Summary: Researchers report that grid cell firing patterns become less stable with age, which may help explain why older adults often have more difficulty with spatial navigation than younger adults.
Source: DZNE
Researchers at the German Center for Neurodegenerative Diseases (DZNE) report a potential neural explanation for age-related declines in spatial orientation. In older adults they observed unstable activity in a brain region crucial for navigation, the entorhinal cortex. These findings, published in the journal Current Biology, may offer new leads for early detection of Alzheimer’s disease and for understanding age-related navigation problems.
The human brain synthesizes a wide range of signals to navigate effectively: visual input, proprioception, vestibular cues and motor feedback all combine to support spatial orientation. Navigation is therefore one of the most complex cognitive processes. Many people experience a gradual decline in these skills with age, and this decline can significantly reduce independence and quality of life.
“It is normal to get lost occasionally in unfamiliar surroundings, but older adults tend to experience this more frequently,” says Matthias Stangl, a researcher at the DZNE site in Magdeburg and first author of the study. “We know surprisingly little about the neuronal mechanisms behind these navigation difficulties. We hypothesized that grid cells, a critical component of the brain’s navigation system located in the entorhinal cortex, might be involved. Grid cells are thought to support internal computations of position and movement, so impairments in their function could contribute to age-related navigational deficits.”
In virtual reality and in real space
To test this idea, the team studied 41 healthy adults split into two age groups. The younger group included 20 participants aged 19 to 30, and the older group consisted of 21 participants aged 63 to 81; both groups included men and women.
The study combined two complementary experiments. In the first, participants navigated a computer-generated virtual environment while undergoing functional MRI (fMRI) to monitor brain activity. This allowed researchers to assess grid-cell-like representations in the entorhinal cortex during virtual navigation. The second experiment measured path integration ability: participants followed predefined curved routes and, at intermediate stops, estimated their distance and orientation relative to the starting point without being allowed to see it. This path integration task was performed in two versions, one in real physical space and the other in a virtual setting, to determine whether deficits were consistent across contexts.
Instabilities in firing patterns
“Overall, younger participants performed better on navigation tasks, which is consistent with prior research. Crucially, we found a link between poorer navigation and altered grid cell activity,” explains Prof. Thomas Wolbers, a senior DZNE scientist and supervisor of the study. “Grid-cell-like activity patterns were different in older adults: they showed reduced stability over time. This instability suggests that the neural circuits supporting spatial mapping are compromised in older age, which could underlie common navigational problems experienced by seniors.”
Wolbers adds that grid cells are important not only for navigation but also for other cognitive computations that rely on internal representations of space and movement. The observed loss of representational stability in entorhinal grid-cell-like activity therefore could point to a key mechanism underlying broader cognitive changes in aging. Understanding this mechanism may guide future strategies to counteract age-related cognitive decline.
An early sign for dementia?
While navigation difficulties can occur in healthy aging, impaired spatial orientation is also among the earliest signs reported in Alzheimer’s disease. “Assessing navigation performance together with measures of grid-cell-like function could potentially aid early diagnosis of Alzheimer’s and related neurodegenerative conditions,” says Wolbers. “However, effective diagnostic tools must be able to distinguish between normal age-related decline and pathology-driven changes, which is a challenging but important goal. Our results provide a foundation for further research aiming to separate healthy aging from early disease and to develop targeted diagnostic or therapeutic approaches.”
Study details: The research combined fMRI-based analysis of grid-cell-like representations in entorhinal cortex with behavioral path integration tests performed in both real and virtual spaces. Older adults showed reduced grid-cell-like representations, driven mainly by lower stability of these representations over time. Individual differences in grid-cell-like activity were associated with path integration performance: reduced grid-like signals correlated with larger navigation errors.
Implications: The findings suggest that compromised grid-cell function in the entorhinal cortex may be a key neural mechanism underlying age-related declines in spatial navigation. Because the entorhinal cortex is vulnerable to neurodegenerative changes in aging and Alzheimer’s disease, grid-cell instability might also serve as an early marker for disease processes, motivating further work on diagnostic differentiation and potential interventions.
Source: Marcus Neitzert, DZNE
Publisher: NeuroscienceNews.com (organized coverage)
Original research: Published in Current Biology (open access).
DOI: 10.1016/j.cub.2018.02.038
Abstract (rephrased)
Grid-cell-like representations in the human entorhinal cortex are compromised in healthy aging, mainly due to reduced representational stability over time. Older adults show impairments in path integration based on body-based and visual self-motion cues, and individual differences in grid-cell-like representations explain a portion of these path integration deficits. These results support the role of grid cells in path integration and suggest that impaired grid cell function contributes to age-related decline in spatial navigation and related cognitive functions.
Researchers emphasize that these findings are a step toward understanding neural changes that affect navigation in older adults and highlight the importance of further studies to translate these insights into diagnostic or therapeutic applications.