WEDNESDAY, April 12, 2006 (HealthDay News) -- The combination of a naturally occurring steroid hormone plus an emotional jolt seems to give memory a boost -- at least in rats.
The finding could give insight into therapies that might someday prop up fading memory in humans, the researchers said. It may also have implications for asthmatics and others who take a synthetic form of the glucocorticoid hormone, they added.
The role of glucocorticoids in memory has been known for some time, said Benno Roozendaal, an assistant researcher in neurobiology at the University of California, Irvine, and lead author of the study published in this week's issue of the Proceedings of the National Academy of Sciences.
He said this latest research suggests emotion is key to the hormone's memory-boosting effect.
Of course, "emotion" is defined differently in rats than in humans, Roozendaal said. All rats need for emotional arousal is to place them in a new environment, "a wooden box, a pretty boring box," he said. "But they are not used to that kind of box. It has an unfamiliar smell, so they are aroused by it."
All the rats in the study received injections of a glucocorticoid hormone called corticosterone. They were then tested to see if they could remember and recognize two objects 24 hours later.
The result: Rats placed in the arousing environment remembered the objects, but rats left undisturbed in their old cages did not.
Other experiments designed to explore the chemical basis of memory were based on the knowledge that a hormone called norepinephrine is involved in emotional arousal. When rats were given injections of norepinephrine, their memory appeared to improve when they also received corticosterone. But when they got injections of propanolol -- a chemical that blocks the activity of norepinephrine -- the scientists saw no memory boost.
So, what does all this mean for people?
"Glucocorticoids are fairly often prescribed to humans, for asthma and other conditions, so it is important to know under what conditions they might affect memory," Roozendaal said. "This study shows that they only have an effect at certain times."
He added that researchers developing drugs to boost memory in patients with Alzheimer's disease and other problems may want to keep the corticosterone-norepinephrine interaction in mind.
"This may be a general phenomenon," Roozendaal said. "It may be that every drug for memory requires this arousal, so drugs may be working in animals because they are using arousal. If they are given in humans, using boring information, they may not work. So, we would need to give the medication with something that causes arousal."
Research thus far has produced "some very general rules on how arousal has effects on memory," but much more is needed, Roozendaal said. "We really are interested in the reaction between brain regions," he said. "We are trying to see how different brain regions interact."
One expert said the new finding may turn some common wisdom on its head.
"The paper provides more precise information about a very interesting phenomenon," said Bruce S. McEwen, head of the laboratory of neuroendocrinology at Rockefeller University in New York City.
"Hence, although we may worry that stress makes us stupid, in actuality, the activation of stress hormones also enhances our memory of important things," he said.
More information
For more on memory and memory loss, head to the American Academy of Family Physicians.
