http://www.nature.com/nsu/040126/040126-3.html#
(Click on the link to take the simple test to find out which side of your
brain processes emotions.)

Do women clasp infants to their left to boost bonding?
Cuddling linked to how the brain processes emotion.
28 January 2004
HELEN R. PILCHER

Women are more likely to cradle babies on their left-hand side because it
activates bonding-related brain regions, research suggests.

Previous studies have shown that up to 85% of women instinctively clasp
infants to their left breast - irrespective of age and maternal status. Some
think mothers do this to keep the baby's head close to their hearts,
naturally soothing the child. Others rationalize the bias in terms of
handedness. Left-handed women say they prefer to hold their infant in their
stronger left arm. Right-handers argue it keeps their dominant hand free to
attend to the child.

But neither argument fully explains the phenomenon, argue Victoria Bourne
and Brenda Todd from the University of Sussex. Instead, it may come down to
differences in the brain.

The right side of the brain controls the left side of the body and usually
helps to process emotions, explains Bourne. So holding the baby on the
left-hand side may help to direct the sight of emotionally charged
information, such as tears or laughter, to the specialized right hemisphere
for processing, she says.

To find out, the team asked 20 right-handed women to cradle a life-like
doll. As expected, over half of the ladies held the doll on their left side.
The team then found that these same subjects also use the right side or
hemisphere of their brain to process the image of a face laden with
emotion1.

"It may help the woman monitor the baby for signs of discomfort, pain or
hunger," says Bourne. And, she adds, this may boost mother-infant bonding.

Lateral thinking

But not everyone uses the right side of their brain to process emotional
faces. Some use the left-hand side, and others use a bit of both.

The team assessed which side of the brain their subjects used to process
emotions by asking them to identify which of two images looked happiest
(take the test). The pictures were mirror-image faces, each split vertically
down the middle, with one half smiling and the other wearing a neutral
expression. People who use the right side of the brain to process emotion
find the face smiling on the left-hand side the happiest, and vice versa,
explains Bourne.

It's a good task for assessing brain laterality, says Kim Bard from the
University of Portsmouth, who studies differences in brain hemispheres.
Brain scans can also be used, she says, but these can be time-consuming and
expensive, and miss out certain subtle differences.

All of the women in the test who cradled the doll on their left-hand side
used their right brain to process faces, the team found. Women who preferred
to cradle the doll on their right-hand side were just as likely to use their
left brain, right brain, or a mixture of both to process faces.

The result may carry a lesson for new mothers. Women with postnatal
depression are often advised to hold their baby on the left-hand side, says
Bourne, as this increases bonding for most women. But if the mother actually
uses the left side of her brain to process faces, this may not help, she
says.

References
Bourne, V. J. & Todd, B. K. When left means right: an explanation of the
left cradling bias in terms of right hemisphere specializations.
Developmental Science, 7, 19 - 24, doi:10.1111/j.1467-7687.2004.00318.x
(2004).

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