Woman: An Intimate Geography (55 page)

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Authors: Natalie Angier

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BOOK: Woman: An Intimate Geography
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In the extraordinary mechanics of human birth, then, we see still another reason that humans must have others around them, and that humans are the most social of primates. We also see another thread of evidence that the gynocracy, the unified front that females can assume in times of need, is not alien to the human race but is rooted in our distant past and in the loneliness of standing on our own two feet.
The chemistry of stress bears the seeds of its own relief. When you get past lust and obsession, or when the expulsive frenzy of birth is through, you may reach a state of attachment, a neurochemical antidote to the spattering profligacy of aggression and desire. Anxiety is catabolic and energy intensive. Attachment is anabolic and energy conservative. We are born to aggress. We are born to coalesce. We know something about the former. We know much, much less about the latter, its counterweight. We suspect (and
suspect
is the word we must use) that the state of attachment has something to do with the peptide hormone oxytocin and its close molecular cousin, vasopressin.
Oxytocin has been called the love hormone. It's a dopy, wishful phrase, so patently reductionist that, like the terms
the gay gene
and
the intelligence gene
, it hardly deserves being gainsaid. Still, oxytocin may be a player in the sensation of love. Our feelings must be felt somehow, through a physical medium, and oxytocin has the lipstick traces of an emotional emulsifier. Oxytocin shows up in circumstances where affiliative behaviors are called for. During childbirth, it is released from the brain into the bloodstream. It has a practical and mechanical job to do. It triggers uterine contractions. Pitocin, the drug given to pregnant women to jumpstart recalcitrant labor, is a synthetic version of oxytocin. Oxytocin also stimulates the letdown reflex, the pulsing of milk from the breast cells through the ducts and out the nipple. Oxytocin stimulates maternal muscle contractions above and below the belt. It gets the baby born. It gets the baby fed. It might as well help get the baby loved, for without love the mother may look at the small and squawling creature before her and ask, Well, how did I get here? And how can I escape?
Vasopressin also is a good candidate for a bonding hormone. It is molecularly similar to oxytocin, and it has a practical function that, like oxytocin, is essential to lactation. It helps the body retain water, and

 

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if you can't retain fluids, you can't make milk. Vasopressin enhances memory, and it's a good idea to remember those who are significant to you your children, for example, or a lover worth loving. Oxytocin and vasopressin are quite swift in their actions, which is what you want of hormones expected to help referee behavioral revolutions in a brief period of time. One minute you're a pregnant dam, still antsy, still free; the next you're a nursing mother, expected to sit and to give and to love and to sit.
''Nature is conservative" says Carol Sue Carter, of the University of Maryland, the grande dame of oxytocin research. "She rarely comes up with something she uses only once. The functions of oxytocin evolved from something primitive and basic to something far more elaborate."
Oxytocin and vasopressin sound good, sound lovely, but the data on their ramifications for human affairs remain slender, because you can't do good experiments with the hormones. Oxytocin is a peptide hormone, as opposed to a greasy steroid hormone like estrogen or testosterone. The greasiness of a steroid allows it to slip back and forth from brain to peripheral bloodstream and back to brain. For a peptide hormone, traffic is unidirectional, from brain to blood. The hypothalamus generates oxytocin for the body as needed, and keeps some for itself, for local behavioral or cerebral purposes; but whatever oxytocin is released into the bloodstream cannot penetrate the blood-brain barrier and go home again. When a pregnant woman is given an intravenous drip of Pitocin, it doesn't reach her brain. It reaches her uterus, and makes her think her midriff is being winched by Josef Mengele himself, but that's it. Thus, you can't do an experiment where you give a person an oxytocin tablet and ask, Are you feeling maternal yet? How about affiliated, cuddly, or at one with your oppressors? The exogenous oxytocin won't get to where it needs to go to sway behavior, if it is to sway.
Most of what we know about oxytocin and vasopressin we know from experiments on animals such as prairie voles, hamsters, and rats, whose brains are considered fair game for hands-on manipulations. When oxytocin is delivered directly into the central nervous system of a rat, the rat will start sidling up to another rat, seeking physical contact, a soft place to lay its snout. Female prairie voles form pair bonds after they have sex, and they also release oxytocin upon having sex. A female vole, given a shot to the brain of either oxytocin or vasopressin and then

