An MRI study reveals that cortisol weakens grid cells, the specialized neurons that help us understand where we are. When landmarks are missing, the navigation system nearly stops working.
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 in the entorhinal cortex that function as part of the brain's internal GPS.
The finding comes from an imaging study involving 40 participants who completed a virtual navigation task while researchers monitored their brain activity with an MRI scanner. The results were published in PLOS Biology.
Each participant came in on two separate days. On one day, they received 20 milligrams of cortisol. On the other, they received a placebo. During both sessions, they navigated through a virtual meadow toward a series of trees. After reaching each tree, they had to determine the most direct route back to their starting position without being shown the correct path.
The researchers tested navigation under two conditions: one with no permanent landmarks, and one with a lighthouse as a fixed reference point.
Cortisol significantly reduced the participants' ability to orient themselves. Compared with their performance after the placebo, they made substantially larger errors when attempting to reach their destinations. This decline occurred regardless of whether landmarks were available or how complicated the route was.
The fMRI data showed the underlying mechanism. Under normal conditions, grid cells in the entorhinal cortex become active in a repeating grid pattern during spatial navigation. After cortisol, this grid-like activity became much less clearly defined. When participants navigated without permanent landmarks, the grid cell activity was almost entirely absent.
"Under stress, the brain loses the ability to effectively utilize its internal navigation maps," explained Dr. Osman Akan, lead author of the study.
Researchers also observed increased activity in the caudate nucleus after cortisol was administered, suggesting the brain attempts to rely on a different navigation strategy when its primary spatial mapping system is impaired.
The findings may also be relevant to Alzheimer's disease, because the entorhinal cortex is among the first brain regions affected by the condition. Chronic stress is a known risk factor for dementia, and this study reveals a specific mechanism for how stress hormones destabilize this sensitive region.