‘Momnesia’? No, Pregnancy May Boost Intelligence

Research suggests that mental changes last well past delivery



See the column on the Wall Street Journal site


As a mother of three, I had always thought of pregnancy as a time of increased girth but decreased smarts. I wasn’t alone in thinking that my mental capacities were temporarily making way for the needs of the new arrival. Mommy Brain and Momnesia—pop terms for the sleepiness of pregnancy and the postpartum period—have branded such folk wisdom with the veneer of truth.

But that’s where the proof for Mommy Brain ends. Though many women say pregnancy makes their thinking fuzzy, an impressive body of research shows the opposite. Pregnancy and motherhood seem to make mothers smarter.

A 2014 study led by the late Craig Kinsley of the University of Richmond and published in the journal Hormones and Behavior showed that lactating mother rats beat childless rats at hunting—an asset not linked to any detectable uptick in their ability to hear, see or smell. Instead, mother rats had a fertility-related boost in mental power making them better at providing for themselves and their young.

Thanks to work by Dr. Kinsley and his team, we also know that the pregnancy-related hormones of motherhood restructure some brain areas not typically linked to reproduction, such as the hippocampus. This seahorse-shaped brain area consolidates memories and helps us figure out how to navigate through space. Motherhood-related hormones might explain why pregnant and lactating rats beat their non-reproducing female peers at running mazes, for example.

Amazingly, these hormones can also protect mothers’ brains from injury, says Adam Franssen, an associate professor of biology at Longwood University in Virginia and a former colleague of Dr. Kinsley’s. Five years ago, Dr. Franssen led a study that exposed mother rats and childless rats to new experiences and then injected an acid into the rats’ hippocampi to create amnesia. The mother rats’ memory and problem-solving abilities rebounded more quickly, compared with female rats without offspring.

Recent evidence suggests that pregnancy induces changes in the human brain, too. In a study published a few months ago in the journal Nature Neuroscience, Elseline Hoekzema of Leiden University in the Netherlands and colleagues scanned the brains of about 80 women and men, half of them hoping to become parents. The couples who wanted to have a baby were scanned before pregnancy, then again if they got pregnant, after the baby was born and when the baby turned 2.

Women who became pregnant between the scanning sessions showed neural changes so distinct that a computer could distinguish between pregnant and nonpregnant women based on their brain scans alone. The heightened estrogen and progesterone hormones of pregnancy trimmed back some “gray matter”—the cell branches that connect neurons to each other-—which has the effect of sharpening, not diminishing, mental capacities. The neural pathways that remain are streamlined and strengthened in the process.

“An analogy would be moving to a neighborhood and trying to find the best way home from work. Each day you take different routes, eventually settling on the most efficient route. You’ve pruned out the less efficient neural pathways and can travel the main route with almost no effort. The same is likely true during pregnancy and birth. The hormones of pregnancy help the brain refocus on the new priority in the mother’s life,” Dr. Franssen says.

The regions affected included ones linked to maternal bonding and memory. And the changes weren’t temporary. As Dr. Hoekzema said in an interview, they lasted for at least two years after a child was born.

Cognitive tests showed that this pruning of gray matter was associated with greater social acuity, and there was no attendant decline in the women’s intelligence. The mothers’ neural pruning affected the same areas that were activated—brain regions linked to empathy and nurturing—when they saw photos of their own babies. The change is “really about refinement and specialization…and a better recognition of emotions,” Dr. Hoekzema told me.

Add these findings to a big Swedish study released in March, showing that parenthood is linked to living longer in both sexes, and we can discredit two old saws: Children do not take years off your life, and pregnancy does not erode your smarts.