This Is Your Brain on Sex (22 page)

Due to the stability of oxytocin levels both during pregnancy and after, a woman’s level even early on in her pregnancy can predict her later maternal interactions with her baby. Think about it: this means that even in the first trimester, long before a woman could ever nurse or even gaze at her child, oxytocin is mediating something in the brain that will lead to a certain quality of care. What might that be? No one is quite sure, though it’s likely to involve a variety of different processes and neurochemicals, including estrogen, progesterone, and oxytocin.
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Neuroimaging and Maternal Love

Several researchers have also undertaken neuroimaging studies of maternal love. Semir Zeki, following on the heels of his romantic love study, compared romantic love to that of a mother for her child. He hypothesized that similar brain circuits would be activated. Once again he relied on visual input. Twenty mothers passively viewed photos of their own infant child (with an age range of nine months to three and a half years), another familiar child of about the same age, the woman’s partner, a person she disliked, an unknown child, and an unknown adult. They were instructed to look at the photos and relax while blood flow was measured in the fMRI scanner.
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Zeki and his colleagues found that when the women were gazing at photos of their own children there was a significant increase in blood flow in the substantia nigra, the dorsal and ventral striatum, the thalamus, and parts of the prefrontal cortex. Notably, these areas are rich in both oxytocin and vasopressin receptors, as well as dopaminergic neurons—and, as you’ve noticed, they show some overlap with areas activated in romantic love. The results led Zeki to conclude that love, whether romantic or maternal, is a push-and-pull mechanism. That is, the specific brain activation underlies a softening of our judgment and assessment skills. We view our loved ones, children and romantic partners alike, with rose-colored glasses. When Nicolas Read originally made that crack about
“sexy” babies, he was referring to this. Let’s face it, one’s own baby is pretty damn irresistible. A screaming, pooping, and exhaustion-inducing little machine, perhaps—yet irresistible nonetheless.

I am not exaggerating when I say there is no kid more awesome than mine. My brain tells me it is so. And when my friend Alyson says her kid is the best, she’s not wrong either. Even when faced with evidence directly to the contrary, we feel—we
know
—that our kids are fantastic. If we did not have this built-in push-and-pull mechanism, if we did not inherently recognize the “sexiness” of our own offspring, we might choose to not feed them or to leave them on the side of the road when they ask us “Are we there yet?” for the thousandth time on the way to Grandma’s house. Couple this neurobiological push on our judgment systems with the pull of dopamine surges in the reward circuitry, and we can create a strong, lasting bond with our children.

Some of the areas activated in Zeki’s maternal love neuroimaging study.
Illustration by Dorling Kindersley.

Ellen Leibenluft, a scientist at the National Institute of Mental Health, did a similar study with mothers of older children. However, Leibenluft had moms do a simple cognitive task while looking at photos in the fMRI scanner; participants had to indicate
whether the photo they were viewing was the same as the one they had viewed earlier. She found a pattern of activation similar to that in the Zeki study, but she also found maternal activation in the anterior paracingulate, posterior cingulate, and superior temporal sulcus. Whether this difference has to do with the children’s being older or the fact that the participants were asked to do a cognitive task instead of just looking at photos is unknown. However, it is possible that there are different brain systems involved in dealing with an infant compared to parenting older children.
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A Baby’s Cry

Photos are all well and good, but babies have other ways of capturing a mother’s attention, namely, crying. Might that same sound that could set my breasts a-leaking from across the room also cause a unique pattern of brain activation when heard in the fMRI? James Swain, of Yale University, used fMRI to measure blood flow in nine first-time mothers a few weeks after birth while they listened to a recording of their own baby’s cry and another baby’s. When moms tuned in to their own babe’s cries, Swain and his colleagues found activation in many of the love-related areas, including the basal ganglia, cingulate, amygdala, and insula. When these moms were rescanned three to four months later, the amygdala and insula were no longer activated. Swain hypothesizes that this change in cerebral blood flow may suggest more familiarity. It makes sense; when you are a new parent, a baby’s cry can be quite alarming. I spent my first month at home with my son in a bit of a tizzy, looking at every baby-related book and website in hopes of finding some secret instruction manual that would help me decode exactly what he wanted. Over time, as I became more acquainted with his cries, his idiosyncrasies, and his natural schedule, I became less anxious. That, Swain contends, may account for the changes in activation pattern.
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Madoka Noriuchi, a researcher at Tokyo Metropolitan University, also looked at maternal neural activation in response to a baby’s cry—but her study had a twist. Noriuchi and her colleagues measured cerebral blood flow as moms watched video stimuli, without sound, of an infant crying for his mother as well as a clip in which the infant smiled at her. These clips, the researchers argued,
demonstrated two key infant behaviors that help promote and strengthen the mother-infant bond. The group compared how the mother’s brain reacted to her own child versus another as well as between the smiling and crying clips. They found that just watching one’s own baby activated the orbitofrontal cortex, the anterior insula, and parts of the putamen. When her own baby was in distress and cried for her, there was additional activation in the caudate nucleus, anterior cingulate, posterior cingulate, thalamus, substantia nigra, and posterior superior temporal sulcus. The response to the crying resulted not only in a different pattern of activation but also in stronger activation. This, the authors argued, suggests the brain is hard at work, taking cues from babies so moms can learn, adapt, and consequently meet the many demands involved in caring for an infant.
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Some of the areas of activation found across different maternal love studies.
Illustration by Dorling Kindersley.

