Day after day of chronic stress will wear a person down physically and mentally. But new research suggests that the acute stress produced by a brief run-in with a stressful scenario acts on a key brain region controlling emotion and cognition, temporarily improving learning and memory.
Researchers at The Rockefeller University and the University at Buffalo have shown that acute stress in rats enhances certain brain functions through the effect of the stress hormone corticosterone (cortisol in humans) on the brain's prefrontal cortex. In research to be published online in the Proceedings of the National Academy of Sciences, they show that stress hormones increase transmission of the neurotransmitter glutamate and improve working memory.
"This study emphasizes that stress hormones like cortisol are beneficial to brain function in small pulses, even though they have a bad reputation when they act at high doses or over long time periods," says Bruce S. McEwen, head of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology at The Rockefeller University.
With Rockefeller postdoctoral fellow Ilia Karatsoreos and University at Buffalo collaborators, McEwen designed experiments to test the effect of acute stress on working memory. First, researchers trained rats in a maze until they could complete it correctly 60 to 70 percent of the time. When the rodents reached this level of accuracy for two days, half were put through a 20-minute forced swim - an acute stressor - and then were challenged with the maze again. The stressed rats made fewer mistakes as they went through the maze both four hours after the swim and one day post-stress, compared to the nonstressed rats.
To determine if the corticosterone neuropathway was responsible for the improved memory, as proposed, researchers injected one group of rats before the forced swim with a medicinal compound that blocks the action of the stress hormone, and injected another group with saline. Results showed that the saline group performed better in the maze than the blocked group.