled from individual learning states across repeated episodes in a novel spatial environment.
Importantly, we find that increased excitability of the anterior hippocampus might constitute a potential neural mechanism for cognitive mapping deficits in old age.