by D. F. Swaab
There would seem to be considerable scope for capitalizing on our knowledge of the effects of these substances. Psychological experiments with games involving financial payment have shown a link between high oxytocin levels and trust in others, including strangers. That trust remains even if you get cheated a few times. The commercial potential was immediately spotted, and you can now buy “Liquid Trust” online, little bottles of oxytocin that you spray on your clothes to induce confidence in your partner, boss, co-workers, and customers. Since you can only expose people to very tiny amounts in this way, this is at best a placebo (acting via the person who has sprayed the compound on his clothes), if not a downright rip-off.
It’s also debatable whether a direct dose of oxytocin in the form of nasal spray can replicate the normal brain processes. After all, the brain produces very precise and limited amounts of oxytocin at a very specific location in response to certain circumstances. Just inhaling the substance may have a completely different effect. And that’s actually a general problem when treating disorders of the brain. You can’t replace the highly specialized functions of nerve cell systems just by administering their messengers, any more than you can replace a calculator by means of the figures that it produces.
FIGURE 5. The localization of oxytocin and vasopressin in the brain. The two hormones are produced in two regions of the hypothalamus, the paraventricular nucleus (PVN) and the supraoptic nucleus (SON), and released into the bloodstream as neurohormones in the posterior pituitary. Oxytocin causes contractions of the uterus during labor and contractions in the mammary gland during suckling. Vasopressin regulates the body’s retention of water by acting on the kidneys. Oxytocin and vasopressin are also transported to many brain areas that we know of (indicated here with abbreviations) and to as yet unknown brain areas, and are released in those locations from synapses as neurotransmitters (chemical messengers).
PATERNAL BEHAVIOR
A son can never show sufficient gratitude to his parents for their loving kindness, even were he to carry his father on his right shoulder and his mother on his left shoulder for 100 long years.
The Teachings of Buddha
We all know cases of mothers who just haven’t managed to sever the umbilical cord. Their children might be long grown up, but they are constantly concerned about them and want to know exactly what they are doing, even when they’re on the other side of the globe. The tie between mother and child remains a special one. No matter what country he fights for, a wounded soldier on a battlefield will always call for his mother, not his father.
In the case of chimpanzees, females are responsible for teaching cultural skills. So I always thought that a father’s role was confined to fertilization, the moment at which less than half the child’s DNA has to be delivered, a job that can be done in a few minutes. We fathers could then hide behind the newspaper and leave the child’s care and upbringing to the mother. But it turns out that fathers can’t get off that lightly. The animal kingdom provides examples of paternal behavior that replicate every aspect of maternal behavior. There is even a male bat that produces milk!
Humans do occupy a special place in the animal world in terms of their focus on the family. The family is the building block of our society, which is not the case with great apes like chimpanzees or bonobos. It’s not so much pair formation that’s unusual—you see that in gibbons, birds, and voles—but in those species families live isolated from each other. The family-based society is unique to our species. As far back as two million years ago, our ancestors gave birth to offspring that weighed twice as much as those of chimpanzees. Since those heavy, helpless babies couldn’t be transported easily, shared child care was crucial to ensure sufficient food for the mother and a chance for her to suckle her offspring. Patriarchy—male dominance within the family—is thought to have developed when our ancestors had to exchange the protection of the jungle for a more vulnerable life in the savanna. In those wide-open spaces it was crucial for the male to protect the female and her child. Incidentally, these human ancestors, who walked on their knuckles, ate fruit, hunted, and used tools, didn’t leave the jungle of their own volition, as is so often claimed. The jungle disappeared around them as a result of drastic climate change. Vast tracts were gradually transformed into dry savanna. The male’s protection of the female and her child had an evolutionary advantage: Humans were able to reproduce every two to three years, while female chimpanzees, who were solely responsible for their young and therefore had to look after them and feed them for much longer, could reproduce only every six years.
That protective role of the male isn’t confined to primates but extends to the entire animal kingdom. A pair of coots have once again built a large nest in the middle of the canal opposite our house. From the moment that the female started to sit on the nest, the male became incredibly aggressive toward any other birds in the vicinity. Not a single egg had yet been laid, but the coot managed to scare off much larger crows and ducks with a great deal of noise and flapping of wings.
A man, too, is prepared for his role as a father during his partner’s pregnancy. Hormonal changes take place that affect the brain, making prospective fathers not only behave differently but also feel differently. Even before the child is born, the father’s prolactin level increases. That hormone is important for the mother’s milk production, but in both women and men it stimulates caring behavior. Conversely, the father-to-be’s level of the male sex hormone testosterone declines, reducing aggression toward the child and the urge to procreate—a universal mechanism that affects prospective fathers from New York to Beijing. As a result, even before their child is born, many men feel that something special is happening to them. How those behavioral changes are induced isn’t clear, but scents given off by the pregnant partner may play a role. After the birth, prolactin and oxytocin play a role in paternal behavior and bonding between father and child. When playing with their children, an increase in the bonding hormone oxytocin is seen only in fathers who display affectionate and nurturing behavior.
