While stress may help your immune system, it apparently doesn’t do much for your memory. Animal studies have shown that long-term exposure to cortisol, a stress hormone released by the adrenal glands, kills memory- forming neurons. Now it seems that high cortisol levels have the same destructive effect in humans. Neuroscientists at Rockefeller University in New York and at two Canadian universities have found evidence that stress- related brain damage may explain why we often have trouble remembering things as we age.
Sonia Lupien at Rockefeller University and her colleagues at McGill University and the University of Montreal studied the effects of cortisol on 60 men and women over age 60. The researchers identified 15 people who secreted 50 percent more cortisol than other group members--and who secreted increasing amounts as they aged over the course of the five- year study. Cortisol, Lupien and her colleagues knew, serves a necessary function: when we face a threat, real or imagined, it raises blood pressure and signals the body to start breaking down stored energy reserves. But the researchers also knew that animals with high cortisol levels perform poorly in maze tests. So they decided to test four of their high-cortisol human subjects.
The researchers designed three mazes, two challenging, the other less so. For the first difficult maze, Lupien led her subjects through once and then had them try on their own. For the second, she didn’t lead them but told them in advance when to turn left and right. For the third and simpler maze, she gave them only a general description of the maze that would allow them to orient themselves and find their way out.
In the first two tests, which required good memories, the elderly with high cortisol levels did poorly. But in the third test--which required little memory but good spatial skills--they did as well as their peers with lower cortisol. Their problem, Lupien reasoned, wasn’t a lack of spatial orientation but memory loss--memory loss linked to their response to stress. When elderly people get lost, she says, it may be that they can’t remember what they need to find their way.