Bruce Hood - The Domesticated Brain - A Pelican Introduction (Pelican Books)

The depleted levels of cortisol in the chronically stressed mothers were to be expected. But what was unexpected was the plight of their unborn children. One year after the attack, infants born to the mothers who had developed PTSD also had abnormal levels of cortisol compared to babies of other mothers who did not develop the disorder after witnessing 9/11. Vulnerable mothers had passed something on to their children. As Yehuda put it, children of PTSD victims bore ‘the scar without the wound’. 8

It is well known from various disease models that events early in development can have consequences later in life. There is a whole category of substances known as teratogens (literally, ‘monster makers’) that, if the pregnant mother is exposed to them, can result in birth defects. Various drugs, both legal and illegal, as well as environmental toxins such as radiation or mercury can damage the unborn child. However, some diseases resulting from harmful substances take decades to manifest. My own father-in-law died from mesothelioma, a rare form of lung cancer that was probably caused by exposure to asbestos when he was growing up as a child in South Africa. Toxins that enter our bodies can alter the functions of our cells but lie dormant for years. Over a lifespan we may replenish our cells many times, but each reproduction of the cells can carry genetic time bombs that lie in wait for the right circumstances to kill us. Physical substances like asbestos from the environment are obvious candidates as being poisonous to our systems, but what about exposure to psychological toxins? How can our mind’s reaction to non-physical events, such as watching something horrific, produce long-term consequences? How could a mother’s stress in response to 9/11 cross over to the next generation? What could she possibly pass on to her unborn child?

Jerry Kagan, a Harvard developmental psychologist, reckons that around one in eight babies are born with temperaments that make them highly irritable, which is due to their over-reactive limbic systems. They startle easily and respond excessively to sudden noises. 9The limbic system mobilizes the body for action and its circuitry includes the amygdala. It triggers a cascade of hormones and neurotransmitters that prepare the body to respond to threat. Reactivity of the limbic system is a heritable trait meaning that it can be passed on to the child in the genes they inherit. 10These are the highly-strung children who find uncertainty and strange situations upsetting. Depending on how they react to sudden sounds as a four-month-old baby, you can even predict personality many years later. 11Reactivity is like a disposition, which makes some of us twitchy, but others are born more laid-back and chilled. Maybe mothers who developed PTSD after 9/11 gave birth to babies with a nervous nature because of their genes.

Yehuda thinks not. She found that the lowered cortisol effect was only present for those mothers who were in the third trimester of their pregnancy, so it could not just be the genes working alone. There seems to be a critical period when exposure to stress alters the child’s development. To begin to understand how such a maternal impression restricted to a window of vulnerability could possibly happen, we need to look at the history of difficult childhoods and the way that they affect how we respond to stress as adults.

War child

World War II disrupted normal life for thousands of families. In Europe, many children were separated from parents by the turmoil and ended up in institutions. Even though they were generally cared for, many of them grew up into socially impaired and delinquent teenagers. To explain this, John Bowlby, a British psychiatrist, proposed that these children had missed out on a critical phase in development that he called attachment . 12Bowlby believed that attachment was an evolutionary adaptive strategy to form a secure, nurturing bond between the mother and her infant. This early experience not only protects the vulnerable child, but also provides the necessary foundation for coping mechanisms to deal with problems later in life. Without this early secure attachment, the child would grow up psychologically impaired.

Bowlby was inspired by the ornithological work of Konrad Lorenz, who had shown that many bird species form a close-knit bond between mother and chicks. 13This attachment begins with imprinting, where the young chicks will pay special attention to and follow the first moving thing they see. Famously, Lorenz demonstrated that he could make baby goslings imprint on him by incubating the eggs and hand-rearing the chicks when they hatched. In the wild, imprinting was critical for survival by maintaining the proximity of the chicks to the hen, which is why the chicks would imprint to the first moving thing, usually the mother. Investigation of the chick brain revealed that it is innately wired to follow some shapes more than others and that chicks quickly learn the distinct features of their own mother, to tell her apart from others.

Human infants also pay special attention to face patterns at birth and very quickly learn their mother’s face. 14However, primate, and in particular human, early social attachment is unlikely to be as rigid as bird imprinting. Whereas the need to imprint in birds has to be satisfied fairly quickly, primates can take a bit longer to learn to know each other. Another important difference between birds and babies is that humans are not up and running about for at least a year. Whenever the human infant needs their mother, they simply have to cry, which will soon send most mothers scurrying to their infant’s side. A distressed infant’s cry is one of the most painful things to hear (which explains why crying babies on aeroplanes can be so upsetting for everyone around them). This ‘biological siren’ ensures that babies and mothers are never that far apart. 15Infants from around six months of age show separation anxiety when physically separated from their mother, a state characterized by tears and stress as signalled by the rise in cortisol levels in both the infant and mother. These levels eventually return to normal when baby and mother are reunited. 16

With time, both mother and baby learn to tolerate further episodes of separation, but the mother remains a secure base from which the toddler can explore their surroundings safely. Imagine Bowlby’s securely attached toddlers as baseball or cricket players: they feel secure when they are touching the bases or while behind their creases, but become increasingly anxious and insecure as they step farther and farther away from them. Without secure early attachment, Bowlby argued that children would never learn to explore novel situations and develop appropriate coping strategies. They would also fail to become properly domesticated, which was why he believed that children separated from their nurturing parents during the war grew up to become delinquent teenagers.

The lost children

Inspired by Bowlby’s work on social attachment and later psychological abnormality, Harry Harlow in the US set out to test an alternative explanation for the long-term effects of deprived childhoods. 17Maybe children were simply not looked after or given adequate nutrition if they were raised in institutions. If you gave them food and warmth, they should be fine. To test this, he conducted an infamous series of studies where he raised baby rhesus monkeys in isolation for differing amounts of time. Although these infant monkeys were well fed and kept in warm, safe environments, they were left alone. This social isolation had profound effects on their development. Monkeys with no social contact as infants developed a variety of abnormal behaviours as adults. They compulsively rocked back and forth while biting themselves, and when they were finally introduced to other monkeys, they avoided them entirely. When the females from this group reached maturity, they were artificially inseminated to become mothers, but they ignored, rejected and sometimes even killed their own offspring.