The Female Brain (16 page)

In modern society, where women are responsible for not only giving birth to children but working outside the home to support them economically, these changes in the brain create the most profound conflict of a mother’s life. Nicole, a thirty-four-year-old investment banker, devoted years of her life to working hard in high school in order to get into Harvard University so that she could enter a prestigious career track giving her financial security and independence. Getting her Mrs. along with her B.A. was the furthest thing from her mind. After college she traveled the world, settled for a while into a job in San Francisco’s financial district, then entered business school at the University of California, Berkeley. She spent four years there, getting a double master’s in business administration and international relations in order to prepare herself for a career in the global economy. She finished Berkeley at twenty-eight and moved to New York, where she got a job as an associate at an investment bank.

The more you do something, the more cells the brain assigns to that task, and Nicole’s circuits were becoming entirely focused on her job and career path. The next two years involved grueling but rewarding eighty-hour workweeks. She wanted to make her mark, and she put her mind, body, and soul into bonding with her career. But soon she met and fell in love with Charlie, a cute southern lawyer who worked across the hall from her; her brain began dividing the assignment of cells between her attachment to Charlie and her career. Thus, Nicole spent her early thirties learning to balance her relationship, which eventually turned into marriage, with her demanding job. There would soon be a third little person coming into her life, and the brain cells would be forced to divide again.

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Biology can hijack circuits in spite of our best intentions, and many women experience the first “mommy brain” symptoms long before they actually conceive a child, especially if they’ve been trying for a while. “Baby lust”—the deep-felt hunger to have a child—can hit a woman soon after she’s cradled someone else’s warm, soft newborn. Suddenly, even the least child-focused females can start craving the tender, delicious feel and smell of babies. They may chalk it up to ticking biological clocks, or the “me-too” influence of peers, but the real reason is that a brain change has occurred and a new reality has set in. The sweet smell of an infant’s head carries pheromones that stimulate the female brain to produce the potent love potion oxytocin—creating a chemical reaction that induces baby lust. After visiting my sister’s new baby, Jessica, for the first time when she was three months old, I was totally obsessed with babies for a long time. In a sense, I’d come down with an infectious condition that I’d caught—literally and physically—from my new niece: nature’s sneak attack to trigger the desire to have a baby.

The mommy-brain transformation gets under way at conception and can take over even the most career-oriented woman’s circuits, changing the way she thinks, feels, and what she finds important. Throughout pregnancy, a woman’s brain is marinated in neurohormones manufactured by her fetus and placenta. Nicole was soon to experience firsthand the effects of these hormones. She and Charlie had barely come back from a weekend of love in upstate New York when it started to happen. If we had an MRI scanner looking inside Nicole’s brain, we’d see just her normal female brain as the sperm penetrates the egg. Within two weeks after the egg has been fertilized, it implants firmly in the uterine lining and attaches to Nicole’s blood supply. Once her blood supply and that of the fetus have been joined, hormonal changes begin in Nicole’s body and brain.

Progesterone levels start to climb in Nicole’s bloodstream and brain. She soon feels her breasts become tender and her brain getting sedated. We’d see her brain circuits become mellow as she got a sleepy feeling, which would make her need to rest and eat more than usual. Her brain’s thirst and hunger centers are switched on full blast by the rising hormones. She will now need to produce up to double her normal blood volume. She never wants to be far from her water bottle, a faucet, or the bathroom. At the same time, her brain signals for eating, especially in the morning, become finicky as her brain is changing how it reacts to certain smells, especially of foods. She wouldn’t want accidentally to eat something that would harm her fragile fetus during the first three months of pregnancy. This is why her brain is now overly sensitive to smell, which may make her nauseated most of the time. She may even get to the point of retching every morning—or at least feeling she would like to—all because her brain circuits for smell have changed massively thanks to the hormones of pregnancy.

