Pregnancy brain typically refers to lapses in attention and memory. About 80 percent of new mothers report difficulties remembering things that once came naturally, and although not all studies support this, the weight of the evidence shows that during pregnancy, women exhibit measurable declines in important cognitive skills.

But it's not all bad news. The maternal brain also features important enhancements. Mother rats score higher in tests of attention, foraging and planning than peers who have never given birth. These gains most likely render them better able to defend and provide for their pups.

The benefits for human moms are less clear, but data are emerging that suggest human pregnancies initiate neural restructuring. A 2010 study found that in the first few months after giving birth, human females show changes in several key brain regions. Specifically, they often exhibit increased volume in the hypothalamus, striatum and amygdala—areas essential for emotional regulation and parental motivation—as well as in regions governing decision making and protective instincts.

We can glean further evidence from behavioral changes during pregnancy. Many women exhibit blunted physiological and psychological responses to stress, which may afford mother and fetus protection from the potentially adverse effects of taxing situations. And in the postpartum period, the hormones that sustain breast-feeding maintain these dampened stress responses.

Pregnant women are also better at recognizing fear, anger and disgust. This enhanced ability to identify and discriminate among emotions may help mothers to ensure their infants' survival. Research from my laboratory has shown that the hormone exposures in pregnancy—for example, high levels of estrogens and oxytocin—are associated with heightened maternal responsiveness and sensitivity to the environment and infants' needs.

Pregnancy primes the brain for dramatic neuroplasticity, which is further stimulated by delivery, lactation and mother-child interactions. Some evolutionary biologists have argued that the development of maternal behaviors is the primary force shaping the evolution of the mammalian brain. Of interest, these alterations may become more pronounced with each successive pregnancy and persist throughout a mother's life span. But helpful adaptations are rarely achieved without an associated cost—and pregnancy brain may reflect just such a cost.

Although our understanding is still in its nascency, it is clear that pregnancy marks the start of a critical period of neurodevelopment for women. This period prepares mothers for the myriad challenges of providing for a vulnerable infant.

Question submitted by Chelsea Brennan DesAutels, Minneapolis


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