Stress does more than just put us on edge — it turns out it also weakens our senses.

A group of German researchers has found that the stress hormone cortisol blocks our senses’ ability to learn, in a test that involved sensory stimulation, according to a study in Psychoneuroendocrinology. Specifically, participants had their fingers stimulated and were tested to see how close to each other two sensations had to be before the people could no longer distinguish between them as separate stimuli — the point at which two sensations became one. The closer together that point was, the better their sense of touch.

When someone’s tactile perception improves during the test, that process signifies learning, the study says. But the neuroscientists treated half of their group with cortisol and found those people, as compared to those treated with a placebo, showed almost no improvement at all. The authors suggested that means stress blocks change in our brain’s sensory cortex.

Read: 6 Strange Things Stress Does to Your Body

“Previous research has already shown that stress can prevent the retrieval of memories,” Hubert Dinse, one of the authors of the study, said in a statement from Ruhr University Bochum. “But now we have discovered that it also has a major effect on our perception and perceptual learning.”

While the placebo group showed almost a 15 percent improvement in their sensory perception, a single 30 milligram dose of the stress hormone “completely blocked” improvement. Because cortisol is a key stress hormone in the human body, the researchers say their results suggest stress inhibits sensory learning.

That could be crucial information for people who are currently treated with corticosteroids, like those with immunological and neurological diseases. According to the university (link in German), that could affect those patients’ rehabilitation, which “rel[ies] on just these mechanisms” of sensory learning. “It is therefore necessary to find out which effects the clinical treatment ... has on learning mechanisms in the brain.”

Source: Wolf OT, Dinse HR, Kattenstroth JC, Lenz M and Tegenthoff M. The stress hormone cortisol blocks perceptual learning in humans. Psychoneuroendocrinology. 2017.

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