We Are Our Brains: A Neurobiography of the Brain, from the Womb to Alzheimer's - Couverture rigide

Swaab, D. F.

Couverture rigide

ISBN 10 : 0812992962 ISBN 13 : 9780812992960

Editeur : Random House, 2014

A propos du livre

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Chapter 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.

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.

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.

Présentation de l'éditeur :

A vivid account of what makes us human.
 
Based groundbreaking new research, We Are Our Brains is a sweeping biography of the human brain, from infancy to adulthood to old age. Renowned neuroscientist D. F. Swaab takes us on a guided tour of the intricate inner workings that determine our potential, our limitations, and our desires, with each chapter serving as an eye-opening window on a different stage of brain development: the gender differences that develop in the embryonic brain, what goes on in the heads of adolescents, how parenthood permanently changes the brain.
 
Moving beyond pure biological understanding, Swaab presents a controversial and multilayered ethical argument surrounding the brain. Far from possessing true free will, Swaab argues, we have very little control over our everyday decisions, or who we will become, because our brains predetermine everything about us, long before we are born, from our moral character to our religious leanings to whom we fall in love with. And he challenges many of our prevailing assumptions about what makes us human, decoding the intricate “moral networks” that allow us to experience emotion, revealing maternal instinct to be the result of hormonal changes in the pregnant brain, and exploring the way that religious “imprinting” shapes the brain during childhood. Rife with memorable case studies, We Are Our Brains is already a bestselling international phenomenon. It aims to demystify the chemical and genetic workings of our most mysterious organ, in the process helping us to see who we are through an entirely new lens.
 
Did you know?
 
• The father’s brain is affected in pregnancy as well as the mother’s.
• The withdrawal symptoms we experience at the end of a love affair mirror chemical addiction.
• Growing up bilingual reduces the likelihood of Alzheimer’s.
• Parental religion is imprinted on our brains during early development, much as our native language is.

Praise for We Are Our Brains
 
“Swaab’s ‘neurobiography’ is witty, opinionated, passionate, and, above all, cerebral.” —Booklist (starred review)
 
“A fascinating survey . . . Swaab employs both personal and scientific observation in near-equal measure.” —Publishers Weekly (starred review)
 
“A cogent, provocative account of how twenty-first-century ‘neuroculture’ has the potential to effect profound medical and social change.” —Kirkus Reviews

À propos de cette édition

• Éditeur: Random House
• Date d'édition: 2014
• ISBN 10: 0812992962
• ISBN 13: 9780812992960
• Reliure: Relié
• Nombre de pages: 448