Door-to-door evangelists and yoga masters paint "stress" — and its evil cousin, anger — as enemies to human health and happiness, obstacles on the path toward enlightenment.

But researchers draw a distinction between chronic stress, etching lines in a face slowly fading into biology, and acute stress, the kind that helps an organism survive and even thrive in his or her environment.

In a new study, short bursts of acute stress proved beneficial as stem cells in the brain proliferated into new nerve cells that upon maturation improved mental performance. Such stimulus perhaps allowed laboratory rats to recall dangerous events in the future, said Daniela Kaufer, associate professor of integrative biology at the University of California at Berkeley, co-author of the research.

"You always think about stress as a really bad thing but it's not," she said. "Some amounts of stress are good to push you just to the level of optimal alertness, behavioral and cognitive performance."

Kaufer and co-author Elizabeth Kirby, a post-doctoral fellow there, determined how stress stimulates the brain for improved performance, publishing their results in the open-access journal eLife. "I think intermittent stressful events are probably what keep the brain more alert — and you perform better when you are alert," she said.

Bruce McEwen, who directs the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology at The Rockefeller University, said the research "reinforces the notion that stress hormones help an animal adapt — after all, remembering the place where something stressful happened is beneficial to deal with future situations in the same place."

Kaufer said she and her partner focused on the effects of stress on neural stem cells of the hippocampus, given that brain region's importance to memory. Depending on chemical triggers, such cells can mature into neurons, astrocytes or other brain cells, with the dentate gyrus of that brain region one of only two areas capable of generating new brain cells in adults. That particular area is also highly sensitive to glucocorticoid stress hormones, Kaufer said.

The astrocyte cells of the brain seem to play a key role in response to acute stress, with stress hormones stimulating these cells to release fibroblast factor grown, helping to create new neurons. In short bursts, the hormone stimulates the brain but with chronic stress the hormone suppresses new neuronal production in the hippocampus, harming memory and causing havoc throughout the body with an increased risk of chronic obesity, heart disease and depression.

While sometimes less is more, research studies to date have conflicted over the effect of acute stress on the brain. In the laboratory, Kaufer and Kirby subjected rats to acute stress by immobilizing them for a few hours, causing corticosterone stress hormone levels to rise. Within two weeks, the researchers discovered a doubling of the proliferation of new brain cells in the hippocampus, specifically in the dorsal dentate gyrus, correlating with improved performance on memory tests.

"In terms of survival, the nerve cell proliferation doesn't help you immediately after the stress, because it takes time for the cells to become mature, functioning neurons," Kaufer said. "But in the natural environment, where acute stress happens on a regular basis, it will keep the animal more alert, more attuned to the environment and to what actually is a threat or not a threat."

They also found that astrocytes appeared to play a larger role in regulating neurons, as the cells triggered the release of a protein, fibroblast growth factor 2, that helped nerve cell proliferation — pointing to possible treatment for depression, McEwen said, who was not involved in the research.

 "The FGF2 involvement is interesting, because FGF2 deficiency is associated with depressive-like behaviors in animals and is linked to depression in humans," he said.

The research provides an opening for more studies to determine the cost-benefit of particular responses to stress. "I think the ultimate message is an optimistic one," she concluded. "Stress can be something that makes you better, but it is a question of how much, how long and how you interpret or perceive it."

The researchers received funding from the National Institute of Mental Health and the National Alliance for Research on Schizophrenia and Depression, with Kirby receiving fellowship support from the California Institute for Regenerative Medicine and the U.S. Department of Defense.

The Centers for Disease Control and Prevention offer tips on managing stress.