 

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presented with a male, will act as though she has copulated with him and want to be around him and never leave his side. The same for a male vole: deliver a bolus of oxytocin or vasopressin to his central nervous system, and he will bond faithfully with the next female he meets. Conversely, a female vole treated with an oxytocin antagonist, which blocks the activity of the peptide, will have trouble settling down with a partner or caring for one wheat-furred fellow over another.
Oxytocin can make virgin females motherly. When female voles are given oxytocin through their cerebrospinal fluid, within thirty minutes they're snuffling pups presented to them, picking them up and retrieving them if they stray. A ewe usually is a good mother, but she will turn bad if for some reason she is separated from her lamb shortly after birth. Then she is likely to reject the lamb, refusing to nurse it. Sheep farmers have a way of persuading her otherwise. They stimulate her vagina with a kind of sheep dildo. The tickling releases a stream of oxytocin in her brain, and she then takes the lamb to udder. An oxytocin pump in her spinal cord will have the same maternogenic impact.
Vasopressin is somewhat statelier than oxytocin. It can instigate maternal behaviors in female rodents, but it takes an hour or so longer than oxytocin. By the reigning theory, vasopressin is of comparatively greater importance to the induction of loving and parental behavior in males than in females. Among prairie voles, who form the close-knit monogamous pair bonds so heartwarming to humans, vasopressin levels soar in males after mating, but not in females; it is after mating that a male will cleave to his partner. Among laboratory rats, males show varying degrees of paternal involvement, depending on the strain. The least fatherly of rat varietals is the Brattleboro rat. He is a dirty rat. He is also notably deficient in vasopressin.
What is sweet for a rodent is suggestive for a simian. In one of the few oxytocin experiments performed on primates, virgin female rhesus monkeys received injections of the hormone to the central nervous system. A few minutes later, an infant monkey was placed in their enclosure. The females walked over to it. They ogled it. They poked it gently and smacked their lips at it in a kind of kissing gesture. The monkeys also became friendlier toward their human observers, refraining from yawning and grimacing and otherwise displaying typical signs of rhesus resentment. By contrast, virgin females given control shots of

 

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saline showed no maternal leanings, did not smack their lips at a presented infant, and yawned peevishly at their captors.
Scanty though they are, the data from human studies conform to the model of oxytocin and vasopressin as emotional ligaments. Kerstin Uvnas-Möberg, of the Karolinska Institute in Sweden, has done much of the human work. She studies nursing mothers, in whom oxytocin levels are particularly high. Think of a breastfeeding woman, she says. Think of her singular physiology. Oxytocin is stimulating her milk letdown that much is familiar. But milk ejection is only part of the story. Oxytocin, in concert with other peptides, also expands blood flow to the breast. The engorgement turns the breast warm, warmer than it's ever been. Heat radiates from the nursing woman as though she were feverish, as though she were a flagstone in the sun. She feeds the baby fluids and bathes the baby in warmth.
"There's a whole transfer of warmth, and that's very important, isn't it?" Uvnas-Möberg says. "Isn't that the substrate for love? To transmit warmth? When we talk about a loving person, we call her a warm person. A person who refuses to love is called a cold person. In this case, psychology has borrowed from very deep aspects of physiology." Uvnas-Möberg speaks in a warm voice, a hushed and intimate voice, as though we were sitting in a room and breastfeeding together rather than sitting in an office at the Karolinska. Institute fully buttoned up, no infants in sight. She wears a suit the color of grasshopper pie, and her cheeks are round, and her face is rosy and shiny, like polished fruit.
"To mother a child is a matter of giving out energy and warmth, which both require calories" she says. "Which is a very dangerous thing, an expensive thing. Which means that oxytocin has another side, a saving side. Because if there is going to be an equation that comes out right, you have to take in somewhere what you're losing in warmth and milk."
Oxytocin is a giving hormone, and it is a conservative hormone, she says. It acts on the gut to slow digestion and allow every possible ingested calorie to be captured by the body. It increases insulin concentrations, so that as much sugar in the blood as possible is pulled into cells rather than peed away. A nursing mother should save energy in her behavior too. She should feel calm, be able to sit and sit. Fidgeting wastes calories. Feeling anxious wastes calories. Feeling calm conserves

