Brain Myths

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The Truth About the Effect of Pregnancy on Women's Brains

Pregnesia is the price paid for what ultimately is a maternal neuro-upgrade

“When I was pregnant,” Guardian columnist and feminist Zoe Williams recalled in 2010, “I managed to lose the dog's lead, between the common and the house. So I took my jumper off and tied him to that, only I forgot that I wasn't wearing a proper top underneath – I was wearing something in the region of a string vest. How could I not notice? Why was I even wearing a string vest?”.

Williams believes she was suffering from a kind of mental impairment brought on by the biological changes associated with pregnancy – an idea that’s been called variously preghead, pregnesia, momnesia and baby brain.

Surveys suggest that belief in pregnesia is widespread among the public. And given these views, perhaps it’s no wonder that researchers have uncovered disconcerting evidence about the prejudice shown towards pregnant women, especially in work contexts. In a 2007 study, participants role-playing as employers were less likely to choose a pregnant candidate than a non-pregnant rival with the exact same qualifications.

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The reality

The myth of pregnesia hasn’t come out of thin air. Countless surveys of pregnant women, using questionnaires and diary reports, have found that many of them – usually about two thirds – feel that being pregnant has affected their mental faculties, especially their memories.

But whilst subjective reports of this from pregnant women are widespread, objective laboratory studies are far less consistent. For many years, for every study that turned up an apparent impairment in memory, another was published that drew a blank.

An attempt to weigh all the evidence was published in 2007 when Julie Henry and Peter Rendell conducted a meta-analysis that gathered together all the evidence from 14 studies published over 17 years. Their conclusion? There is a real effect of pregnancy on women’s cognition, but it’s “relatively subtle”.

Unfortunately, Henry and Rendell’s abstract of their paper was worded in a way that proved ripe for misinterpretation. They wrote “The results indicate that pregnant women are significantly impaired on some, but not all, measures of memory”. By “significant” they meant statistically significant. But as Nicole Hurt details in her critique of the coverage (Legitimising “Baby Brain”: Tracing a Rhetoric of Significance Through Science and the Mass Media), journalists worldwide misunderstood the research summary and the public message became sensationalised: “many [pregnant] women … suffer considerable memory loss” (from The Observer; emphasis added) is just one example.

Since the meta-analysis, the literature has taken a number of further twists and turns. An Australian study published in 2010 was superior to many of its predecessors in following a large group of women before, during and after pregnancy. Helen Christensen and her colleagues found no evidence of pregnancy being associated with cognitive decline. In turn this spawned a whole new set of headlines around the world – “Pregnant women’s brains are not mush” the Daily Telegraph announced.

And yet the evidence supporting the idea of pregnancy-related effects on memory just keeps coming. Here’s a flavour of some recent findings: In 2011, Carrie Cuttler and her colleagues studied 61 pregnant women and found evidence of memory problems in real-life “field tests” of their prospective memory (remembering to do things in the future), but no evidence of memory problems in the lab. In 2012, Danielle Wilson and her team published a study that found evidence of memory impairment in pregnant women compared with non-pregnant controls. Crucially, this study involved sleep monitoring and the verbal memory impairment in the pregnant women wasn’t attributable to sleep disturbance.

Animal research and the maternal upgrade

The cognitive problems associated with human pregnancy are rather mysterious in light of research with rats and other mammals that suggests pregnant females undergo cognitive enhancements, not impairments, that stay with them into motherhood. A pioneer in this field is Craig Kinsley at the University of Richmond. He told The Psychologist magazine in 2010: “Our [maternal] rats get better at virtually everything they need to, to successfully care for their expensive genetic and metabolic investments. Foraging, predation, spatial memory all improve; stress and anxiety responsiveness decreases.”

When I asked Craig Kinsley why the human literature was full of findings about cognitive impairments whilst the animal research points to improvements, he said the disparity may have to do with the kinds of tasks and behaviours that were being studied in humans.

At last, a recent spate of studies may be hinting at maternal advantages in humans too. James Swain’s lab at the University of Michigan has shown how several areas in the brains of new mothers are especially responsive to the sound of their own baby crying, compared with the sound of other babies cries.

Regarding physical brain changes, a team led by Pilyoung Kim at Cornell University and Yale University School of Medicine scanned the brains of 19 new mothers in the weeks immediately after giving birth and then again several months later. The later scan showed up increased volume in a raft of brain areas that are likely to be involved in mothering activities – the prefrontal cortex, parietal lobes, hypothalamus, substantia nigra, and amygdala.

And in 2009 and 2012, labs at the University of Bristol and Stellenbosch University, respectively, reported evidence that pregnant women have a superior ability to determine whether a face is angry or fearful, and they show heightened attention to fearful faces. The Stellenbosch team wrote: “Heightened sensitivity to danger cues during pregnancy is consistent with a perspective that emphasizes the importance of parental precaution and the adaptive significance of responding to potentially hazardous stimuli during this period.”

More findings like these are bound to appear as researchers begin to test pregnant and recently-pregnant women on behaviours and mental activities that are directly relevant to raising a child. That pregnancy has a profound effect on the brain and mental function of women seems increasingly certain. But the idea that it’s a purely negative effect is a myth that's in the process of being debunked. Any pregnancy-related impairments are likely a side-effect of what ultimately is a maternal neuro-upgrade that boosts women's ability to care for their vulnerable off-spring. Many will welcome the demise of the pregnesia myth, because it's a simplistic, one-sided concept that almost certainly encourages prejudice against women.

Christian Jarrett, Ph.D is the editor of the British Psychological Society's Research Digest blog and staff writer on their magazine The Psychologist.

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