The Female Brain (15 page)

Another study found that women who have lovers on the side start to fake orgasm more often with their stable partners. Faking orgasm with their steady partners was more common even among women who reported only flirting with other men. Men are biologically geared to look for cues of sexual satisfaction for a reason—such satisfaction is reassurance about women’s fidelity. Faking orgasm may function to distract a woman’s primary partner from her infidelity. For men, faking sexual interest in their main partner is an old ruse to fool the women about the men’s fidelity—sometimes over many years of a marriage. Researchers have shown that when women do engage in extramarital sex, they retain fewer sperm from their main partners (their husbands, in many cases) and experience more copulatory orgasms during their trysts, retaining more semen from their secret lovers. Taken together, these findings suggest that female orgasm is less about bonding with only the nice guys you want to marry than about a shrewd, subconscious, primitive evaluation of outside lovers’ genetic endowment. Women are no more built for monogamy than men are. They are designed to keep their options open, and they fake orgasm to divert a partner’s attention from their infidelities.

F
UEL FOR
L
OVE

The sexual desire trigger for both genders is the androgen testosterone, the chemical that is mistakenly called, by some, the “male hormone.” It’s actually a sex and aggression hormone, and both men and women have lots of it. Men produce it in their testes and adrenal glands, while women make it in their ovaries and adrenal glands. In both males and females, testosterone is the chemical fuel that gets the brain’s sexual engine going. When there’s enough fuel, testosterone revs the hypothalamus, igniting erotic feelings and arousing sexual fantasies and physical sensations in the erogenous zones. The process works the same way in men and women, but there’s a huge sex difference in the amount of testosterone that’s available to “turn on” the brain. Men have on average ten to one hundred times more testosterone than women.

Even flirting is hardwired to testosterone. Studies have found that female rats with high testosterone levels are more playful than others and engage in more “darting” behavior, perhaps the rodent equivalent of sexual sassiness. In humans, the onset of sexual feelings and first intercourse for girls correlate with their testosterone levels. One study of eighth-, ninth-, and tenth-grade girls found that higher levels of testosterone were linked to more frequent sexual thoughts and more masturbation. Another study of adolescent girls revealed that rising testosterone was a significant predictor of first intercourse.

Despite the sharp rise in sexual interest for both teen girls and teen boys spurred by testosterone, there’s still a significant difference in libido and sexual behavior. Between the ages of eight and fourteen, a girl’s estrogen level increases ten to twenty times, but her testosterone level rises only about five times. A boy’s testosterone level increases twenty-five-fold between ages nine and fifteen. With all that extra sexual rocket fuel, teen boys typically have three times more sex drive than girls of the same age—a difference that will persist through life. And while boys have a constantly rising level of testosterone through puberty, girls’ sexual hormones ebb and flow each week—changing their sexual interest almost daily.

If a female’s testosterone drops below a certain level, she’ll lose sexual interest altogether. Jill, a forty-two-year-old premenopausal schoolteacher, had come to me complaining of no libido—which was causing marital problems. Her blood level of testosterone was very low, so I began treating her with testosterone therapy. To track her response to the hormone, I asked her to record how many sexual fantasies or dreams she had and how much she masturbated or was interested in masturbating. If we’d tracked only the number of times she had intercourse, that would most likely have given us a measure of her husband’s libido. I asked her to come back in three weeks to assess her progress. During the time between appointments, Jill mistakenly doubled her dose of testosterone. Her face was blushing bright red when she came into the clinic. She sheepishly told me of her mistake and said her sexual urges were now so strong that she was running into the bathroom between classes to masturbate. She said, “This is becoming a real bother, but now I know what it must feel like to be a nineteen-year-old boy!”

If Jill had waited a little longer, another hormone in her menstrual cycle might have interfered with some of the flood of testosterone in her body. Testosterone is the main trigger the brain needs to ignite sexual desire, but it’s not the only neurochemical that affects female sexual interest and response. Progesterone, which rises in the second half of the menstrual cycle, curbs sexual desire and acts to reverse partially the effect of testosterone in a woman’s system. Some male sex offenders are even given injections of progesterone to decrease their sex drive. Women, too, have a decreased interest in sex when progesterone is high during the last two weeks of their menstrual cycle. Testosterone naturally rises—along with sexual urges—during the second week of the cycle, right before ovulation occurs at the peak of fertility. Estrogen does not cause increased sex drive by itself but peaks along with testosterone at the midpoint of the menstrual cycle. Estrogen tends to make females more receptive to sex and is essential for vaginal lubrication.

T
HE
G
REAT
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EXUAL
D
IVIDE

The sex-related centers in the male brain are actually about two times larger than parallel structures in the female brain. When it comes to the brain, size does make a difference in the way women and men think about, respond to, and experience sex. Men, quite literally, have sex on their minds more than women do. They feel pressure in their gonads and prostates unless they ejaculate frequently. Males have double the brain space and processing power devoted to sex as females. Just as women have an eight-lane superhighway for processing emotion while men have a small country road, men have O’Hare Airport as a hub for processing thoughts about sex whereas women have the airfield nearby that lands small and private planes. That probably explains why 85 percent of twenty-to thirty-year-old males think about sex many times each day and women think about it once a day—or up to three or four times on their most fertile days. This makes for interesting interactions between the sexes. Guys often have to talk women into having sex. It’s not usually the first thing on women’s minds.

