Washington (EurekAlert): A new neuroimaging study on stressed-out students suggests that male humans don't do their most agile thinking under stress. The findings, published this month in the Proceedings of the National Academy of Sciences, show that 20 male M.D. candidates in the middle of preparing for their board exams had a harder time shifting their attention from one task to another than other healthy young men who were not under the gun.

Previous experiments had found that stressed rats foraging for food had similar impairments and that those problems resulted from stress-induced changes in their brain anatomy.

The new study, using functional magnetic resonance imaging (fMRI) to scan the stressed students' brains, is a robust example of how basic research in an animal model can lead to high-tech investigations of the human brain.

"It's a great translational story," says Bruce S. McEwen, head of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology at The Rockefeller University, who worked on the project with colleagues at Weill Cornell Medical College. "The research in the rats led to the imaging work on people, and the results matched up remarkably well."

The work holds good news too, for both rats and humans: Their brains recuperate quickly. Less than a month after the stress goes away, they are back to normal. "The message is that healthy brains are remarkably resilient and plastic," McEwen says.

In earlier research on rats, neuroscientists found that these two tasks place demands on different circuits in the brain, and the circuits are affected in different ways by stress. In particular, collaborative work by McEwen and John Morrison at Mount Sinai Medical Center have shown that repeated stress on rats shriveled nerve cells of the medial prefrontal cortex, and that a shrunken prefrontal cortex is linked to slower performance on attention-shifting tasks.

The new research suggests that something very similar may happen to distressed humans. Liston, working with B.J. Casey at the Sackler Institute at Weill Cornell, used fMRI to explore his hunch that the brains of rats and men have some basic processes in common — that stress would also impair performance on attention-shifting tasks and diminish activity in the medial prefrontal cortex.