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Big test coming up? Having trouble concentrating? Try a little estrogen.
Neuroscientists at the University of California, Berkeley, report in a recent study that hormone fluctuations during a woman’s menstrual cycle may affect the brain as much as do substances such as caffeine, methamphetamines or the popular attention drug Ritalin.
Scientists have known for decades that working memory (short-term information processing) is dependent on the chemical dopamine. In fact, drugs like Ritalin mimic dopamine to help people concentrate. Researchers have also had evidence that in rats, estrogen seems to trigger a release of dopamine. The new study from Berkeley, however, is the first to show that cognition is tied to estrogen levels in people—explaining why some women have better or worse cognitive abilities at varying points in their menstrual cycles.
The Berkeley team examined 24 healthy women, some of whom had naturally high levels of dopamine and some of whom had low levels, as indicated by genetic testing. As expected, those with the lower levels struggled with complicated working memory tasks, such as repeating a series of five numbers in reverse order. When the test was repeated during ovulation, however, when estrogen levels are highest (usually 10 to 12 days after menstruation), these women fared markedly better, improving their performance by about 10 percent. Surprisingly, those with naturally high dopamine levels took a nosedive in their ability to do complicated mental tasks at that point in their cycle.
According to Ph.D. student Emily Jacobs, who conducted the study, dopamine in the brain is a “classic Goldilocks scenario.” For women with the lowest levels—about 25 percent of the general population—increased dopamine during ovulation will sharpen cognitive functions, whereas for the 25 percent of women with the highest levels, ovulation seems to take them beyond a threshold and to impair thinking. The remaining half of women fall somewhere in between and were not a part of the study.
The work has broad implications. Jacobs says it may mean that caffeine, which triggers a dopamine release, and Ritalin-like drugs are less effective—or even detrimental—at certain times of the month for some women, when estrogen is spiking. More broadly, she hopes to remind scientists studying brain disease that women’s and men’s brains, though equal in aptitude, are not the same.
“There are pretty important differences,” Jacobs says. “And until we figure out how they differ in a normal state, we can’t predict how they differ in a diseased state.” [For more on sex hormones in the brain, see “Different Shades of Blue“.]