Cover Story
Kyra DeBlaker-Gebhard is normally an ace at keeping track of special occasions. But since she's been pregnant, "I can't remember a birthday, a graduation or an anniversary," laments the 30-year-old Washington, D.C., writer.
Her communication skills have also taken a plunge: "Especially in my first trimester, I had a very difficult time speaking coherently and writing clearly," she says.
DeBlaker-Gebhard is far from alone: Between 50 percent and 80 percent of pregnant women report memory and thinking problems during this time.
"Until I finally talked to a friend about it, I thought it was just me," DeBlaker-Gebhard says.
Recently, researchers have been examining whether this phenomenon--dubbed "baby brain"--has an objective basis. It's part of a recent wave of research looking at how pregnancy and motherhood affect women cognitively, a different slant from previous research that has focused on brain areas and processes that more directly influence females' propensity to nurture their young.
The findings suggest an intriguing picture that is good news for anyone embarking on the adventure of motherhood, notes University of Richmond neuroscientist Craig Kinsley, PhD, a main researcher in the area. Pregnant women do in fact experience a physiologically based baby brain, the likely result of a hormone flood that peaks in the third trimester as well as possible external factors, such as a more chaotic life during pregnancy, studies are showing. But related research finds that once the women give birth, other brain mechanisms kick in that help them protect their young by bolstering their cognitive abilities, and these benefits may last into old age.
"There is a tendency to see pregnancy and lactation as somewhat debilitating conditions," says Kinsley. "However, when it comes to motherhood, we're looking at changes that are beneficial to the female, and for the majority of her life."
Support for 'baby brain'
In the most stark evidence that the baby brain phenomenon is real, research has found that the brain actually shrinks a little during pregnancy. In a study reported in the January 2002 American Journal of Neuroradiology, Angela Oatridge, PhD, of Hammersmith Hospital in London, and colleagues found that women's brain volume diminished by about 4 percent during pregnancy, then returned to normal after delivery. Similarly, a study reported in the February 2000 Hormones and Behavior (Vol. 37, No. 1) by neuroscientist Liisa Galea, PhD, of the University of British Columbia, found that the volume of the hippocampus-a key center for memory and spatial learning--was smaller in pregnant rats than in nonpregnant rats.
In other studies, Galea showed that rats in their third week of pregnancy-the equivalent of the first human trimester, when levels of progesterone, estradiol, prolactin and related hormones are at their peak-showed decreased spatial learning ability compared with nonpregnant rats, an effect others have found during the early postpartum period as well.
Galea also has been studying new nerve growth in the hippocampus, both in pregnant rats and in rat mothers, known as dams. It's an intriguing area of study, she says, because the hippocampus is noted for its ability to generate new nerve cells throughout adulthood. Interestingly, she found no differences in nerve-cell growth in pregnant rats compared with virgin rats, and much lower levels in rat dams during the early postpartum period.
The findings suggest that on the biological level, pregnancy and the early postpartum period "are almost like a down time," Galea says. "Given that hormone levels rise to at least 1,000 times their normal levels during the third trimester, then plunge around birth, it's not surprising that some things get muddled in that hormonal soup."
In humans, it is difficult to study such brain and nerve-cell changes. As a result, researchers who study pregnant women generally focus on the women's performance on cognitive and memory tasks-important, they say because people are often notoriously inaccurate when it comes to assessing their memory abilities. So far, they've found that just as in rats, pregnant women perform worse on some learning and memory tasks than nonpregnant controls.
For example, in a meta-analysis of studies on pregnant women and memory functioning reported in the November 2007 Journal of Clinical and Experimental Neuropsychology (Vol. 29, No. 8), psychologists Julie Henry, PhD, of the University of New South Wales, and Peter G. Rendell, PhD, of Australian Catholic University, found a pattern: Pregnant women across all trimesters performed slightly worse than matched nonpregnant controls on memory tasks that impose particular demands on executive functioning, which encompasses higher-level thinking processes for creating and actualizing goals. Those effects lasted up to a year postpartum, they found.
In another study, the team examined how pregnancy affects prospective memory-our ability to remember to perform intended future actions, such as taking medicine at a particular time-known to be highly sensitive to failures in executive control. Pregnancy researchers are particularly interested in studying prospective memory because it is susceptible to real-life distractions, to which pregnant women and new mothers are especially vulnerable to, the researchers note.
In the study, published online March 14 and now in press at the Journal of Clinical and Experimental Neuropsychology, Rendell and Henry compared women in their third trimesters with controls on two types of prospective memory tasks, one in the lab and one in the field. The tasks were similar in that each combined aspects of real-life functioning and a lab-test paradigm. The lab test was a board game called "Virtual Life," which required participants to make choices about daily activities and remember to carry out lifelike tasks, while the field task required women to remember from home to push a button and log in the time at prescribed times over seven days.
