SHE was still a fairly new graduate student at Tulane University in New Orleans, Louisiana, when her mentor handed her a paper. “As I skimmed it, I realised it was about cognitive impairment associated with pregnancy and motherhood,” she says. “I also realised no one else had been given the paper.”
Katherine Tombeau Cost was several months pregnant at the time, so her mentor intended the paper to be a joke between friends – but it got her thinking. It’s widely assumed that pregnancy and motherhood turns women into sieve-brained shadows of their former selves: the condition variously called “mummy brain” or “baby brain” is a familiar staple of popular culture. But when Tombeau Cost started digging through the scientific literature, she found little evidence to support it. Indeed, she found evidence to the contrary – at least in rats, which become mentally sharper after giving birth. “There had to be another side of the story,” she says. So she set out to find it.
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The picture that is emerging tells a very different story about “baby brain”. The research also holds promise for understanding postnatal depression, and even factors that contribute to healthy brain ageing in all women. Busting the myth, then, could advance society in more ways than one.
It’s true that pregnant women and new mothers often report cognitive problems. In surveys, up to four-fifths of pregnant women report that they have more trouble remembering phone numbers or stringing a complex sentence together than before they got pregnant. Those results appeared to be bolstered by a widely cited 1997 study revealing that women’s brains shrink by up to 7 per cent over the course of a pregnancy.
All this would have been news to Craig Kinsley. It was watching his wife and newborn daughter that started Kinsley, a neuroscientist at the University of Richmond in Virginia wondering about cognitive improvements brought on by motherhood. “I watched her with the baby, and she knew almost instinctively what to do. And I watched her doing everything she did before – working and now also taking care of the baby,” he says. “It got me thinking: from a rat standpoint, what changes would benefit a mother rat?”
That was what led Kinsley to do the research that later attracted Tombeau Cost’s interest. In his years of studying the neurobiology underlying social behaviours in rats, his animals had never shown any evidence of baby brain. Quite the opposite, actually. Although rats in the final phase of their pregnancy show a slight dip in spatial ability, after their pups are born they surpass non-mothers at . Mother rats are also much faster at catching prey. In one study in Kinsley’s lab, the non-mothers took nearly 270 seconds on average to hunt down a cricket hidden in an enclosure, whereas the mothers took .
A new wave of research, by Kinsley’s team and others, is now also showing that mother rats are bolder. Placed in a stressful situation, they show less fear and anxiety, have lower levels of stress hormones in their blood, and display , such as the amygdala.
What underpins these dramatic changes? Kinsley and his colleague Kelly Lambert at Randolph-Macon College in Ashland, Virginia, believe it is the tide of hormones unleashed during pregnancy, including oestradiol, which soars to levels hundreds of times higher than normal. Then there’s oxytocin, which primes the brain to transform rapidly in response to sensory stimulus from the pups: areas involved in memory and cognition undergo major changes in rat mothers, forging .
Pregnancy and motherhood prompt a number of changes in women’s brains, according to recent MRI studies. Quite why the brain shrinks during late pregnancy isn’t well understood, but this shrinkage is now known to be temporary. By about six months after a woman gives birth, her brain will have regained its original size. But that’s not the end of the story. Between about three weeks and four months after birth, some regions bulk up: including those that play a role in reasoning and judgement, empathy and regulating emotions (see diagram).
In adults, such rapid changes in grey matter normally occur only as a result of major events like illness or brain injury. It just goes to show that “pregnancy is not just some minor event”, as Kinsley puts it. “These changes represent a separate developmental period every bit as important as sexual differentiation or puberty.”
But do they lead to the same kinds of emotional and cognitive improvements found in rats? in Orange, California, has found that, as in rats, women in the last trimester of pregnancy tend to be much less stressed. This is down to a dampening of the hypothalamic-pituitary-adrenal axis, the system responsible for the flight-or-fight response. These changes appear to last beyond pregnancy, although for precisely how long remains unclear.
Intriguingly, human mothers also become more aggressive than non-mothers when provoked ().They also become bolder and more . This all makes evolutionary sense, says Lambert, because a tough mother would better protect her offspring, and a blunted stress response would make her more resilient and able to cope with the many demands of her baby. This benefits her child in more ways than one, as severe maternal stress during and after pregnancy has been shown to harm the baby’s physical and mental health.
Brain boost
However, the similarities with rats end there. Lab experiments generally have not found women’s cognitive performance to be during pregnancy or early motherhood, either in spatial reasoning or memory. The few reliable results that do show a dip relate to verbal memory, and in the few months after giving birth, but it is as slight as it is temporary. This is probably a consequence of the major brain changes that takes place during pregnancy, says Glynn.
So, intrigued by Kinsley’s rat research, Tombeau Cost set out to discover whether maternity might improve women’s spatial ability. She gave pregnant women, breastfeeding mothers and women who had never been pregnant a host of challenges designed to replicate the rat work. For example, to emulate the maze task, Tombeau Cost put women into a virtual pool of water to find a hidden platform on which to rest. She painstakingly measured the distance the women travelled, the time it took them to find the platform, and a host of other factors.
Her results, , were consistent with all the earlier work on humans: no matter how she did the experiment, she found neither impairments nor improvements in the women’s spatial ability.
