A diagnosis of Alzheimer’s disease is currently dependent on an individual’s medical history, genetic risk factors, and performance on tests that measure memory, language, and reasoning impairments.
In a new review published in the journal Neuron, however, researchers suggest that navigational impairments such as how we sense our location and surroundings and give and follow directions, may be among the earliest signs of Alzheimer’s disease and could even lead to early diagnosis.
Unfortunately, age-related declines in navigational ability in both healthy individuals and in those with dementia have been understudied compared to aging’s effects on memory and learning.
“In humans, navigation is much more cumbersome to research than learning or memory,” said Dr. Thomas Wolbers, a neuroscientist specializing in aging and cognition at the German Center for Neurodegenerative Diseases.
“But it has such a dramatic impact on everyday life, and the key structures of the ‘navigational network’ in the brain are very sensitive to both ordinary healthy aging and pathological factors.”
Healthy older individuals, for example, strongly prefer to map objects and landmarks relative to their body position (an egocentric strategy) rather than in relation to external objects such as global landmarks or boundaries (an allocentric strategy).
This strategic bias makes it much more difficult for them to learn the spatial layout of an environment and can thus reduce their mobility, a worrisome sign in younger people.
Navigational testing is currently being held back by a couple of obstacles: The first is the lack of standard tests for navigational tasks and population norms with which to evaluate results. But more-affordable and portable virtual reality technology is in the works.
For example, study co-author Dr. Jan Wiener at Bournemouth University in the UK is one of the scientists behind the mobile app Sea Hero Quest, a game designed to collect population data on navigation decisions for dementia research.
The second obstacle is that navigational abilities vary widely from person to person, more so than for memory or other cognitive functions, Wolbers said. An effective diagnostic tool might need to be long-term and longitudinal, tracking an individual’s navigational skills at different points in time and looking for signs of early or accelerated decline.
“We need longitudinal human data to be able to definitively say whether a change in navigational function can be used to predict whether Alzheimer’s or any other neurodegenerative disease will develop later on,” Wolbers said.
“It can take up to 10 years after the onset of Alzheimer’s for someone to show abnormal results on the standard cognitive tests that are available today, and that’s 10 years that you’ve lost for treating it, should an effective therapy come along down the road,” he said. “This is where navigation-based diagnostics could contribute, by reducing that window.”
Once these obstacles have been overcome, the researchers conclude that a battery of navigational tests equivalent to those used for memory and learning will be possible. For now, Wolbers suggests that people train and use the navigational skills hardwired into their brains, especially in an age of GPS technology.
“There is growing evidence that if you rely too much on that technology it can have a detrimental effect on your navigational ability and in the long term may even be a risk to develop pathological conditions,” Wobers said.
Source: Cell Press