Researchers discover intriguing new indicator of cognitive decline and dementia in older adults

Older people often show a decline in navigational ability, which is generally attributed to poorer spatial memory. But now, for the first time, US researchers have shown that this decline is partly caused by changes in typical exploratory behaviour in middle age. In a maze learning task, middle-aged people were less efficient explorers than younger people. This finding could have applications in the clinical diagnosis and therapy of cognitive decline and dementia.

Spatial navigation – the ability to select and follow a route from one place to another – is a skill we use every day. Depending on practice, general cognitive ability, and childhood environment, some people are naturally better at it than others. But research has also shown that people’s spatial navigation skills tend to decline as they age.

This decline in navigational skills is generally attributed to a decline in spatial memory, a result of changes in brain structure and function that naturally occur with age. But what if it’s not just because our spatial memory is declining, but also because of changes in the way we explore new environments? Such a shift has been observed in aging animals ranging from insects to rodents to fish.

And now, for the first time, an analogous shift in exploratory behavior in midlife has been demonstrated in humans. These results, which could eventually have clinical applications, are published in Frontiers in the neuroscience of aging.

An exploratory study

First author Dr Vaisakh Puthusseryppady, a postdoctoral researcher at the University of California, Irvine, said: “Compared with younger individuals, middle-aged individuals generally show less exploration when learning a new maze environment, and appear to prioritise learning specific key locations in the maze rather than the overall layout of the maze.”

Puthusseryppady and colleagues recruited 87 middle-aged (mean age 50) and 50 young (mean age 19) women and men as volunteers. None had a history of neurological disease, including dementia, or psychiatric disease.

Great groundbreaking research

The researchers tested how well the volunteers could explore and learn to navigate a maze in virtual reality. The maze consisted of intersections and corridors, separated by hedges. Recognizable objects were distributed at strategic locations as landmarks. In the first ‘exploration phase’ the volunteers were instructed to freely explore the maze and learn the locations of the objects.

In each of the 24 trials in the second ‘wayfinding phase’, the volunteers had to apply what they had learned and navigate between two randomly chosen objects within 45 seconds.

As expected, young people had a higher average success rate in finding their way. But more importantly, further statistical analyses showed that this difference in success rate was partly due to observed qualitative changes in how young versus middle-aged participants learned about the maze.

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“Compared to younger individuals, middle-aged individuals explored the maze environment less, as they traveled less distance, spent longer periods of time dwelling at decision points, and visited more objects than young individuals,” said Dr. Mary Hegarty, a professor in the Department of Psychological and Brain Sciences at the University of California, Santa Barbara, and a joint corresponding author.

These differences were so striking that the authors were able to use artificial intelligence to predict whether a participant was middle-aged or young.

Leading the way for applications

Reduced exploration in middle-aged people may result from age-related changes in the brain’s navigation network, for example in the medial temporal and parietal lobes.

The authors suggest that these findings may contribute to training interventions that can help middle-aged adults improve their navigation skills and maintain their cognitive abilities.

Co-author Daniela Cossio, a PhD candidate at the University of California, Irvine, explains: “If we were to train middle-aged people to better explore new environments – focusing on traveling longer distances, visiting paths that connect the environment, in a more distributed manner – this could lead to improvements in their spatial memory, which would help slow their decline in cognitive abilities.”

Dr. Elizabeth Chrastil, one of the corresponding authors and an associate professor at the same institute, looked ahead: “We are currently investigating whether these types of changes in exploratory behavior can be identified in people at risk for Alzheimer’s disease, as well as in people who actually have Alzheimer’s. We expect that altered exploratory behavior could eventually become a novel clinical marker for early cognitive decline related to Alzheimer’s.”

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