In some animal species, the father has been allotted an extreme role. In the case of the Greater Rhea, an ostrich-like bird, the males incubate the eggs in a nest that they have scraped out themselves, while male seahorses carry their eggs in a pouch until they hatch. Caring paternal behavior comparable to that of humans is seen in a few other species, allowing us to study the changes in the brain that provoke it. Marmoset fathers look after their offspring by carrying them, protecting them, and feeding them. Fatherhood induces changes in the prefrontal cortex. The number of synapses in this area of the brain increases, suggesting a reorganization of the local network. It also becomes more sensitive to vasopressin, the chemical messenger that promotes social behavior and aids fathers in their new tasks.
As children grow up, their fathers may inspire them and affect the course of their lives. This can take many different forms. My grandfather was a doctor, and he succeeded in interesting his son in his profession. My father became a gynecologist, and I knew from the age of six that I would study medicine. My son was uncertain about his choice of studies for a long time, but he knew from an early age that it would not be medicine or biology. He, too, was reacting to his father, albeit in a different way. We later discovered a shared interest in behavioral differences between the sexes and both published findings on this subject (see chapter 21).
Alas, the father’s role doesn’t confine itself to noble actions like care, protection, and inspiration. Examples of the primitive aggression that males are capable of in the name of fatherhood are common both in the animal kingdom and among humans. Male primates can take over an entire harem of females from another group by chasing away the dominant male. As a rule, they then kill all the young. When a lion takes over a pride of lions, he kills the cubs, despite the lioness’s desperate attempts to defend them. This stops her milk production, making her fertile more quickly, ensuring that her young are the offspring of the new dominant male. And human history shows us
to be no exception, to judge by what we read in the Bible: “But Moses was angry with the officers of the army, with the captains … who had come from the battle [and] said to them: ‘… Now therefore, kill every male among the little ones, and kill every woman who has known a man intimately. But keep alive for yourselves all the young girls who have not known a man intimately’ ” (Numbers 31:14–18).
Even in this day and age, we haven’t yet managed to escape these cruel biological mechanisms. Infanticide and child abuse are more commonly perpetrated by stepfathers than biological fathers, and children of women captured during wars are still regularly killed. Female chimpanzees keep far away from groups of other chimpanzees for years after giving birth—a good strategy for ensuring that their young aren’t killed by males who doubt their paternity. The “solution” devised by bonobo females to prevent infanticide is an original one. They mate with all males, so that no single male can ever be certain that he’s not a youngster’s father. But in the case of humans, mothers must remain vigilant, alert to all the dangers that might threaten their children—a state they remain in for the rest of their lives.
FIGURE 6. A synapse as seen under an electron microscope. Oxytocin and vasopressin appear as black granules. When released in the brain, these substances influence behaviors—for instance, social interaction. From Buijs and Swaab, Cell Tiss. Res. 204 (1979): 355–65.
THE IMPORTANCE OF A STIMULATING ENVIRONMENT FOR EARLY BRAIN DEVELOPMENT
A good environment is not a luxury, it is a necessity.
R. Wollheim
You come into the world with a brain that your genetic background and your development in the womb have made unique and in which your character, talents, and restrictions have largely been determined (see chapters 3 and 8). For the brain to grow optimally after birth, the developing child needs a safe, stimulating environment that imposes achievable demands on it. Back in 1871, Darwin had already found that the brains of hares and rabbits that grew up confined in boring hutches were 15 to 30 percent smaller than those of their wild counterparts. Conversely, when animals are placed in an “enriched environment,” a large enclosure full of objects that are renewed each day and in which they can play with one another, their brains grow and develop more synapses. Children who are seriously neglected during their early development also have smaller brains (fig. 7); their intelligence and linguistic and fine motor control are permanently impaired, and they are impulsive and hyperactive. Their prefrontal cortices can be particularly undersized. Studies have shown that orphans adopted before the age of two go on to develop normal IQs (averaging 100), while children who are not adopted until between the ages of two and six attain average IQs of 80.
The American child psychiatrist Bruce Perry described the case of a grossly neglected six-year-old boy named Justin, who lost his mother and grandmother as a baby and grew up in the care of a dog breeder, who treated him like one of his dogs, keeping him in a cage. He made sure that Justin was fed and changed, but he hardly spoke to him and never cuddled him or played with him. When Justin was later hospitalized, he was unable to speak or walk. He threw his feces at the medical staff. A scan showed his brain to be much too small; it resembled that of someone with Alzheimer’s. In the stimulating environment of a foster family, he started to develop, and by the age of eight was able to go to nursery school. It isn’t known what lasting damage he has suffered.