Nicole struggles to get through every day during these first months of pregnancy. At work, all she can do is sit and stare at her stapler and try not to throw up. By the fourth month, however, a big transition occurs. Her brain has become accustomed to the massive hormone changes, and she can eat normally, even ravenously. Both her conscious and unconscious brain is now focused on what is going on in her uterus. As the fifth month rolls around, she starts to feel little gas bubbles in her abdomen; perhaps at first she thinks they are the usual gas gurgles from a big meal. But no, her brain is registering these as movements by her baby. The mommy brain has been hormonally primed for months, but not until now is Nicole consciously aware that she is growing a baby. She has been pregnant for almost half a year, and her brain has been changing and enlarging its smell circuits, thirst circuits, and hunger circuits, and putting the brakes on the pulsing cells in the hypothalamus that usually trigger her menstrual cycle. She is now ready for the love circuits to grow.

With each new kick or movement, she starts getting to know her baby and longingly fantasizes about what it will be like to hold him or her in her arms. She can’t quite imagine it but hungers for it nonetheless. This is also the first time Charlie may become interested in his growing child—feeling the kicks and listening to Nicole’s abdomen for the little heartbeats. The baby may even tap-tap-tap back at him, and yes, fathers usually fantasize about a boy and mothers about a girl.

I remember those intense cravings for odd foods and feeling like I would surely vomit at even the whiff of greasy food. All these changes are brain signals that something or someone has invaded your system. Progesterone spikes from ten to a hundred times its normal level during the first two to four months of pregnancy, and the brain becomes marinated in this hormone, whose sedating effects are similar to those of the drug Valium.

This tranquilizing effect of progesterone and also high estrogen help protect against stress hormones during pregnancy. Those “fight-or-flight” chemicals, such as cortisol, are produced in large quantities by the fetus and placenta, so the mother’s body and brain are flooded with them. By late pregnancy, the stress hormone levels in a woman’s brain are as high as they would be during strenuous exercise. Oddly enough, though, these hormones don’t result in the feeling of stress during pregnancy. Their impact is to make a pregnant woman vigilant about her safety, nutrition, and surroundings, and less attuned to other kinds of tasks, such as making conference calls and organizing her schedule. That’s why, especially in the last month or so of pregnancy, Nicole starts to feel distracted, forgetful, and preoccupied. Not since puberty have there been so many changes going on in her brain at once. Of course, each woman’s response depends on her psychological state and the events in her life, but these are the biological underpinnings of her changing reality during pregnancy.

At the same time, the size and structure of a woman’s brain are changing, too. Between six months and the end of pregnancy, f MRI brain scans have shown that a pregnant woman’s brain is actually shrinking. This may be because some parts of her brain get larger as others get smaller—a state that gradually returns to normal by six months after giving birth. In animal studies, we’ve seen that the thinking part of the brain, the cortex, enlarges during pregnancy, revealing the complexity and flexibility of female brains. Scientists still don’t know exactly why brain size changes, but it seems to be an indication of the massive brain restructuring and metabolic changes going on. It’s not that a woman is losing brain cells. Some scientists believe the mother’s brain shrinks because of changes in cellular metabolism required for restructuring brain circuits—getting ready to turn some one-lane highways into superhighways. So while the body is gaining weight, the brain is actually losing it. In the final one to two weeks before giving birth, the brain begins to increase again in size as it constructs large networks of maternal circuits. Otherwise, the child’s first sentence would have to be “Mommy, I shrunk your brain.”

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IRTH OF THE
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As her due date approaches, Nicole’s brain will become almost exclusively preoccupied with her baby, and with fantasies about how she is going to make it through all the pain and physical effort to push out a healthy child without killing herself or the baby. Her mommy brain circuits switch to high alert. She gets bursts of energy even though she feels like a beached whale and can only waddle. Charlie also becomes preoccupied, not with the birthing process so much as with physical things—such as space for the baby, painting its room, and acquiring all the necessary equipment, most of which Charlie had purchased months ago. He suddenly thinks of six more things they will need. The daddy brain circuits are rapidly connecting up for the big event. Now the countdown to birth begins.

