EMBARGOED UNTIL 11 A.M. PDT, AUG. 19, 1998
102-AD-98
Contact: Alicia Di Rado; (949) 824-6455; [email protected]
UC IRVINE NEUROSCIENTISTS TIE STRESS TO MEMORY LAPSES
Hormone Released During Acute Stress Appears to
Impair Memory Retrieval over a Specific Time Span
Irvine, Calif. - You study all week for tomorrow's big test. But minutes before the exam, your stomach is tied in knots. Then your mind goes blank when you see the test questions.
Neuroscientists at the University of California, Irvine, suspect they know why.
The hormone corticosterone, which is released during times of acute stress, appears to block the retrieval of long-term memories, with its effect peaking 30 minutes after a stressful incident, UC Irvine scientists write in the Aug. 19 edition of the journal Nature.
Dominique de Quervain and Benno Roozendaal, postdoctoral scientists at UCI, led the research investigating memory in rats in the laboratory of James McGaugh, director of the UCI Center for the Neurobiology of Learning and Memory. The researchers currently are conducting human experiments to confirm the rodent findings.
Their findings contribute to neuroscientists' understanding of the complicated ways in which memories are recalled, depending on our emotional and physical states. In addition, the research suggests new ideas about ways that hormones affect memory retrieval as well as formation.
It also expands knowledge of the survival behavior triggered by acute stress. "If you are in a stressful situation, it's not important to remember things like two plus two equals four-the most important thing is to run away," Roozendaal said.
Previous research using rats has shown that acute stress induces the release of corticosterone in test subjects. In human beings, a similar hormone called cortisol is released by the adrenal glands during acute stress. Previous research at UCI has found that corticosterone enhances the long-term storage of memories of stressful events.
Evidence from other laboratories already has indicated that long-term or chronic stress impairs the retrieval of memory. Now the new UCI study has shown that corticosterone released after a stressful incident can temporarily block the recall of long-term memories, with forgetfulness at its worst 30 minutes after the stress.
The researchers used young rats to test memory retrieval. They trained the rats to swim to a platform in a tank of water. Twenty-four hours after the rats learned to find the platform, the scientists stressed the rats by applying slight jolts to the rodents' feet-much like static electricity. When the rats were placed in the tank again 30 minutes later, they swam randomly without finding the target. But when rats were placed in the tank two minutes or four hours after the stress, they swam to the correct area of the tank.
The release of corticosterone appears to peak 30 minutes after a stressful incident, McGaugh said. Unstressed rats injected with corticosterone 30 minutes before being placed in the tanks showed forgetfulness, just like the stressed rats. Rats did perfectly well on the test if they were stressed but were given a drug that blocks the release of corticosterone.
In human beings, cortisol released by the adrenal glands normally fluctuates throughout the day, going from a peak in the morning hours to a dip at night. It has yet to be determined whether people retrieve memories more or less effectively depending on the timing of their natural body chemistry.
Future research at the Center for the Neurobiology of Learning and Memory will further explore the brain mechanisms involved in stress and long-term memory retrieval.
The UCI Center for the Neurobiology of Learning and Memory is an internationally known institute dedicated exclusively to the multidisciplinary investigation of how the brain processes information and makes and stores memories.
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