“Women became bolder and more emotionally resilient after giving birth”
The reason, when she finally saw it, was blindingly simple: of course the skills motherhood boosts in women won’t be the same ones it boosts in rats. Female rats raise pups alone, without help from the fathers or other rats. Boosts in spatial awareness and memory help her find food and get back to her pups speedily. Humans evolved to live in groups, so mothers don’t face the same evolutionary pressures.
So what brain changes would help a human mother raise her infant? It’s early days, but experiments are yielding clues. Starting in late pregnancy, women get better at detecting , though their ability to detect surprise and positive emotions such as happiness doesn’t change. This makes sense, says Glynn: “If you’re trying to protect your infant, you want to be able to detect a threat.”
Motherhood may also make women more strategic, helping them take the demands of having a baby in their stride with little or no impact on the way they cope with existing pressures in their lives. As yet, there are no studies probing this, but Lambert and her colleague Massimo Bardi are designing new experiments. They are intrigued by research on owl monkeys, showing that mothers are better than non-mothers at identifying big stores of food and . There’s a good chance that this research will generalise to humans, not just because we are primates too: unlike rat dads, owl monkey fathers contribute equally to the raising of the offspring.
Glynn is also leading work to fill in some of these gaps. For example, she is giving a group of pregnant women a battery of tasks designed to investigate abilities such as strategic planning and multitasking, and will follow their performance for at least a year after birth.
Our lack of understanding of the full impacts of motherhood on the brain is a sore point for her. “In my opinion it’s almost a crisis in women’s health,” she says. “How can we not know the answers?”
That’s because the implications of baby brain go far beyond a bit of fuzzy thinking. . In the UK, suicide is one of the leading causes of death in new mothers. Abnormal levels of hormones associated with pregnancy may be to blame. In proper amounts, these are critical for fetal development and other aspects of the pregnancy. For example, corticotropin-releasing hormone – secreted by the hypothalamus – rises dramatically during pregnancy, which seems to play a role in making the mother-to-be feel less stressed. But an abnormal spike in its levels is , Glynn has found. A better understanding of the maternal brain and of what hormone levels are beneficial could improve our strategies to prevent the condition.
It could also augment our understanding of the factors that contribute to healthy brain ageing. Research on the impacts of pregnancy on a woman’s health later in life is just beginning, but Liisa Galea at the University of British Columbia in Vancouver, Canada, has found evidence that . “It shouldn’t be surprising that researchers are seeing long-lasting effects of motherhood,” she says.
For Kinsley’s rats, the cognitive improvements lasted well into old age. “We’ve looked at animals up to 2 years of age, which for rats is equivalent to a woman in her mid-80s,” he says. “They still learn more quickly, they’re faster on their feet, and their brains are healthier than in a virgin animal at that age.” Neuroscience backs up these behavioural findings: the brains of older rat mums look healthier than those of non-mothers, containing fewer deposits of amyloid precursor protein, which in humans is linked to Alzheimer’s.
However, the evidence from work in humans is contradictory. One study finds a correlation between . Other work, by Glynn and collaborator Molly Fox, suggests that breastfeeding may protect against Alzheimer’s – as could more pregnancies.
Future studies can unpick these contradictions, says Fox, if they look specifically at the role of maternity hormones on Alzheimer’s. There may be more than just hormones involved – a baby’s cells could be invading the mother’s brain to grow new neurons. Either way, a better understanding of pregnancy’s effects on women throughout their lives could unlock new strategies to reduce the risk of the disease.
A better grasp of exactly what changes occur with motherhood could even improve our understanding of human evolution, says Glynn. “A reptile that lays eggs and leaves them – you don’t see a lot of complexity in that brain,” she says. Evolving new ways of raising offspring required more neural energy and behavioural changes. Did this new repertoire of behaviours increase the complexity of the animals, or vice versa? “This is profoundly important stuff,” she says.
Myth-busting
Busting the myth of baby brain once and for all might also have practical consequences. Plenty of policies are in place to prevent discrimination in hiring practices and protect a woman’s right to return to work after having a baby. However, they don’t address underlying prejudices.
“The idea of ‘baby brain’ seems to be prevalent,” says Tombeau Cost. For example, she has found that women who have never been pregnant than pregnant women or those who have had children. How much of this is a consequence of cultural priming and stereotypes that influence women’s perceptions of their own brainpower? And what about the chronic sleep deprivation that accompanies the earliest stages of parenthood? This has been shown to have similar effects on brain functioning as drinking alcohol.
Tombeau Cost hopes the new research will assure women – and their employers – that underneath it all, their brains are just fine.
Maybe better than fine. The research into the cognitive benefits of motherhood could make women of childbearing age an attractive hiring prospect for employers, rather than a potential liability. For example, the improved threat detection would offer particular advantages in some types of jobs, says Kinsley: “consider fighter pilots and astronauts.”
Lambert is uniformly positive. “Being able to be more efficient in your decision-making, being emotionally resilient, maybe being able to engage in different strategies to solve a problem: that sounds like a wonderful executive or manager to me,” she says.
This article appeared in print under the headline “The real baby brain”