 

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them, helps balance the equation, giving warmth, radiating warmth, but gaining anabolic strength, for the more you give, the more oxytocin is produced, and the greater the gut's conservation capacities are, and the more serene you feel. It's like one of those white sales in a department store: the more you spend, the more you save.
Uvnas-Möberg and her colleagues have studied women as they nurse and hold their infants. They watch the behavior of the mothers and have the mothers take personality tests. They ask the mothers how long they generally breastfeed during each session. The scientists measure oxytocin and other hormone levels in the blood, taking samples every thirty seconds for ten minutes of breastfeeding. They have found that oxytocin secretion patterns differ among women. In some there are peaks and valleys: the oxytocin is secreted in bursts. In other women, the pattern of secretion is fairly flat, basin and range rather than mountains. "It turns out that the more peaks you have, the higher your total oxytocin concentration, and the longer a woman tends to breastfeed," she says. "It's also correlational to personality changes. Women with the most peaks report feeling the greatest calm. They say they feel more emotionally accessible than they did before. They say they feel attached to their children. Which is very reasonable. The higher the oxytocin, the longer they breastfeed. The longer they breastfeed, the more time they spend in contact with the baby, and the closer they feel, physically, emotionally, and, I might add, neurochemically."
A mother does more than nurse and warm the baby. As she holds the baby, she touches it. She strokes the infant to soothe it. "You know the right way to stroke somebody," Uvnas-Möberg says. "You know what works and what doesn't. If you do it like this, too fast, that's irritating." She rubs her hand up and down rapidly on her arm to demonstrate. "If you do it too slowly, that doesn't work either." She gives her arm a dull, slow stroke. "But now, if you do this, if you stroke steadily and calmly, you know, this is right, this is good and true." She strokes her arm rhythmically, and I watch, and as I watch I feel vicariously stroked and vicariously soothed. "This rate is about forty strokes per minute,'' Uvnas-Möberg says. "This is the same rate at which we stroke our pets." Oxytocin again enters the picture. When the scientists take blood samples of women as they stroke their infants, they see the same activation

 

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of oxytocin systems seen with breastfeeding. The mother secretes oxytocin as she caresses her child, for her hand is feeling the soothing sensation of stroking, just as her child feels the balm of being stroked. The mother describes a sense of calm, and if you pinch her, she will hardly feel it. "We know that you can induce pain reflexes from anywhere with a pinch," says Uvnas-Möberg. "But we can induce sedation and pain relief by touching and stroking any part too. Somehow we know that, don't we? It's an innate knowledge, though we forget it sometimes, or feel embarrassed that we know it."
Touch conveys warmth. To stroke is to underscore that we are touching, and giving, and there. Perhaps we were depilated for the sake of touch and the ease with which it coaxes love. We stroke our babies, and we rock them back and forth. Shopping for a nursing rocker is one of the pleasures of impending motherhood, and just the thought of rocking the baby back and forth fills you with warmth and joy. Women in China take a warm shower during labor, and they almost never need Pitocin, for the warm, pulsing water liberates their natural stores of oxytocin; and women in the West are learning as much, for some natural birthing centers now offer Jacuzzis. Other mammals lick themselves during labor, lick lick lick. And afterward they lick their pups or kittens, and the babies nuzzle into it; this is as lovely as life will be. A steady caress inveigles oxytocin secretion. The gentle rhythmic stroking is like the pulsing of a milk duct, like the rate at which the infant reflexively, rhythmically suckles at the breast. This is the rhythm of love: forty beats a minute.
The rhythm of love. Orgasm is another rhythmic sensation, and it too clocks in at about forty to fifty throbs a minute, and the uterus contracts during orgasm as it does in giving birth. Oxytocin's frequency; oxytocin's handiwork. In one study women were asked to masturbate to climax, and their blood levels of oxytocin were measured before and after orgasm. The concentration of oxytocin climbed slightly but measurably with climax, and the greater the increase, the more pleasurable the women reported their climax to be. Some nursing women say they feel not so much sedated while they breastfeed as exhilarated, almost orgasmic, their uterus pulsing along with their milk ducts, along with the baby's suckling mouth. Exhilaration is not really different from

 

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