by D. F. Swaab
1
Development, Birth, and Parental Care
THE SUBTLE INTERACTION BETWEEN MOTHER AND CHILD AT BIRTH
Birth is too important to be left entirely to your mother.
I congratulate my mother on this anniversary of her suffering and thank her for bringing me into the world.
Text message on the occasion of her birthday
from a Chinese daughter to her mother
Somebody once suggested that I went in for brain research because my father was a gynecologist, the theory being that I chose the organ that lay as far as possible from his field of work. This psychoanalytical explanation fails to take account of the research I’ve done in the function of the brains of both mother and child during childbirth, working with gynecologists like Kees Boer at Amsterdam’s Academic Medical Center. The conclusion of Boer’s PhD thesis was that smooth childbirth requires good interaction between the brains of mother and child.
Both brains play a role in speeding up labor by secreting a hormone, oxytocin, into the bloodstream that makes the uterus contract. The mother’s biological clock imposes a day-night rhythm on the birth process, which explains why most children are born during the quiet phase, at night and in the early hours of the morning. That’s also the time when birth progresses fastest and requires the least assistance.
Labor starts when the baby’s blood sugar level starts to drop—a sign that the mother can no longer provide the growing child with sufficient nourishment. Michel Hofman has calculated that labor is triggered at a stage when the child accounts for around 15 percent of the mother’s metabolism. That point is reached earlier by twins, triplets, and so on, which is why they are born prematurely. While still in the womb, the brain cells in the child’s hypothalamus respond to a drop in blood sugar level in the same way that they later respond to a lack of food in adulthood, by stimulating the stress axis. This induces a series of hormonal changes, making the uterus contract (fig. 3). The contractions, stimulated by oxytocin, make the baby’s head press against the cervix. This in turn triggers a reflex, via the mother’s spinal cord, which causes the release of yet more oxytocin. The baby’s head then exerts more pressure, triggering the same reflex. The child can only escape from this chain reaction by being born.
Various psychiatric disorders are associated with a difficult birth. It has long been known that a high percentage of patients with schizophrenia experienced problems at birth, such as delivery by forceps or vacuum pump, low birth weight, premature birth, premature breaking of the waters, or time spent in an incubator. It was once thought that difficult births caused brain damage, leading to schizophrenia. We now know that schizophrenia is an early developmental brain disorder largely caused by genetic factors (see chapter 10). So a difficult birth can be seen as a failure of interaction between the brains of mother and child and thus as the first symptom of schizophrenia, even though the disease doesn’t develop fully until puberty. The same applies to autism, another early developmental brain disorder (see chapter 9) that also often goes hand in hand with birth-related problems. Recent studies have shown that girls who suffer from the eating disorders anorexia and bulimia nervosa often had problems at birth, including low birth weight. The more numerous such problems are, the earlier eating disorders manifest themselves in young adults. One wonders whether their hypothalami started out unable to deal well with glucose levels, given that a decrease in them signals the start of labor. So here, too, birth-related problems of this type could be seen as the first symptoms of a malfunction of the hypothalamus, later taking the form of an eating disorder.
FIGURE 3. When the growing fetus registers that the mother can no longer provide sufficient nourishment, the stress axis in its hypothalamus is activated. Its adrenal gland is stimulated by ACTH to produce cortisol. This reduces the effect of progesterone from the placenta and causes estrogen production to increase. As a result, the uterus becomes more sensitive to oxytocin, activating labor pains and starting the birth process.
A child with a developmental brain disorder can’t fulfill its essential role during labor. Extremely delicate interaction is needed between mother and baby for birth to proceed well. Thinking about birth in this way takes a bit of getting used to because it means that a child’s say in life starts right from birth.
A DIFFICULT BIRTH AS THE FIRST SYMPTOM OF A DEVELOPMENTAL BRAIN DISORDER
When there is no more food for the young in the egg and it has nothing on which to live it makes violent movements, searches for food, and breaks the membranes. In just the same way, when the child has grown big and the mother cannot continue to provide him with enough nourishment, he becomes agitated, breaks through the membranes, and incontinently passes into the external world, free from any bonds.
Hippocrates
In one-third of cases, brain disorders that manifest themselves as a child develops are wrongly ascribed to a difficult birth. In fact, the brain defects that cause such conditions as learning disabilities and spasticity often come into being long before birth.
The English surgeon William John Little is credited as the first person to identify spastic diplegia (a form of cerebral palsy), having described the condition in forty-seven children in 1862. His conviction that it was caused by birth trauma is still held by many to this day. Strangely enough, little attention has been paid to the opposing view held by Sigmund Freud, who, after a careful study in 1897, concluded that a difficult birth couldn’t cause spasticity but that both the neurological condition and the difficult birth should be seen as the consequence of a developmental disorder of the fetal brain. Problems at birth are often also blamed in the case of children with learning disabilities. Prader-Willi syndrome is a genetic disorder that causes morbid obesity over the course of time (see chapter 5). Many children with this syndrome have a difficult birth and go on to have learning disabilities. These aren’t caused by birth-related problems but by the genetic abnormality that was present from conception.
