‘Pregnancy brain’ and its postnatal relative, ‘mummy brain’, are supposed to be common, if unwelcome, side effects of childbearing. However, while women do report memory lapses or trouble concentrating during pregnancy – imagine putting your lunch in the filing cabinet and your papers in the fridge – this might not be the whole story. In some cases, ‘mummy brain’ may well boost cognitive ability after childbirth.

The actual biology behind ‘mummy brain’ is still largely under-explored, with notable exceptions, including a feature earlier this month in New Scientist. This is set to change, though, and a breakthrough in understanding pregnancy’s effects on brain function could be a medical godsend for the 10 per cent of new mothers in the UK suffering from postnatal depression. We are also long overdue for a cultural breakthrough: assuming that having children is bad for the brain is simplistic at best and harmful at worst.

It’s true that there is scientific evidence for memory impairment during pregnancy. Most of this relies on standard memory tests, and while not all the results are completely clear, pregnant volunteers tended to have more trouble with some tasks (such as verbal memory) than the control groups. Back in 1997, New Scientist itself published an interview with a research group who found that overall brain volume actually shrank during pregnancy – although the researchers also pointed out that brain size quickly returned to normal afterwards.

Unfortunately, these studies focus exclusively on pregnancy; that is, they don’t look for long-term changes in brain function that continue after childbirth. One exception was a 2014 study of memory function in both pregnant and postpartum women. It claimed to find no evidence of memory problems, but this is difficult to interpret because none of the women had been given memory tests before becoming pregnant. Also, some of the muddle-headedness attributed to ‘mummy brain’ probably results from independent physiological stress, which is difficult to control in a clinical study. Living with a newborn often involves a chronic lack of sleep – and sleep deprivation turns anyone’s brain to mush, children or not.

Meanwhile, there is more and more evidence from behavioural studies in animals that reproduction actually increases brainpower. In rodents, for example, females with offspring are better at learning and problem solving than females that have never given birth, with one 2014 study finding that maternal rats are more efficient predators. This makes sound evolutionary sense, since an enhanced ability to catch dinner would help to ensure the offspring’s survival.

For female rats at least, the presence of offspring acts like an ‘enriched environment’, providing a source of novel experience to stimulate neural activity and challenge cognition (which, unsurprisingly, sounds exactly what young children do to their parents). The biology behind this is thought to involve a process called ‘reproduction-induced neuroplasticity’, where nerve cells in the brain start forming new connections. Hormone levels also play a role, even after birth: a 2008 study of owl monkeys found that parents performed better on memory tests and adapted better to new situations than non-parents. These behaviours correlated with changing levels of the hormones DHEA and cortisol, which regulate stress and the ability to cope with change.

Interestingly, the male parents underwent exactly the same hormonal and behavioural changes as the females, perhaps because both male and female owl monkeys help care for their offspring.

So it turns out that the old cliché of ‘mummy brain’ is inadequate. Pregnancy and childrearing seem to have lasting effects on the brain, but at least some of these effects may enhance cognitive functions essential for all aspects of life. Higher-order cognition and enhanced problem-solving abilities are, after all, equally at home at the CEO office as they are in the nursery.