It's one of aging's many ironies: those who worry about getting
older may be hastening their own mental decline. Research shows that
stress makes the brain age more quickly and forget more readily.
The study, published in Nature Neuroscience, is the first to show
that cortisol, a hormone secreted in response to stress, can cause
healthy elderly adults to perform poorly on memory tasks. It appears to
do so by reducing the size of the hippocampus, a brain structure critical
to short-term and spatial learning.
Sonia Lupien, Ph.D, a neuroscientist at McGill University in
Canada, and her colleagues monitored a group of elderly people for five
years to examine the effects of cortisol on their brains. She found a
shrinking of the hippocampus in subjects who had higher, but still
normal, levels of cortisol, which continued to rise over the five-year
period. In subjects whose cortisol levels were normal and declined with
time, however, the hippocampus stayed the same size.
When asked to recall pictures of common objects or navigate a maze
seen the previous day—tasks that depend heavily on the hippocampus—the
high-cortisol group took longer than their low-cortisol
counterparts.
Those with impaired memories also reported feeling more stressed
than did other subjects. More crucial than the number of worries they
faced, says Lupien, was how they dealt with the pressures. People with
elevated cortisol levels, she contends, "are more reactive to their
environment"—and less in control of their troubles.
Neuroscientists now hope to determine the level at which cortisol
first begins to affect mental functioning. Observes Lupien: "We're at the
frontier of preventing pathological memory loss."
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