In only 6 percent of children born at due date with spasticity and a mere 1 percent of children with learning disabilities can the disorder be attributed to a lack of oxygen at birth. The vast majority of children with these conditions experience problems long before birth, as is evident from their slow growth and lack of movement in the womb. Spasticity has many different causes, ranging from genetic abnormalities and intrauterine infections to exposure to chemicals, iodine deficiency, and long-term oxygen deficiency in the womb. Conversely, it’s striking that serious brain damage often does not result when a normal fetus is suddenly deprived of oxygen at birth, as Freud already noted. To understand why he was right, you need to be aware of the active role played by the fetus in the birth process. Its brain plays a crucial part, both in initiating labor and during its course. The relationship between a difficult labor and impaired brain function is usually the opposite of what is generally assumed. A difficult labor or premature or delayed labor tends to be the consequence of a problem in fetal brain development. And that deficiency can in turn be caused by genetic factors, lack of oxygen in the womb, infections, or exposure to medication or addictive substances ingested by the mother, like morphine, cocaine, or nicotine. So efforts to establish the cause of premature or difficult birth are incomplete without examining the child’s brain.
That a child’s brain plays a very active role in labor is something we established thirty-five years ago, in a study with the gynecologist W. J. Honnebier. We looked at the births of 150 anencephalic infants (children born with most of their brain missing, fig. 4). Babies with this condition are usually born extremely prematurely or very overdue, and labor proceeds much more slowly than normal. That birth takes twice as long (and the birth of the placenta three times as long) is due to the absence of oxytocin in the child’s brain. Half of these babies don’t survive, which shows how important a well-functioning fetal brain is to the process of labor. Another hormone secreted by the fetal brain, vasopressin, ensures that blood is mainly directed to those organs that are
crucial to survival during birth, like the heart, the adrenal gland, the pituitary gland, and the brain. This involves depriving less vital areas like the intestines. Animal studies have revealed the many complex chemical steps that are necessary for the birth process. But it all starts when a child’s brain registers that the maternal food supply is becoming inadequate, causing it to give the signal for the onset of labor, just as the Greek doctor and philosopher Hippocrates noted over two thousand years ago.
FIGURE 4. An anencephalic newborn, a child born with most of its brain missing. To establish whether the mother’s brain or the child’s brain initiated the birth process, we studied the birth of 150 anencephalic babies. Their births were usually either extremely premature or extremely overdue, the normal precise timing of birth (around the fortieth week of pregnancy) having been completely disrupted. The birth process itself took twice as long as normal, and the placenta took three times as long to appear. In normal circumstances, a baby’s brain determines the moment of birth and speeds up the birth process.
MATERNAL BEHAVIOR
Behold two horses that appear of the same size and shape: How do you know which is the mother and which the son? Give them hay. The mother will nudge the hay toward her son.
The Teachings of Buddha
A woman’s brain starts being programmed for maternal behavior right from the onset of pregnancy. Hormones alter the brain in ways that are reinforced after the birth by the presence of the child. The changes in the mother’s brain are long-term, perhaps even permanent. Adults sometimes lament that the umbilical cord attaching them to their mothers has never really been cut, while mothers can be burdened by concern about their offspring well after they’ve grown up. If something happens to their child, some will claim they felt a premonition the previous day—which is true, for the simple reason that they worry about their children on a daily basis.
During pregnancy the pituitary gland secretes the hormone prolactin, which prompts nesting behavior. There’s an urge to clean the house and paint the baby’s room. Once, when I went to check on my laboratory rats as a PhD student, I was sure that someone had swapped my cages with adult male rats for ones with pregnant rats. Each of the rats had built an enormous nest of sawdust. They were, in fact, my male rats—they had built the nests because the previous day I’d given them a dose of prolactin. Similarly, during his stay in Amsterdam’s Wilhelmina Gasthuis hospital, a male patient with a pituitary gland tumor that produced prolactin was never happier than when helping staff clean the bedside lockers.
At the end of pregnancy, both the mother’s and the child’s brain cells produce oxytocin and release it into the bloodstream. This hormone has many functions. Doctors use oxytocin to induce labor, and some women are given nasal spray containing oxytocin to boost milk release after giving birth. Its role at the end of pregnancy is to stimulate and speed up labor. The mother’s brain secretes more oxytocin at night, when the uterus is most sensitive to the hormone, which encourages labor to start while the body is at rest. During labor, extra oxytocin is released when the child’s head presses down on the cervix. This signal is passed on to the mother’s brain via the spinal cord, triggering the release of more oxytocin to heighten labor. If a woman is given an epidural to offset labor pains, the signal no longer reaches her brain, causing her pituitary gland to release less oxytocin. In such cases women often need an oxytocin drip to restore the strength of their contractions.
After birth, oxytocin ensures that the mother secretes enough milk. When the child sucks at the nipple, it stimulates its mother’s brain to release oxytocin, causing milk to be expressed from the mammary gland. After a time, it’s sufficient for the child to cry to trigger this reflex. Such a strong dose of oxytocin is produced that milk spurts from the breasts—a potentially embarrassing state of affairs in company. Farmers have known about this reflex for centuries, having seen how milk will spurt from the cow’s udders when they come into the cowshed rattling a milk bucket.