These structural changes in the brain start as early as eight weeks after conception, when testosterone in the male fetus fertilizes the sex-related brain center—called the “area for sexual pursuit” in the hypothalamus—to grow larger. A second massive surge of testosterone at puberty then strengthens and enlarges other brain connections in the male that feed information to these sex centers, including the visual, smell, touch, and cognitive systems. The twenty-five-fold increase in testosterone between ages nine and fifteen fuels these larger sex connections in a male’s brain for the rest of his youth.

Many of these structures and connections also exist in the female brain, but they’re half the size. Females, from a biological point of view, simply devote less mental space to sexual pursuits. And their sexual interest ebbs and flows along with their monthly ovarian testosterone cycles. Male brain systems for sex are on alert with every waft of perfume and every female that walks.

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HAT
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OMEN
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ON’T
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NDERSTAND
A
BOUT
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HAT
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EX
M
EANS TO A
M
AN

Jane and Evan, a thirty-something couple, came to see me with a familiar problem. Jane had just started a new job, gained some weight, and begun working extremely hard; she was putting all her time and energy—you might even say all her libido—into making a good impression at work. She found she simply wasn’t in the mood to have sex anymore. Her husband was baffled, since when he had started his new, demanding job the year before, he had wanted sex even more than usual. Nonetheless, once Evan got Jane started, she enjoyed sex and could reach orgasm. She just never felt like getting started. It’s the most common complaint among working women who come into my office.

It seems harmless enough: “Honey, I’m exhausted. I haven’t eaten, work was really tough today, I’d love to cuddle in bed for a while, but really, I just want to eat, watch TV, and go to sleep. Is that okay?” He may say it is, but deep down, ancient wiring takes over. Remember, he’s thinking about sex literally every minute. If she doesn’t want to have sex, it can signal a waning of attraction or perhaps another man. In other words, the fading of love. Evan had insisted they come see me for some couple’s counseling because he was convinced that Jane didn’t love him anymore or, worse yet, that she was having an affair. As we discussed the differences between male and female brains, Jane realized that Evan’s brain’s reality had an unexpected reaction to her not wanting sex. His brain interpreted her lack of physical desire for him as “She doesn’t love me anymore.” Jane started being more sympathetic to what sex meant to her husband.

It’s just like what happens with a woman and verbal communication. If her partner stops talking to her or responding emotionally, she thinks that he disapproves of her, that she’s done something wrong, or that he doesn’t love her anymore. She’ll panic that she’s losing him. She may even think he’s having an affair. Jane truly was just tired and didn’t feel attractive, but the thought took over in Evan’s mind that she was falling out of love with him. He began to appear jealous and possessive as his biological reality made him search for the other man. If she wasn’t having sex with him, she had to be doing it with someone else. After all, he would be. Once Jane understood all this, she told Evan what she had learned about sex being as important to a man as communication was to a woman, and she laughed when he said, “Great. Let’s have more male communication.”

Evan now understood that Jane needed more warm-up time, and Jane now understood Evan’s need to be reassured that he was loved. And so they did have more “male communication.” One thing led to another, and Jane became pregnant. Her reality was about to shift again, and sex—sorry, Evan—would move a little further down the list of things to do. The mommy brain was taking over.

FIVE

The Mommy Brain

M
OTHERHOOD CHANGES YOU
forever,” my mother warned me. She was right. Long after my pregnancy, I’m
still
living and breathing for two—glued to my child, body and soul, by an attachment stronger than I ever thought possible. I’m a different woman since my child was born; and as a doctor, I appreciate why. Motherhood changes you because it literally alters a woman’s
brain—
structurally, functionally, and in many ways, irreversibly.

It’s nature’s way, you could say, of ensuring the survival of the species. How else would you explain why someone like me—with absolutely no prior interest in children—felt born to be a mother after I came out of the drug-induced haze of a difficult labor? Neurologically, it was a fact. Deeply buried in my genetic code were triggers for basic mothering behavior that were primed by the hormones of pregnancy, activated by childbirth, and reinforced by close, physical contact with my child.

As in
Invasion of the Body Snatchers—
or, more accurately,
Invasion of the Brain Snatchers—
a mother is altered from within by the lovable little alien she bears. It’s a trait we have in common with sheep, hamsters, monkeys, and baboons. Take, for example, a female Syrian hamster. Before she bears her young, she’ll ignore or even eat helpless pups. As soon as she gives birth, she gathers up her wriggling newborns, keeps them fed and warm, and grooms and licks them to trigger body functions the pups need to ensure their own survival.

Humans are not quite so biologically determined. A woman’s innate brain wiring, like that of other mammals, responds to basic cues—the growing of a fetus in her womb; her baby’s birth; its suckling, touch, and smell; and frequent skin-to-skin closeness with her child. Even fathers, adoptive parents, and women who have never been pregnant can respond maternally after close, daily contact with an infant. These physical cues from the infant forge new neurochemical pathways in the brain that create and reinforce maternal brain circuits aided by chemical imprinting and huge increases of oxytocin. These changes result in a motivated, highly attentive, and aggressively protective brain that forces the new mother to alter her responses and priorities in life. She is relating to this person in a way she has never related to anyone else in her life. The stakes are life and death.