(CNN) -- Memory loss during stressful situations can be blamed on an elevated level of a hormone affected by anxiety, researchers say.

They found that the rat hormone corticosterone -- when triggered in large amounts by stress, anxiety or even a physical blow to the body -- can block the retrieval of information stored in long-term memory. The study results were to be published in the journal Nature on Thursday.

Corticosterone is similar to cortisol, which is secreted under stress by the human adrenal gland, near the kidneys.

"There is a very selective time-dependent, memory-impairing effect of a stress hormone, and this time-dependency effect occurs one hour after the stress or the injection of the hormone," said James McGaugh, who directs the Center for the Neurobiology of Learning and Memory at the University of California at Irvine.

He said his research team is studying whether their findings also apply to humans, and is confident they do.

Researchers found that elevated levels of corticosterone, triggered by a small electric shock, crippled the ability of rats to find their way back to a designated target. The rats' memory was impaired most when hormone levels were at their highest -- about 30 minutes to an hour after the shock.

"This effect only lasts for a couple of hours, so that the impairing effect in this case is a temporary impairment of retrieval," McGaugh said. "The memory is not lost. It is just inaccessible or less accessible for a period of time."

So how do you remember the answers to an important test or the words to your wedding vows on the big day?

"When you are getting ready to take an exam, you might want to go and familiarize yourself with the location. You might study in the classroom you will take the exam in," suggested Eugia Littlejohn, a psychologist at Georgia State University.

Littlejohn also recommends some general stress-fighting techniques: Try slow, deep breathing, or close your eyes and envision a calm place.

Link: http://www.cnn.com/HEALTH/9808/19/stress.memory/index.html
News broadcast over CNN last August 19, 1998.