Unprecedented levels of stress can cause disruptions in the thinking proceses of men, an American research team has found. The theory is based on the results of brain scans of 20 male medical students preparing for their board exams.
Bruce S. McEwen, head of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology at The Rockefeller University, revealed that the stressed students had a harder time shifting their attention from one task to another than other healthy young men who were not under the gun.
The researcher, who worked on the project with colleagues at Weill Cornell Medical College, says that the current study builds on a previous one that showed that stressed rats foraging for food had similar impairments, and that those problems resulted from stress-induced changes in their brain anatomy.
Writing about their work in the Proceedings of the National Academy of Sciences, the researchers revealed that they used functional magnetic resonance imaging (fMRI) to scan the stressed students' brains.
They said that their study was a robust example of how basic research in an animal model could lead to high-tech investigations of the human brain.
"It's a great translational story. The research in the rats led to the imaging work on people, and the results matched up remarkably well," says McEwen.
The study also revealed that the stressed brain recuperates quickly. It showed that less than a month after the stress goes away, the brains were back to normal.
"The message is that healthy brains are remarkably resilient and plastic," McEwen said.
During the study, the researchers scanned the brains of volunteers, some stressed and others relatively relaxed, performing two subtly different kinds of mental tasks, either an attention-shift or a response-reversal.
Lying inside the scanner, the subjects looked at two discs: one red and one green, with one moving up and the other down.
While undergoing a series of trials, the subjects were prompted to choose a disc according to motion or colour.
By ordering when the subjects did which tasks, they challenged their volunteers' brains to either switch focus from colour to motion, or to suddenly reverse their choice of a disc in the same category.
A previous collaborative study on rats has already shown that repeated stress on the animals shrivelled nerve cells of the medial prefrontal cortex, and that a shrunken prefrontal cortex is linked to slower performance on attention-shifting tasks.
Liston, working with B.J. Casey at the Sackler Institute at Weill Cornell, has revealed that male med students who said they were stressed out one month before they were to take their boards fared much worse on attention-shifting tasks than similar healthy adults who claimed to be taking it easy.
Finally, when Liston scanned the students again one month after the test, he discovered that their attention-shifting performance had returned to normal along with their brains.
Expressing surprise at the uncanny similarities, Liston said: "I certainly don't want to say that rat brains are just like human brains. But it does show that you can use research in animal models to help interpret human neuroimaging results."
Liston next plans to investigate how stress impacts the rest of the brain, and whether or not there are differences in how the brains of men and women respond to stress.
"Stress is doing a whole lot of things in your brain that we don't understand yet, but we know that it is intimately involved in a wide range of neuropsychiatric disorders," Liston says.
A mechanistic understanding of stress could lead to insights into associated psychiatric problems, he says.