Then, on a hunch, Cahill’s lab decided to take a closer look at how sex differences might play a role in this long-established “safe general rule” and, surprisingly, discovered in one experiment that the rule did not apply to women. In that experiment, Cahill tested the memories of both men and women after an acute stress and found that the stressful event enhanced the memories of the men but did not do so for the women. (Yes, Denise Carleton’s killer recall seems to contradict this, but stay with us.) It was a puzzling finding: The levels of stress hormones were elevated equally in both males and females–so why didn’t it have the same affect on their memories?
Thinking that perhaps stress hormones were interacting with sex hormones, they ran the experiment again, this time using only women and controlling for various phases of the menstrual cycle. They discovered that when women had high levels of estrogen (before and during their periods), stress fuzzed up their recollection, but when they had high levels of progesterone, following their cycle, stress boosted recall–just like it did for guys. In other words, women received the memory lift that acute stress provides only when their estrogen levels were normal.
Cahill’s work was groundbreaking–and goes a long way toward explaining Denise’s peak performance in the doctor’s office (she was in that high-progesterone part of her cycle). It also explains why, on other days when she’s been pelted with curveballs, she’s been known to forget that she tossed her cell phone on the bumper of her truck or left a takeout pizza on the roof.
“Most of the research on stress and memory has been done in adult male humans, rats, and monkeys,” says Victoria Luine, Ph.D., a neuroendocrinologist at Hunter College in New York City, whose own work has since revealed similar findings. “Scientists have taken the male model and just assumed that females are the same. It’s a big assumption, and it’s wrong.”
Especially, it turns out, when it comes to the impact of chronic stress.