The study, published in the current issue of NeuroImage, explored what happens in the brain when mothers are shown pictures of their babies, as well as images of unfamiliar infants. While all the photos increased the amount of activity in a part of the brain associated with emotion, the images of the mothers' own infants generally increased activity even more, suggesting that this brain region may be involved in maternal attachment.
Motivations for the study originated from a lack of reliable knowledge about positive emotions, says Jack Nitschke, a neuroscientist and assistant professor of psychiatry and psychology at UW-Madison. "We know that depression and anxiety are not accompanied solely by an increase in negative emotions, but also by a decrease in positive ones," says Nitschke, lead author of the paper. "Yet we know much more about negative emotions than about positive emotions."
Earlier studies have examined the effects of certain positive experiences on brain activity. But Nitschke notes that many of them are limited either in the scope of emotions elicited or in the reliability of the stimuli such as pictures, tastes or sounds to produce a positive emotional response. For example, while a picture of an ice cream cone may be pleasing to many people, those who are dieting or have an eating disorder may respond less favorably, says the Wisconsin neuroscientist.
To improve and expand upon previous studies, Nitschke and his colleagues wanted to use stimuli that evoke powerful feelings of positive emotion, such as warmth, joy and fulfillment.
"There's one stimulus that's universally positive: baby faces," says Nitschke. "Just looking at them gets most people, particularly new moms, feeling all warm and happy."
Testing the relationship between babies and positive emotion, the researchers invited six mothers and their infants to the laboratory. The researchers snapped up to 150 pictures of each baby, between the ages of 3 to 5 months. About six weeks later, the mothers, none of whom suffered from postpartum depression, returned to the lab.
This time, the mothers were shown photos of the happy faces of their babies, other people's babies, adult acquaintances and adult strangers. The women looked at these photos during a series of brain scans. The scans, or functional magnetic resonance images (fMRI), captured activity in the mothers' brains.
While in the scanners, the mothers also rated their moods on a nine-point scale based on five feelings: happy, warm, loving, motherly and excited.
The mothers, when seeing pictures of their own babies compared to seeing someone else's baby or no image at all, showed greater activity in the orbitofrontal cortex - a brain region in the lower part of the frontal lobe that's involved in decoding the emotional value of a stimulus, such as whether it is a form of reward or punishment. The activity in this brain region was equally strong in both hemispheres.
One of the more interesting findings, notes Nitschke, is that the mothers' mood ratings corresponded to changes in the brain. For example, the more a mom said she was happy, the more activity there was in both orbitofrontal areas.
This relationship between mood and brain activity, Nitschke says, not only confirms that the orbitofrontal cortex is involved in emotion processing, but also suggests that it may play a role in maternal attachment, the unique bond between a mother and her child.
"Because positive emotion is an aspect of maternal attachment, this brain region is probably important for a mother's bond with her infant," says Nitschke. "There may be less brain activity there in a mother with postpartum depression."
The UW-Madison researchers plan to explore the possible connection between orbitofrontal cortex activity and postpartum depression in a follow-up study similar to the one just published. That study will include new mothers who are diagnosed with this condition, which can leave them feeling sad, depressed, anxious and irritable months after childbirth. The researchers also plan to image the brains of new fathers as they look through a series of baby photos.
Overall, Nitschke says, "This study provides further evidence for the sage saying to stop and enjoy the little pleasant things in life, such as looking at pictures of your child or even receiving small rewards for doing something well - both of which involve activation of the orbitofrontal cortex. This puts you in a better mood and leads to brain changes that correspond to feeling happier."
- Emily Carlson 608-262-9772, firstname.lastname@example.org
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