Feb. 27, 2023 -- You’re walking along a busy sidewalk, weaving through people, pets, and strollers, never colliding or losing your stride. How do you do that?
You can thank cells deep in your brain called grid cells, new research suggests.
Scientists have known that these cells help you track your movements, keeping tabs on where you’ve been, where you are, and where you’re headed, plus the direction of your gaze.
Now, using virtual reality and functional magnetic resonance imaging, or fMRI, researchers have discovered that they may help track the movements of those around us, too.
The study, published in Nature Communications, suggests that people may struggle to find their way around in spaces with lots of moving people if these brain cells lose the ability to function well.
The researchers from Austria, Israel, and the U.S. hope their findings will help explain why some people with age or dementia may become disoriented in crowds.
A Compass in Your Brain
Grid cells -- located near the bottom of the brain -- fire in distinctive hexagonal patterns, producing grid-like codes that map where you are in space relative to other people and objects.
This creates an "internal compass," the researchers say. It helps you get from point A to point B without bumping into anyone along the way.
"These signals might underlie our ability to make our way along a crowded sidewalk or to navigate towards a soccer goal by considering the position of the other team’s players," says lead study author Isabella Wagner, PhD, an assistant professor in cognitive neuroscience at the University of Vienna.
In the study, 60 healthy adults watched a computer screen while software recorded their eye movements and an fMRI monitored their brains. Each participant watched a computer-generated person walking in a virtual landscape. Then they assumed a first-person role in the virtual space and were asked to retrace the person’s path.
While the people in the study watched the person walking, and again while they retraced the path, their grid cells lit up. And while they tracked the other person, they also activated a network of related brain regions.
"We suggest that grid-like codes and their associated network dynamics could serve to distribute information about the location of others throughout the brain," the authors write. This “enables us to maneuver through crowded and dynamically changing environments as we encounter them in everyday situations.”
Interestingly, the people's whose grid cells lit up the most while observing the person were not as good at copying the path. That may seem surprising, but it also makes sense: The authors speculate that when brain cells work less efficiently, more cells and regions need to fire to get the job done.
"This seemingly counterintuitive result indicates that we still don’t fully understand the complex mechanisms by which the brain processes salient spatial information," says Vikram Rao, MD, PhD, a neurologist at the University of California San Francisco, who was not involved in the study.
Why This Matters: Aging, Alzheimer’s, and Epilepsy
Studying these navigation processes in healthy brains may help us understand why they sometimes break down.
"Impaired visual-spatial information processing can be an early sign of neurodegenerative diseases, such as Alzheimer’s,” says Rao. “Understanding how the brain normally processes this information may help us identify and lessen deficits in patients."
Wagner says in a news release that with age and dementia, grid cells become less effective.
"As a result, people can no longer find their way around and their orientation is impaired," she says.
The findings could shed light on epilepsy, too.
"In epilepsy, seizures commonly arise from the temporal lobe, which includes the entorhinal cortex," says Rao, division chief of UCSF’s Comprehensive Epilepsy Center. "This study advances our understanding of brain circuits that may be relevant in people with epilepsy."
Like all studies, this one had strengths and weaknesses.
The advantage of using fMRI, says Rao, is that it’s noninvasive and can “measure activity in all brain regions simultaneously."
But one drawback: That doesn’t tell us what the participants were thinking. While watching the virtual person move, some may also have been planning their own routes in advance, affecting the results, says Rao.
Next Steps
More research is needed before these findings can help doctors treat patients.
Wagner envisions follow-up studies “in elderly participants or in patients with dementia, to possibly develop a behavioral test or biomarker to detect warning signs as early as possible."
Her group is now exploring whether grid cells may help us recognize other people, an ability that can be impaired in advanced dementia.