Studies Tie Sex Hormones to Women’s Level of Skills

TORONTO —  The strongest scientific evidence to date that the level of sex hormones in the bloodstreams of women can affect their thought processes, reasoning ability and muscular coordination was reported at the annual meeting of the Society for Neuroscience here Wednesday.

Research conducted on three groups of women showed that their success on tests of muscular coordination and verbal facility--traits at which, according to previous research, women are generally better than men--increased by as much as 10% during periods of the month when their blood levels of the female hormone estrogen were high, said psychologists Elizabeth Hampson and Doreen Kimura of the University of Western Ontario at London, Canada.

At the same time, the tested women’s ability to solve problems involving spatial reasoning--a trait at which men are generally better--fell by a similar amount, the psychologists told the meeting of 13,000 researchers. Similar results were obtained with post-menopausal women receiving estrogen therapy.

Similar testing has not been performed on men.

“This is a very significant and important result that sheds new light on the effects of hormones on human behavior,” said neuroendocrinologist Bruce McEwan of Rockefeller University, a leading expert in the field who also is attending the conference.

If confirmed by further research, the results could have implications for the time of month at which girls should take standardized tests, such as the Scholastic Aptitude Test taken by high school seniors, because many of the questions on such tests are of the same type used by the researchers. “We’re talking potentially significant differences in results,” Kimura said.

The results also raise the specter of using sex hormones to raise test scores in the same manner that steroids are used to improve athletic performance. “I don’t think we are prepared to consider all the implications,” Kimura said.

Researchers have frequently shown that males and females have different mental abilities in certain areas. Women, on average, score better than men, on average, in tasks that involve precise muscle control and verbal skill.

Men, on average, do better than women, on average, at spatial and mathematical tasks.

The source of these differences has been a matter of intense, often heated, debate. Some researchers have argued, for instance, that women’s lesser ability to solve mathematical problems results from lessened expectations by parents and teachers or lack of exposure to the necessary training.

A growing body of evidence is indicating, however, that the differences arise from differences in exposure to sex hormones during embryonic development. A variety of research with rodents reported here, for example, showed that exposure to sex hormones in the womb affects the way the brain is organized and produces inherent differences in how male and female rats solve mazes, for example.

Similarly, animal research has shown that exposure to sex hormones can change the skill of adult animals. Neurobiologist Jill Becker of the University of Michigan, for example, has shown that female rats trained to walk a narrow beam make fewer errors in that task during the portion of their menstrual cycle when their estrogen levels are high.

Hampson’s and Kimura’s studies are the first to show such effects in humans, McEwan said.

In one study of 34 women aged 20 to 39, Hampson and Kimura administered various tests when the women’s estrogen levels were high (during the 10 days before menses) and when they were low (near the beginning of the menstrual cycle).

The women did significantly better on tests of verbal and motor skills when their estrogen levels were higher. The average time to say a tongue-twister correctly five times in a row, for instance, declined from 17 seconds to 14. Similarly, the time required for repetitive manual tasks, such as repeatedly pushing a button and pulling a handle, also fell by as much as 10%.

In contrast, the women’s ability to perform tasks involving spatial reasoning declined when estrogen levels were high. Such tasks included discovering hidden figures in complex designs or deciding which of several flat figures could be folded to form a box or other three-dimensional object. Tasks like the last two are frequently found on standardized tests.

Fifty other women in the same age group were tested near the beginning of menses, when estrogen is low, and immediately before ovulation, when estrogen is high, with the same results.

Those results were also obtained with 21 post-menopausal women, all over the age of 50, undergoing estrogen replacement therapy. Such women receive estrogen for 25 days and then go four to six days without receiving the drug, permitting comparisons. These women consistently scored higher on the tests of motor and verbal skill than did 32 post-menopausal women not receiving estrogen therapy.

The experiments were designed so that any mood changes linked to the menstrual cycle did not play a role in the tests, Kimura said.

Similar testing on men is more difficult, she said, because they do not have a comparable monthly hormone cycle. Levels of the male hormone testosterone are higher in the morning than the evening, however, and she is planning studies in which men would be tested.