Nicole was given a due date but told it could be up to two weeks earlier or two weeks later. This is because each baby gets ready to be born at its own pace. This will be the first of many times Nicole and Charlie are held hostage to the innate timing of their child’s developmental schedule, which rarely fits with what they have in mind.

The day finally arrives. Nicole’s water breaks, and the amniotic fluid comes flooding down her legs. The baby is head down and ready. The mommy brain is switched on right at birth by a cascade of oxytocin. Cued by signals coming from the fully developed fetus when it is ready to be born, a pregnant woman’s level of progesterone suddenly collapses, and oxytocin pulses flood her brain and body, causing the uterus to start contracting.

As the baby’s head moves through the birth canal, more bursts of oxytocin fire in the brain, activating new receptors and forging thousands of new connections between neurons. The result at birth can be euphoria, induced by oxytocin and dopamine, as well as profoundly heightened senses of hearing, touch, sight, and smell. One minute you’re sitting there, an awkward, beached whale, and the next your uterus is lurching into your throat and you can’t believe that it’s feasible to do the pelvic equivalent of expelling a watermelon through your nostril. After too many hours for most of us—the ordeal is over and your life and brain have changed forever.

In the mammal world, there’s nothing unusual about these brain changes at birth. Take sheep, for instance. When a baby lamb passes through its mother’s birth canal, oxytocin pulses rewire the ewe’s brain in minutes, making it exquisitely sensitive to its baby’s smell. For five minutes or less, just after birth, she’s able to imprint the odor of her newborn. After that, she’ll permit only her own lamb to nurse, rejecting others, which have unfamiliar smells. If she doesn’t get to smell her own baby in those first five minutes, she will not recognize it and thus reject it, too. The act of birth triggers rapid neurological changes in the ewe that can be seen in her brain anatomy, neurochemistry, and behavior.

For the human mother, the lovely smells of her newborn’s head, skin, poop, spit up breast milk, and other bodily fluids that have washed over her during the first few days will become chemically imprinted on her brain—and she will be able to pick out her own baby’s smell above all others with about 90 percent accuracy. This goes for her baby’s cry and body movements, too. The touch of her baby’s skin, the look of its little fingers and toes, its short cries and gasps—all are now tattooed on her brain. Within hours to days, overwhelming protectiveness may seize her. Maternal aggression sets in. Her strength and resolve to care for and protect this little being completely grab the brain circuits. She feels as if she could stop a moving truck with her own body to protect her baby. Her brain has been changed, and along with it her reality. It is perhaps the biggest reality change of a woman’s life.

Ellie, a thirty-nine-year-old first-time mother, had been happily married for two years to a self-employed salesman when she came to see me. During the first year of their marriage, she had lost a baby to miscarriage. Within six months she was pregnant again. Soon after her daughter’s birth, she began having “freak-outs,” as she called them, about her husband’s earning power and lack of health care benefits. In truth, their financial situation hadn’t changed at all, and she’d never had any of these misgivings before. Now, however, she was blazingly angry with her husband for not providing a more secure home for her and their baby girl. Her needs and reality had changed radically, virtually overnight, and her new, protective maternal brain was tightly focused on her husband’s ability to provide for the family.

With their aggressive, protective instinct fully primed, mothers become hypervigilant about all aspects of their home turf, especially infant safety, such as having babyproof electrical plug covers, installing latches on the kitchen cabinet doors, and making sure everyone washes their hands thoroughly before touching the baby. Like a human global positioning system, a mother’s brain centers for sight, sound, and movement are honed in on monitoring and tracking her baby. This increased vigilance can take all forms, depending on the threat a mother sees to the safety and stability of her “nest.” Even reassessment of her husband’s role as provider is not unusual.