Although the two groups performed equally well on the lab tests, pregnant women did significantly worse than controls on remembering to follow through on the field task.
In a related, as-yet-unpublished study, University of British Columbia doctoral student Carrie Cuttler, UBC Psychology Professor Peter Graf, Galea and UBC postdoctoral fellow Jodi Pawluski, PhD, compared 61 women in all three trimesters of pregnancy and 24 nonpregnant controls on lab and field measures of prospective memory. Again, the women did equally well on the lab tests, but women in the first trimester did significantly worse than others on the field-based prospective memory task.
Though it's unclear why the two studies found differences in the stage at which women were most affected, both suggest that lifestyle factors may be exacerbating a subtle underlying deficit, the researchers agree.
"We have a hard time finding these problems when pregnant women are in a distraction-free, sterile lab environment," says Cuttler. "But when women are in their everyday lives and they're dealing with all of these competing demands--their husbands and children pulling them this way, their work pulling them another way--that's when you see these deficits."
Findings on older adults underscore the point, notes Rendell. In other studies, he has found that older adults-who often have more structured, familiar routines compared to younger adults-tend to perform well on real-life prospective-memory tasks, but worse on lab tests.
"These differences suggest that lifestyle is working to support older adults and challenge the pregnant women," he says.
Motherhood as the fix?
After delivery, though, these deficits appear to reverse, at least in animals. In a paper in the February Archives of Sexual Behavior, (Vol. 37, No. 1), the University of Richmond's Kinsley summarizes a decade of work that he, his students and others have done showing that mother rats, monkeys and even beetles perform better on learning, memory and cognition tasks than nonmothers. His lab also has found brain and nerve-growth correlates for some of these phenomena. (Kinsley was the first to show that motherhood enhances spatial learning and memory in rat dams.)
Over time, Kinsley and others have tested two evolution-based hypotheses on why mothers may develop new cognitive and memory skills. One is that their brains and hormones change to enhance their abilities to fend off predators, leave the nest to find food and return quickly so their young aren't attacked. The other theory is that these changes reduce the mothers' fear and anxiety so they can better face such challenges.
"We and other labs have found a lot of support for both," Kinsley says. As a recent example bolstering the first hypothesis, an unpublished study by Kinsley's students Naomi Hester, Nathalie Karp and Angela Orthmeyer found that over three trials, mother rats were five times faster than virgin rats at catching crickets. Meanwhile, researchers including Inga Neumann, PhD, of the University of Regensburg in Germany have shown that pregnant and lactating rats are less prone to fear and anxiety in the face of stress than virgin rats, as measured by fewer stress hormones in the blood.
Kinsley's team is now looking into other ways animals' physiology may change to accommodate motherhood, such as improved blood flow and motor skills. Like Galea, Kinsley has also looked at nerve growth in the hippocampus of pregnant, mother and virgin rats. He found an increase in dendritic spines on neurons in an area that regulates some types of learning in pregnant and mother rats compared with virgin rats, he says.
Pawluski and Galea are seeing a more mixed picture. They find decreased dendritic branching in the hippocampus in first-time dams at the time of weaning and more dendritic spines in second-time moms. But on behavioral measures, rat moms perform significantly better on spatial working memory tests than nonpregnant rats, with first-time moms performing the best of all.
One potential explanation for those contradictory findings is that the enhanced learning in first-time dams may be partially caused by stress hormones, which tend to be higher in pregnancy and especially in first-time mothers. In addition, the team has not yet looked at nerve-cell growth in dams that have had more than one pup, Galea says. It is also possible that the "nerve pruning" that takes place during motherhood actually benefits spatial learning, she speculates.
Later rewards
Meanwhile, Kinsley's lab is also looking at the brains of rat moms that are past bearing age to see if earlier benefits accrue into older age. In a study headed by Kinsley's student Jessica D. Gatewood, reported in the July 2005 Brain Research Bulletin (Vol. 66, No. 2), the team found that at 24 months-the equivalent of a person's mid-80s-mother rats were better at learning spatial tasks and showed less memory decline than age-matched rats that were never pregnant.
In examining the older dams' brains on autopsy, the team also found significantly reduced levels of immunoreactive amyloid precursor protein, a marker of neurodegeneration and age-related cognitive decline, including Alzheimer's disease, Kinsley says.
For him, such changes suggest a place for motherhood alongside other natural developmental periods such as sexual differentiation, puberty and menopause.
"This is another epoch in a female's life," he says. "The brain changes are as dramatic as what you see during the other phases."
Tori DeAngelis is a writer in Syracuse, N.Y.