In his book Émile; or, On Education, published in 1778, the Enlightenment philosopher Jean-Jacques Rousseau (1712–1778) set out his theory of the “noble savage.” He believed that children were innately good but were subsequently corrupted by society. However, interaction with one’s surroundings is necessary for normal brain development, as is clear from Justin’s story and the well-documented tale of the Wild Boy of Aveyron, a feral child discovered in the woods of the region of Languedoc in southern France in 1797. It took three full years before the child was captured by hunters and brought to the local town. At the time he was around ten; having been abandoned at a very young age, he had kept himself alive on a diet of fruit and small animals. A young doctor, Jean Marc Gaspard Itard, took on the task of educating the boy (whom he named Victor), sending lengthy reports on his progress to the French government department for internal affairs. Despite Dr. Itard’s best efforts, Victor never developed fully as a person, and the only word he learned to say was lait (milk). It makes one wonder about the achievements of those other famous feral children, Romulus and Remus.
The acquisition of our mother tongue also shows how certain brain systems continue to be programmed by the environment after birth. A child’s first language isn’t determined by its genetic background, only by the surroundings in which it grows up during that critical period of language acquisition. Not only does acquiring language have a very marked effect on the brain, it’s also crucial to many other aspects of a child’s development. In 1211, the Holy Roman Emperor Frederick II of Germany, Italy, Burgundy, and Sicily tried to establish what language God spoke to Adam and Eve. He believed that children would spontaneously speak it if they were not exposed to other languages and set up a rigorous experiment in which dozens of children were brought up by nurses ordered never to speak to them. However, his hopes were met with disappointment. The children couldn’t speak at all, and they all died at a young age. Likewise, one in three orphans brought up in severely understaffed children’s homes in World War II died from the consequences of physical and emotional neglect, and those who survived were psychologically scarred. So proper interaction with one’s surroundings isn’t just a precondition for normal brain development, it’s actually crucial to survival.
During the first few years after birth, our surroundings determine the configuration of the brain’s language systems. After a certain critical period these systems become fixed. Any attempts to learn a second language are made with, say, Romanian, Uzbek, Dutch, or Italian brains, causing us to speak with an accent. In children between the ages of nine and eleven, the brain areas that process words and visual information still overlap. By adulthood, specialization has taken place, and the two types of information are processed in separate areas. The language environment creates permanent differences in brain structures and functions. Depending on whether your mother tongue is Japanese or a Western language, vowels and animal sounds are processed in the left or right cortex, irrespective of your genetic origins. The frontal cortex is the site of Broca’s area, which is crucial for language (fig. 8). When adults learn a second language, another sub-area of this region is involved. But if children are brought up bilingually from an early age, both languages use the same frontal areas. In such cases, the left caudate nucleus (fig. 27) checks which language system is being used.
Our linguistic and cultural environments don’t determine only which brain systems are involved in language processing but also how facial expressions are interpreted and how we scan images and their surroundings. Japanese and New Guineans, for instance, find it difficult to distinguish between a face expressing fear and a face expressing surprise. When surveying a scene, Chinese individuals, unlike Americans, don’t focus on a single object at a time but look at it in relation to its surroundings. When doing mental arithmetic, the Chinese use different parts of the brain than Western Anglophones. Both use the same Arabic numerals and the lower region of the parietal lobe (fig. 1), but English speakers make more use of language systems to process numbers, while Chinese speakers make more use of visual motor systems. This can be explained by the fact that Chinese grow up learning characters. (The Chinese abacus is no longer so influential in modern China.)
The notion that the environment stimulates brain development was suggested early on by Maria Montessori, who discovered a link between socioeconomic environment and brain development, which she described in her Handbook (1913). Socioeconomic status is also an important factor in stimulating the development of children with a disadvantage, like being underweight at birth. A highly stimulating “enriched” environment promotes r
ecovery after a developmental brain disorder. Studies have shown that children whose early development is disrupted by malnourishment or emotional neglect can improve radically if placed in a more stimulating environment early on. Children with Down syndrome, too, respond well to intense stimulation in their environment. So children with learning disorders should not be incarcerated in institutions where they receive little stimulation. On the contrary, they have an extra need for stimulus, which will positively affect the rest of their lives.
FIGURE 7. On the left, a scan of the brain of a three-year-old child who was brought up normally. On the right, the brain of a three-year-old child who was severely neglected. The neglected child has a much smaller brain, with larger ventricles (the brain cavities, shown in black). There are also much larger spaces between the convolutions of the brain due to shrinking of the cerebral cortex. Based on B. D. Perry, 2002.
FIGURE 8. Broca’s area (frontal, associated with the ability to speak) and Wernicke’s area (temporal, associated with the ability to understand language). These centers are also closely involved in processing music and singing. Music and language are very much interrelated.
MEMORIES FROM THE WOMB
When Elizabeth heard Mary’s greeting, the baby leaped in her womb.
Luke 1:41
The brain circuitry necessary for our memory matures only in our first years of life, and conscious memories mostly start from the age of two. There are exceptions; some people have very detailed, verifiable memories of events that go back further. But the general absence of memory prior to the age of two doesn’t mean that information from the outside world doesn’t penetrate a child’s brain. It’s a fact that unborn babies respond to external stimuli, but their ability to retain memories from this time hasn’t been demonstrated. Are we indeed born as a tabula rasa, a blank slate, as the early Enlightenment philosopher John Locke thought, or with a treasure trove of memories of the best time of our lives, as the painter Salvador Dalí would have us believe?