There has been a significant amount of overlap in the maternal neuroimaging studies, studies looking at romantic love, and studies involving oxytocin and dopamine. With any neuroimaging study in this field, says Stephanie Ortigue, who included these mother love studies in her neuroimaging meta-analysis of love, the qu
estion is “So what?” Though we know that many brain areas are activated in a variety of different love-related paradigms, and there has been some replication in findings, it is still hard to pinpoint what exactly these different brain regions are doing and how they are working together to forge the mother-child bond. It is even difficult to know with certainty if maternal attachment is significantly different from any other kind of attachment.

These uncertainties have led some researchers to take a step back. Perhaps before we can make any sense of brain activations involved in maternal love, we need to better understand the kinds of changes motherhood makes to the brain overall. Consider all the bodily alterations that come with pregnancy. The bulging belly and thick, voluminous hair are the obvious ones. Pregnant moms may also scare you with tales of growing a bigger nose and feet. Any mother will tell you it’s a whole-body kind of experience. Why wouldn’t we see some changes to the brain too?

“The animal literature suggests there are actual structural changes in the brain, especially during the early postpartum period. These are changes where the brain grows bigger,” said Pilyoung Kim, a postdoctoral fellow formerly of Yale University. “To be clear, these are local changes—some brain areas experience growth and others remain the same. But the hypothesis is any changes that occur at this time probably play an important role in the development of parenting behavior.”

Chief among those behaviors is attachment, or love. But there’s more to being a good parent than that. You have to provide, problem-solve, and learn—whether that involves differentiating cries, avoiding dangers, or changing a horrendously poopy diaper without getting any on the only white shirt that still fits you. There is this pervasive notion that new moms are not so smart. The condition is often referred to as “mommy brain,” and given the lack of sleep and changing priorities, I can see why the idea is so prevalent. The animal literature, however, does not support the idea that motherhood makes you stupider. Mother rodents navigate mazes faster, capture more prey than virgins do, and do better on a variety of memory and cognitive tasks.

No one, of course, is judging your average rat for accidentally leaving the groceries in the back of the car overnight or losing her keys for the third time this week. So what might truly constitute a “mommy brain”? Kim and her colleagues decided
to find out by examining changes in the brains of nineteen moms at a few weeks after giving birth and then three months later. The group found an increase in volume in the prefrontal cortex, the parietal lobes, and many midbrain areas, and when moms had very positive thoughts about their babies, there was an increase in the hypothalamus, amygdala, and substantia nigra. It’s a fascinating discovery: positive perception of motherhood mattered in some of those volume changes. That, Kim argues, bolsters the argument that interactions with one’s baby, an environmental variable, are just as important as any biological changes that occur alongside pregnancy and childbirth.
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“Hormonal changes play an important role during the pregnancy, especially toward the end just before and after childbirth,” she said. “There’s evidence that oxytocin and estrogen levels all go up prior to a child’s birth, and that helps the mother’s brain change so [she] will perceive the infant as positive and rewarding rather than aversive. But after birth, playing and interacting with the baby also helps with further restructuring.”

Pilyoung Kim and her colleagues found an increase in volume in the prefrontal cortex, the parietal lobes, and many midbrain areas in mothers a few weeks after giving birth. When moms had positive thoughts about their babies, there was also an increase observed in the hypothalamus, amygdala, and substantia nigra.
Illustration by Dorling Kindersley.

Kim maintains that both nature and nurture are
involved in specific changes to the brain. The brain volume changes suggest an increased capacity for integrating sensory stimuli, improved higher-level cognition, and better ability to enjoy all the dopamine-related rewards of love. But might these changes be necessary only to adapt and care for a newborn infant? When I asked Kim how long these changes last, she paused. “We don’t know. It’s possible that as long as parenting is a major part of your life, the brain structure remains,” she said. “But I can also imagine that once parenting is not a major activity in your life, the brain may go through changes again.”