We Are Our Brains

by D. F. Swaab

  There’s no lack of speculation about the mental baggage we bring with us into the world and the influence that our time in the womb allegedly has on the rest of our lives. “Prenatal universities” have been set up in the United States, at which mothers learn to interact with their unborn children. It’s true, your intrauterine history determines your risk of many psychiatric disorders, like schizophrenia and depression. But some therapists go too far when they maintain that traumatic memories from the fetal period are the cause of very specific psychiatric problems later in life. It’s been claimed that some headaches in adult life are due to forceps delivery or pain during childbirth. Some blame women’s obstetric or gynecological problems on a feeling of being unwanted at birth, because they were girls. Others attribute a penchant for bondage to being entangled in the umbilical cord at birth or a fear of being crushed to a long, difficult passage through the mother’s narrow pelvis. Luckily, the same therapists reassure patients that problems like this can easily be solved by regression therapy, the theory being that to identify the cause of your problems is to solve them. A forensic study compared 412 suicide victims who were alcoholics and drug addicts with 2,901 people in a control group. A link was made between events around birth and self-destructive behavior. Suicides by hanging were associated with oxygen deprivation at birth, violent suicides with mechanical birth trauma, and drug addiction with the administration of addictive substances like painkillers during labor. A recent independent Dutch study, however, found no link between opiates administered as painkillers at birth and subsequent addiction. I’m very curious to know the results of future attempts to confirm the other correlations.

  Dalí did not need regression analysis or LSD to remember his intrauterine stay in detail, which he recalled as heavenly. “The intrauterine paradise was the color of hell, that is to say, red, orange, yellow and bluish, the color of flames, of fire; above all it was soft, immobile, warm, symmetrical, double, gluey.” His most splendid memory was of two fried, phosphorescent eggs. Dalí said he could reproduce a similar image at will by pressing on his closed eyelids (“characteristic of the fetal posture”). Those fried eggs return in many of Dalí’s paintings. Indeed, the human fetus does respond to light from the twenty-sixth week of pregnancy. But even if Dalí’s mother had lain in the sun in her bikini during her pregnancy, which is highly unlikely, the little Salvador wouldn’t have been able to observe much more than a diffuse orange glow. So it would seem that detailed visual memories are the privilege of Surrealists.

  However, other types of fetal memory have been demonstrated in a number of species. It’s undoubtedly useful for a baby bird to become familiar with the call of its parents while still in the egg. The same applies to humans: The bond between mother and child is first established during pregnancy through the mother’s voice. The existence of fetal memory in humans has been shown from three experimental paradigms: habituation, classic conditioning, and exposure learning. Habituation is the simplest form of memory, whereby the reaction to a stimulus declines the more it is encountered. In the human fetus, habituation is present as early as the twenty-second week of pregnancy. Classic conditioning has been demonstrated from the thirtieth week. Vibrations, for instance, have been used as the “conditioned stimulus” (akin to the bell in Pavlov’s famous experiment with dogs), while a loud noise has been the “unconditioned stimulus” (akin to the food in Pavlov’s experiment). But the level of the nervous system at which this type of learning takes place is debatable. Since an anencephalic fetus (a baby with most of its brain missing, fig. 4) can also be conditioned in this way, such learning may take place at the level of the brain stem or spinal cord. The experiments to determine exposure learning produced a much more interesting finding: When a pregnant woman relaxed every time she heard a particular piece of music, after a while the fetus began to move as soon as the music started. After birth, the same child stopped crying and opened its eyes on hearing the same music. Hearing the mother’s voice while in the womb could play a role in the development of language and the bond between mother and child. Newborn babies prefer their mother’s voice, particularly if it’s distorted in the way that it would have been in the womb. They can also recognize a story repeatedly read aloud by the mother during pregnancy. However, the fetal memory for sounds has its dangers. Newborn babies show a clear response when they hear the theme tune of television soaps obsessively watched by their mothers during pregnancy. They stop crying and listen alertly to the highly familiar tune, and you wonder whether they are doomed to be addicted to such programs when they grow up. The unborn child’s great sensitivity to melody might also explain why French babies cry with a rising intonation and German babies with a falling intonation, reflecting the different intonation contours of the two languages. Might this be the first expression of musical ability?

  Babies can also remember scent and taste stimuli from the womb. Their mother’s smell is instantly recognized after birth, which may be important to successful breast-feeding. Newborn babies normally dislike the smell of garlic, but if a woman eats garlic during pregnancy, her baby will not be averse to its smell. It is interesting to note that culinary differences between the French and the Dutch go back all the way to intrauterine experiences!

  In sum, the fetus has a memory of sound, vibration, taste, and smell. So it’s possible that we’re ruining our children’s brains not just by smoking and drinking and by taking medicine and other drugs but also by watching bad television programs. In other words, you’d do well to pick up a good book now and again and read to your unborn child in the hope that the next generation will rediscover literature. And that’s not a new idea, by the way, because as far back as A.D. 200–600, the Talmud made mention of prenatal stimulation programs. But memories of the womb aren’t detailed and as far as we know disappear within a few weeks, instead of lasting a lifetime, as some therapists and Salvador Dalí would have us believe.

