Stress can scramble your brain’s internal GPS, MRI study finds
The stress hormone cortisol can interfere with the brain system that helps people navigate and stay oriented. Researchers from Ruhr University Bochum in Germany found that cortisol weakens the activity of grid cells, specialized nerve cells that are essential for spatial navigation.
The finding comes from an imaging study involving 40 participants who completed a virtual navigation task while researchers monitored their brain activity with MRI. When participants were given cortisol before the experiment, they had more difficulty finding their way, and the normally precise activity patterns produced by grid cells became much less distinct. The findings were published in PLOS Biology.
Stress is already known to influence thinking and behavior, but researchers have had a limited understanding of how cortisol affects the specific brain circuits involved in navigation. Dr. Osman Akan from the Ruhr University Bochum, Department of Cognitive Psychology, worked with colleagues from the Department of Neuropsychology and researchers from University Hospital Hamburg-Eppendorf to examine this process more closely.
Testing Navigation Inside an MRI Scanner
The experiment included 40 healthy men who participated on two separate days. On one day, each participant received 20 milligrams of cortisol. On the other day, they received a placebo. During both sessions, they performed a spatial orientation task while their brain activity was recorded in an MRI scanner.
Participants navigated through a large virtual meadow and traveled toward a series of trees. Each tree disappeared once they reached it. Afterward, they had to determine the most direct route back to their original starting position without being shown the correct path.
Researchers tested navigation under two different conditions. In one version of the virtual environment, there were no permanent landmarks, and the trees served only as temporary destinations. In the other version, participants could use a lighthouse as a fixed reference point.
Cortisol Makes Navigation Less Accurate
The results showed that cortisol significantly reduced the participants' ability to orient themselves. Compared with their performance after receiving the placebo, they made substantially larger errors when attempting to reach their destinations.
This decline occurred regardless of whether spatial landmarks were available and regardless of how complicated the route was.
Stress Disrupts the Brain's Internal GPS
The effects of cortisol were also visible in the functional MRI data. Under normal conditions, certain nerve cells in the entorhinal cortex become active in a repeating grid pattern during spatial navigation. These cells are known as "grid cells" and effectively function as part of the brain's internal GPS system.
After participants received cortisol, this grid-like activity became much less clearly defined. The disruption was especially pronounced when participants navigated without permanent landmarks. Under those conditions, grid cell activity was almost entirely absent.
"Under stress, the brain loses the ability to effectively utilize its internal navigation maps," explains Akan.
Researchers also observed increased activity in another part of the brain called the caudate nucleus after cortisol was administered. This suggests that the brain may attempt to rely on a different navigation strategy when its primary spatial mapping system is impaired.
"This indicates that the brain is trying to compensate for the loss of the main navigation system in the entorhinal cortex through alternative strategies," says Akan.
Possible Relevance to Alzheimer's Disease
The findings may also be important for understanding Alzheimer's disease because the entorhinal cortex is among the first brain regions affected by the condition.
"Because chronic stress is a risk factor for dementia, our study reveals a critical mechanism for how stress hormones destabilize this sensitive region," explains Akan.
Reporting from ScienceDaily contributed to this story.
