The implication here is that in an emotionally charged situation, women are better equipped to keep a tighter rein on their tempers, says Gur, who conducted this research. Because they have a bigger braking mechanism than males, he adds, women will try to defuse a volatile situation rather than fly off the handle.
We need look no further than the latest in celebrity bad behavior for an example. When Paris Hilton was arrested on suspicion of drunk driving in the early morning hours last September, the heiress was “cooperative,” according to police sources. But alcohol suppresses the frontal cortex, magnifying an inability to control anger or aggression. Like when Mel Gibson got pulled over . . . well, we all know the rest.
When Larry Cahill and his colleagues at UC Irvine conducted a series of experiments to track sex differences in the brain’s ability to store memories, they came to similar conclusions. Researchers found that the amygdala, which also processes emotional memories, acts differently in men and women. In one study, volunteers were shown a series of graphically violent films while their brain activity was measured using a PET scan.
To process the most disturbing material, men fired up the amygdala’s right hemisphere, which is more in tune with the outside world and communicates with regions that control sight, such as the visual cortex, and motor coordination, like the striatum. Women, on the other hand, activated the left hemisphere, which concentrates more on the body’s inner environment and is connected to the insular cortex, where sensory information is translated into emotional experiences, and to the hypothalamus, the master regulator of such basic functions as metabolism.
Women’s brains may be smaller, but they have other advantages: more gray matter, higher blood flow, and a denser cortex
“When men are presented with an emotionally provocative stimulus, part of the motor system is activated, which may be why men try to resolve the situation by acting on the environment,” says Witelson. “But in women, the hypothalamus is activated, which controls digestion, so it may not be surprising that when a woman is really upset, she feels weak and nauseated and can’t sleep.”
We also know that the brain’s right hemisphere distills the essence of a situation, the central idea, while the left side mulls the finer points and tracks the details. Consequently, this right-left amygdala division may also illuminate why women remember every excruciating detail of a blowup they had on their honeymoon—where they were, what they were wearing, the time of day—while their husbands barely recall the tiff.
In a subsequent UC Irvine experiment, Cahill and his colleagues gave study participants a drug, the beta blocker propranolol, which blunts emotionally charged memories by blocking signals to the amygdala. Then they were shown an emotionally disturbing movie about a boy run over by a car. A week later, when volunteers were quizzed about the film’s content, the males with the beta blocker had trouble remembering the gist of what they saw—the boy being run over by a car. In females, the drug did the converse, interfering with their ability to recall peripheral details, like the fact that the boy had been carrying a soccer ball.
The results were “striking,” says Cahill, “because I assumed sex wouldn’t make a difference. But we have to stop assuming men and women are basically the same because they’re not, which represents a fundamental change in how neuroscience has been doing business—a major zeitgeist change is afoot.”
And as the lines between gender roles continue to blur, our brain architecture may eventually be sculpted to reflect these societal changes, though that structural transformation will take hundreds of generations. “We’re living with brains that evolved in response to conditions over thousands of years, but the brain is a fast learning machine,” says Louann Brizendine of UCSF. “It changes every nanosecond to adjust to what is happening in the environment.“
New behaviors, like learning a new language or how to play the piano, can alter our neural circuitry. Someday soon, Brizendine says, it’s conceivable that the pathways for caring for newborns and doing housework may be activated in men, while women warriors will become hardwired to coolly face danger.
Still, these studies are “in their infancy,” says Melissa Hines, a professor of psychology at the University of Cambridge in England and author of Brain Gender. “We don’t really have a clear overall picture yet.” But the hope is that this research could bring into sharper focus the reasons for the deep gender divide in the incidence of disabling ills that plague millions, says Harvard’s Jill Goldstein, and that understanding could lead to more effective treatments and better methods of prevention.
Vast pieces of the puzzle are missing, in part because imaging techniques are still rather primitive. “To see the brain in action, test subjects need to lie down on a plank inside a scanner or be wired up to a PET machine, which hardly mimics the real world,” says Brizendine. “When we can run around all day long with a miniature MRI scanning apparatus strapped to our head, which could happen in the not too distant future, then we’ll be able to see real sex differences in the brain.”