  2

  Threats to the Fetal Brain in the “Safety” of the Womb

  DEVELOPMENTAL BRAIN DISORDERS CAUSED BY ENVIRONMENTAL FACTORS

  We pollute our children’s amniotic fluid.

  Our brains develop with incredible rapidity before birth and in the years immediately after. Moreover, each tiny area of the brain and each cell type within that area develops at a different tempo. During this period of explosive growth, brain cells are extremely susceptible to a number of different factors. First, for the brain to develop normally, the unborn child needs sufficient nourishment. Its thyroid gland also needs to function properly. At this stage, brain development is determined in general by our genetic background and in detail by the activity of our nerve cells. These, in turn, are influenced by the availability of nutrients, chemical messengers from other brain cells (neurotransmitters), growth regulators, and hormones. At that stage, the unborn child’s sex hormones regulate the sexual differentiation of the brain. Substances that enter the fetal system via the placenta can derail the delicate process of brain development. These can either come from the environment or be ingested by the expectant mother (for instance, alcohol, nicotine, and other addictive substances and medications).

  Sadly, we live in a world in which 200 million children suffer from serious and lasting brain damage due to lack of nourishment. Not only is their mental capacity impaired; they also have an increased risk of schizophrenia, depression, and antisocial behavior. This was shown by a study of children born in the major Dutch cities during the famine (“Hunger Winter”) of 1944–1945 (fig. 9). Even in today’s affluent society the same problem still occurs when a placenta malfunctions, depriving the fetus of nourishment and causing it to be undersized at birth. Malnutrition in the womb can also occur when a pregnant woman vomits excessively, tries to keep her weight down by dieting, or eats too little because of the Ramadan fast.

  Some 200 million people live in regions with an iodine shortage, which affects their children’s growth. Such places aren’t necessarily remote; they can be found all over th
e world. Thyroid hormones are necessary for normal brain development but can only function if sufficient iodine is incorporated into the hormone. This happens in the thyroid gland. In mountainous areas, the iodine found naturally in soil can be washed away by rainwater. The resulting shortage of iodine affects the functioning of a child’s thyroid hormones, leading to impaired brain and inner ear development. Such children develop huge thyroids that desperately try to store every scrap of iodine ingested. In the worst cases, thyroid hormone deficiency results in cretinism, a condition of severely stunted mental and physical growth. The endocrinologist Dries Querido made it his life’s work to find remote places with an iodine shortage. I remember him calling me late one evening to ask if I could get him a sixteen-millimeter film projector for a lecture he had to give the next day in Amsterdam. That was how I became one of the first people to see a film he had shot in the Mulia Valley in New Guinea, then still a Dutch colony—a remote spot that could be reached only by a Cessna airplane—and hear about his expedition’s findings. Around 10 percent of the children in that valley were mentally deficient and deaf and had serious neurological disorders. Querido proved that this was caused by iodine deficiency, and he treated the locals with an injection of Lipiodol, an oil containing iodine. Formerly used as a contrast agent in X-ray photos of the lungs, it was found to be potentially damaging to lung tissue. However, it turned out to be extremely effective as a depot injection to treat iodine deficiency. Similarly, the simple remedy of adding iodine to kitchen salt led to the closure of every single institution for deaf-mutes in Switzerland. In the twenty-first century, I myself witnessed developmental disorders resulting from iodine deficiencies in the mountains of Anhui, China. A woman suffering from cretinism—and disfigured by a huge goiter—was sweeping away leaves at a temple. When one of the members of our team, a Chinese professor, asked the woman if she would like to see a doctor, she merely growled and waved her broom threateningly at us.

  Heavy metals can also disrupt fetal brain development. The lead added to gasoline to reduce engine knocking entered the atmosphere, causing more children to be born with mental disabilities. The dangers of mercury became apparent only in the 1950s, when cats in the fishing villages around the Bay of Minamata in Japan started acting strangely and dying and fish began to swim in bizarre patterns. The fishermen had been selling their best fish and keeping the worst specimens for the family pantry. As a result of the fish’s high organic mercury content—mercury that proved to come from a plastics factory—6 percent of the children in the surrounding villages had suffered serious brain damage before birth. The formation of their brain cells and the growth of brain tissue had been inhibited by the mercury, leading to mental disability. The adults in these villages also developed various forms of paralysis. A monument has now been erected in Minamata’s environmental park, dedicated to all the life-forms in the Shiranui Sea that fell victim to this disaster. The park itself was built on twenty-seven tons of mercury-polluted sludge from the Bay of Minamata as well as dozens of sealed containers full of poisoned fish. The Japanese government never gave the victims proper financial compensation.

  Disorders of sex development, or intersex, are also often caused by environmental factors during fetal development. They affect up to 2 percent of children, depending on how comprehensively you define such disorders and at what stage of life they are diagnosed. In 10 to 20 percent of cases, no chromosomal cause is found for atypical development of the sex organs, so one may conclude that the disorders are due to environmental chemicals. DDT, PCBs, dioxins, and many other substances present in the environment are now referred to as “endocrinal disrupters” because they can disrupt hormonal regulation of sexual differentiation. As far back as 1940, the pilots of planes spraying DDT were found to have reduced sperm counts. What’s more, the effects of these substances on brain development have been demonstrated in many animal species. The possible impact of endocrinal disrupters on the process of sexual differentiation in the fetal brain—and thus on gender identity and sexual orientation (see chapter 3)—is a concern that has arisen only very recently.

