High levels of the stress hormone cortisol can temporarily impair memory, according to research published in the current issue of the Archives of General Psychiatry. The study suggests parts of the brain involved in memory may be demoted to a temporary "nonessential" status in times of severe stress.
Previous studies had shown that high doses of synthetic glucocorticoids, which are used as drugs to treat diseases like asthma and lupus, can cause brain damage and memory problems. Psychiatrist John Newcomer of Washington University in St. Louis decided to examine whether cortisol, a natural glucocorticoid that acts as a stress hormone, has the same effect at levels that can occur in the body. Cortisol helps jump-start the body's fight-or-flight response to stress by ordering more glucose to circulate in the blood.
Twice daily for 4 days, 51 healthy volunteers swallowed either a high dose of cortisol (160 mg), a lower dose (40 mg), or a placebo. The high dose "is not analogous to having a bad day at the office," says Newcomer; rather, it would be caused by things like undergoing major surgery, "marching 50 miles to a refugee camp during wartime, or having a terribly ill child," he says.
After one day, all volunteers performed equally well when asked to listen to and later recall paragraphs of text containing about 90 separate pieces of information. But after 4 days, 93% of individuals in the high-dosage group displayed a significant decrease in memory, recalling about 20 details fewer than those in the other groups. A week after the experiment, however, all subjects did equally well again. The researchers hypothesize that heightened levels of cortisol somehow prevent glucose transport into cells of the hippocampus, a brain structure known to play a role in memory, temporarily depriving them of energy in favor of other organs.
"It's noteworthy that the impairment didn't happen after a single episode," says neuroendocrinologist Bruce McEwen of Rockefeller University in New York City. "The brain is somewhat protected from stress since it doesn't show any effects immediately and these effects are completely reversible." Newcomer and his group would like to identify the specific cortisol blood level that begins to interfere with memory; they hope doctors can eventually use a blood test to rule out stress as a cause for memory problems in their patients.