Oct. 25, 2010 -- ''Mommy brain" -- used to describe that spacey, sleep-deprived state when new moms tend to forget things and act scatterbrained -- may not be the whole story on what happens to women's brains after giving birth.
''We observed increases in gray matter in many areas of the brain ... which play an important role for maternal motivation and reward processing," says Pilyoung Kim, PhD, a developmental psychologist and post-doctoral researcher at the National Institute of Mental Health, who did the research while at Yale University.
Her report is published in the journal Behavioral Neuroscience.
A Closer Look at 'Mommy Brain'
Kim and her colleagues did high-resolution magnetic resonance imaging (MRIs) on the brains of 19 women who delivered babies at Yale-New Haven Hospital.
The first scan was done two to four weeks after the women gave birth.
"We invited the same mothers back again after three or four months and scanned the brain structure again, and we observed the differences in brain matter volume," Kim tells WebMD.
The mothers also rated their babies and communicated their thoughts about parenting. They selected from a list of words that described their perceptions of their new babies or their experience as mothers. The baby words included such terms as beautiful, ideal, perfect, and special.
For parents, the word list included blessed, proud, content.
On the scans, the areas that changed included areas involved in maternal motivation, emotion and reward processing, sensory integration, reasoning, and judgment.
"We found growth in brain areas ... which may be responsible for interacting with your child, finding your baby to be special, planning and monitoring your parenting behavior, and engaging in warm parenting behavior," Kim tells WebMD.
Mothers who rated their babies most enthusiastically, rating them as special or perfect or in other positive ways, were likely to have more increases in the gray matter in the regions that had growth, she found.
What's happening? Kim says the study only shows a correlation between parenthood and brain changes, but speculates what could be happening. "The first few months [of motherhood] are especially stressful and intense," says Kim. "But at the same time the mothers' brains go through changes so the mothers can focus their energy on their own infant better, finding more positive meaning from their infant so they can develop emotional bondings with their infants."
True, Kim says, that many mothers report they cannot remember things well when they have newborns. But some research suggests that improves over time.
It's difficult to quantify the brain changes found on the scans, Kim tells WebMD. "I would say it's a small change, but a significant change."
More Input on Brain Growth After Giving Birth
The new research is ''beginning to translate animal work into meaningful human connections," says Craig H. Kinsley, PhD, professor of neuroscience at the University of Richmond in Virginia, who wrote a commentary accompanying the study and has also done work in the field.
The finding of brain growth is not surprising, he tells WebMD. ''The work that we have done and others have done indicates there are functional differences in the brains of mothers versus non-mothers and anatomical differences."
Recent research, Kinsley says, has prompted experts to rethink what some term the ''construction of the maternal brain." It may not be as instinctual as people believed, he says.
"When most people look at the interaction between a mother and her infant, most would assume it is unilateral. But in fact there are a tremendous number of stimuli coming back from that infant to the mother," he says.
"That stimulation doesn't just bounce off the brain, it causes the brain to respond in ways that you would expect based on what Kim showed."
It may be the combination of hormones and the flood of stimuli from the infant (when he's hungry, wet, distressed) that lead to brain changes and behavior changes, Kinsley says.
"Now you have this symbiosis if you will," he says.
In research looking at so-called ''pregnancy brain," he says, the vast majority of the work was focusing on verbal memory and cognitive skills. But having a good vocabulary and remembering numbers aren't behaviors crucial to bonding with a newborn, he says.
So far, the research by Kim's group shows correlation with birth and maternal brain changes, not cause-and-effect, Kinsley agrees. But, he adds, "If I had to guess, I'd guess it's related to hormonal changes in the mothers during pregnancy and value added from the infants once they arrive."
Both Kim and Kinsley say the research findings may eventually prove helpful in figuring out what might go awry in the brains of mothers who are indifferent or abusive.