  DEVELOPMENTAL BRAIN DISORDERS CAUSED BY ADDICTIVE SUBSTANCES AND MEDICATION

  Are we harming our children’s brains before they are even born?

  Title of my inaugural speech, 1980

  Fortunately, the most severe developmental disorders that can arise early in pregnancy are rare. Examples of such serious birth defects include spina bifida (the risk of which is increased by taking antiepileptic drugs during pregnancy), anencephaly, which is the absence of a forebrain (often associated with exposure to pesticides), or missing limb parts. The latter type of defect occurred in great numbers during the late 1950s and early 1960s after the appearance of a now-notorious sedative drug called thalidomide that was prescribed for pregnant women. It led to a great number of children being born with teratological abnormalities, usually missing limb sections. The thalidomide disaster made doctors more cautious about prescribing medication during the first three months of pregnancy.

  These defects, however, are just the tip of the iceberg of the developmental brain disorders that can be caused by chemical substances during pregnancy, including after the first trimester. Microscopic abnormalities are far more common than classic teratological abnormalities. They occur later in pregnancy only, and the problems they cause manifest themselves much later in life. Children affected in this way appear to be completely healthy at birth, but the defects emerge later, when functional requirements are imposed on their brain systems. The children of pregnant women who smoke, for instance, are much more likely to have learning difficulties as well as behavioral problems in adolescence and reproductive problems in adulthood. These disorders are known as functional disorders or “behavioral-teratological disorders.”

  Many chemical substances can reach the fetus and threaten its developing brain. Heavy metals in the environment, nicotine, alcohol, cocaine, and other addictive substances, as well as medication taken during pregnancy, can disrupt the rapid development of the brain. Children exposed before birth to the drugs taken by their mothers not only display withdrawal symptoms after birth but can also be left with permanent brain damage. I believe that all substances that affect the adult brain can also influence the development of the fetal brain. I have yet to see a single exception to this rule.

  Alcohol

  That alcohol can cause birth defects has been common knowledge for a very long time. The Phoenicians of Carthage apparently worried about the effects of alcohol on unborn children, to judge by their law banning the drinking of alcohol on one’s wedding day. The English writer Henry Fielding warned of the effects of the British gin epidemic back in 1751, lamenting, “What must become of an infant who is conceived in gin?” It wasn’t until 1968 that French scientists established that drinking during pregnancy could impair fetal brain development—rather in the way that Gammas were bred by adding alcohol to the blood surrogate around the developing embryo in Aldous Huxley’s Brave New World (1932). However, the French publication went unnoticed until it was rediscovered in 1973, with its finding dubbed “fetal alcohol syndrome” in English-language medical journals. To this day, a quarter of pregnant women have the occasional glass of alcohol, even though drinking while pregnant can cause children to be born with undersized brains and severe mental disabilities. It’s also responsible for less severe damage, specifically learning and behavioral problems.

  In early development, brain cells are created around the brain cavities. They then migrate to the cerebral cortex, where they ripen and sprout tissue to establish contact with other brain cells. This migratory process of fetal brain cells can be so severely disrupted by alcohol that the cells sometimes work their way through the cerebral membranes and end up outside the brain. Alcohol also permanently activates the stress axis of the unborn child’s brain, increasing the risk of depression and phobia. In hospitals in the 1960s, alcohol was routinely administered intravenously to women at risk of giving birth pr
ematurely. It inhibited contractions, enabling the baby to remain in the uterus longer. At the time, no one was concerned about alcohol coming into contact with a baby’s brain. Whether or not this approach was harmful has never been established.

  Smoking

  The potential harm that can be caused to an unborn child when its mother smokes during pregnancy is frightening. Smoking is the most common cause of neonatal death. It doubles the risk of sudden infant death syndrome (SIDS). A mother who smokes increases her child’s risk of premature birth, low birth weight, impaired brain development, disturbed sleep patterns, poorer school performance, and obesity later in life. Her smoking affects not only her own thyroid function but also that of her child. Her children have a higher risk of ADHD, aggressive behavior, impulsiveness, speech defects, attention problems, and, in the case of boys, impaired testes development and reproductive disorders.

  Around 12 percent of women still smoke during pregnancy. Despite the known dangers, very few are able to give up smoking at this stage. (Incidentally, trying to stop by using nicotine patches is also dangerous for the unborn child—animal studies have shown that nicotine has an extremely harmful effect on brain development. In other words, it’s not just all of the substances in the smoke but also the nicotine itself that causes developmental brain disorders.) If all pregnant women in the Netherlands were to stop smoking, 30 percent fewer children would be born extremely prematurely, underweight births would decrease by 17 percent, and savings amounting to $33 million could be made in health care. Surely that’s an effort worth making for your child?