Studies are increasingly revealing the importance of oxytocin in many forms of social interaction. One of the new names given to it is the “bonding hormone” because of the tie it creates between mother and child. This process starts in late pregnancy, when oxytocin levels surge, peaking during birth. When delivery is by Caesarean section that peak does not occur, which might explain why the mother’s brain reacts less strongly to the child’s crying and maternal behavior takes longer to manifest itself. Nursing and playing with the child causes the mother’s brain to be calmed by oxytocin, which also stimulates her warm interaction and close bond with the child. A mother who hasn’t formed a close attachment to her child doesn’t experience a rise in oxytocin levels when she plays with it. Children who grew up in an orphanage have lower levels of oxytocin in their blood than children who grew up in a family. Even three years after being adopted, children who were neglected early in their development don’t experience a normal surge of oxytocin during affectionate bodily contact with their carers. In other words, their ability to bond is impaired on a long-term basis, sometimes even permanently. A recent study of women who had been emotionally neglected or physically or sexually abused showed greatly reduced oxytocin levels in their cerebral fluid, causing concern that their problems would be passed on to the next generation. Oxytocin also inhibits the stress axis. When girls between the ages of seven and twelve underwent the stressful experience of giving a talk to a group of strangers, reassuring input from their mothers led to the release of oxytocin. It made no difference whether the child was cuddled or simply reassured by a telephone conversation with the mother.
These findings seem to suggest that it’s possible to inhibit that excessive motherly concern that can be so annoying to adult children. Maternal behavior in apes was experimentally blocked with a substance that inhibited oxytocin’s effect on the brain. It would seem to be the perfect medication for mothers who simply can’t accept the fact that their children can function perfectly well independently. Unfortunately, however, the substance reduces apes’ interest not only in their offspring but also in sex.
Thirty years ago, our research group investigated the effect of oxytocin on the brain and behavior. We created oxytocin antibodies, staining them so that they would show up in the brain, and looked for the locations where oxytocin is produced and secreted. We found extensive networks of brain cells and axons containing oxytocin in a number of brain structures (fig. 5). Those fibers made contact with other neurons, transferring oxytocin to them in the form of a chemical messenger. Examination with an electron microscope revealed that transmission locations looked just like the synapses (cell contact points) where other chemical messengers are passed from one neuron to another (fig. 6). These form the basis for oxytocin’s behavioral effects.
Different social contexts prompt the release of oxytocin in specific parts of the brain, triggering different types of behavior. It has been identified as the messenger of affection, generosity, tranquility, trust, and attachment. Oxytocin has also been found to suppress fear by affecting the amygdala, the center of fear and aggression. When affectionate social interaction like hugging takes place, not only do oxytocin levels in the blood rise but more oxytocin is also released in the brain. It’s also the messenger that tells your brain when you’ve had enough to eat. Oxytocin affects not only maternal behavior but also adult relationships, influencing our responses to social stress and sexual contact. As a result it has been dubbed the “love hormone.” Yet again, this is nothing new to farmers, who have been aware of its effects for centuries, long before anyone had ever heard of the hormone. When an orphan lamb is placed with a foster mother, the farmer stimulates the sheep’s vagina and uterus, causing oxytocin to be released and the ewe to bond with the strange lamb.
The brain also produces a closely related substance: vasopressin. Just like oxytocin, vasopressin plays a crucial role in maternal behavior, including maternal aggression prompted by threats to offspring. It’s also involved in other aspects of social behav
ior, like pair bonding. Men with a tiny variation in a DNA building block for the vasopressin receptor (the protein that receives vasopressin’s message in the brain) are twice as likely to experience marital difficulties and divorce and twice as likely to be unfaithful. If men are shown an image of a strange man after being given vasopressin, they perceive the facial expression as unfriendly, making them more hostile. In the case of women, exactly the opposite occurs. Vasopressin makes them more likely to approach strangers, because they are better at distinguishing friendly features. It’s tempting to imagine how society might be improved by giving men a whiff of oxytocin and women a whiff of vasopressin.
A link has recently been found between autism and malfunctions in the brain’s vasopressin and oxytocin systems. People with autism often find it hard to interpret other people’s emotions and intentions from their gestures and facial expressions or to feel empathy. Some don’t understand what is going on, for instance, when another child cries, or can’t detect emotion in a person’s voice. Temple Grandin, a professor of animal science with autism, has described her emotional circuitry simply as being disconnected. Indeed, abnormal blood levels of vasopressin and oxytocin have been found in people with autism. They also display small genetic variations in the proteins that are the brain’s vasopressin and oxytocin receptors. Conversely, their ability to “read” emotions and predict behavior through facial cues improves when they are given oxytocin. It also helps them to detect emotion in someone’s voice and to grasp the emotional significance of intonation. So both oxytocin and vasopressin can play a part in autism, but to regard these two chemical messengers as the “social brain” is a huge oversimplification. Many more messengers and brain structures are involved in social behavior.