7/19/12 - a mother's brain changes with the birth of a child

In today's encore excerpt - a new and growing body of research is revealing that there are marked and generally positive physiological changes that occur in a mother's brain as a result of giving birth to a child. Experiments and observations on human mothers and laboratory rats provide the evidence:

"Research suggests that motherhood enhances certain types of cognition, improves resistance to stress and sharpens some kinds of memory. On the face of it, the fact that the nervous system manages to transform a new mother from a self-centered organism into an other-focused caregiver is actually quite impressive. All it takes is for new neurons to sprout, certain brain structures to blossom in size and waves of powerful hormones to batter the pregnant woman's physiology. The result is a different and in some ways better brain -- or at least one capable of juggling the challenges of everyday life while maintaining a laserlike focus on the baby.

"Of all the senses, smell -- olfaction -- plays the largest role in reproduction. Females rely on their sense of smell from the very beginning to help them select their mates all the way through to the weaning of their young, during which scents act as a form of communication between mother and child. An extreme example of the power of smell is known as the Bruce effect, a phenomenon in which certain scents induce abortions in pregnant rodents. If a female's mate disappears after conception and an interloper starts hanging around, the new male's smell will inhibit the production of key hormones, causing the female's pregnancy to abort. Otherwise, chances are high that the interloper would end up killing and eating the pups, thereby obtaining a high-protein meal and removing a rival's genes in the bargain. ...

"During a rat's pregnancy, for example, we know that the olfactory system starts churning out new neurons. The theory is that the extra neurons allow moms to become more adept at processing the cues hidden in infant odors. Indeed, mothers distinguish themselves quite obviously in how they react to smells. Whereas virgin female rats find the odors of infants noisome, once they become pregnant, those smells attract them. ...

"Mother rats seem to excel at tasks that require enhanced attention. Behavioral neuroscientist Kelly Lambert of Randolph-Macon College and her colleagues have collected other evidence of sharp-witted mothers. In 2009 they showed that when it comes to identifying which cue among several signals food, mother rats perform best. And recent work by Amy Au and Tommy Bilinski in our lab has begun to identify the rats' strengthened ability to deduce the meanings of symbols. The researchers designed experiments where a rat in an environment learns to associate, say, a triangle or a set of wavy lines with a food reward. After being moved to a new environment, lactating females transferred their knowledge from the old setting to the new one better than virgin females did, again suggesting a heightened attention to detail.

"A human mother's brain undergoes a striking structural metamorphosis, too. Last year using magnetic resonance imaging studies, neuroscientist Pilyoung Kim, now at the National Institute of Mental Health, and her colleagues found significant increases in gray matter in mothers' brains in the weeks and months after they give birth. Gray matter, which got its name from the color of cell bodies, is a layer of tissue packed with neurons. The growth the scientists saw was particularly visible in the midbrain, parietal lobes and prefrontal cortex -- all areas involved in infant care. The mothers with the biggest increase in gray matter volume also reported the more positive perception of their babies.

"As the time of delivery nears, powerful hormones swing into action. Although the most obvious players are oxytocin, which stimulates uterine contractions and milk letdown, and prolactin, which instigates milk production, other hormones trigger changes inside the brain, too. ... Meanwhile the hypothalamus ramps up the feelings of pleasure a mother receives. Robert S. Bridges of the Tufts Cummings School of Veterinary Medicine and his colleagues found different concentrations of opioid receptors in female rats depending on whether the rodent was a virgin, pregnant or lactating. ... The drug analogy, by the way, is not spurious. Animals may in fact be engaging in maternal behavior simply because it feels good. Many human mothers report a very pleasurable feeling as they breastfeed their infants. After pups attach to a female rat's nipple, the mom receives a 'hit' of reinforcing opiate."


Craig Howard Kinsley and Elizabeth Meyer


"Maternal Mentality"


Scientific American Mind


July/August 2011


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