Wednesday, February 27, 2008

Good News for Ugly Babies

ResearchBlogging.org

Babies really have it made. They usually have at least one, and sometimes a coterie, of people in their life devoted to figuring out exactly what will make them happy, whether it be food, milk, a pacifier, etc. They also have the privilege of enjoying a warm, cooing welcome from almost anyone they encounter, be it a close relative or complete stranger. Not many of us have the ability to turn away from a smiling baby with cold indifference, and some will stop whatever they are doing just to walk over to tell the infant how cute he/she is.

Charles Darwin made the first scientific attempt at explaining the affinity most people have for babies. He suggested it involves an evolutionarily adaptive mechanism. Babies are the evolutionary goal of procreation realized. Considering the biological investment made in bearing a child, along with its individual helplessness, it would be adaptive for a species to be inclined to treat their young with a caring hand. Konrad Lorenz, a pioneer in explaining instinctive behavior, further elucidated on this idea, suggesting there are specific aspects of an infant’s facial features that automatically elicit a parental response, even from a non-parent.

Neuroimaging studies have indicated that parents do show increased activity in areas of the brain associated with rewarding events (nucleus accumbens, anterior cingulate, amygdala) when they see an infant’s face, even if it is not their own child. People who are already parents may be naturally more inclined toward positive feelings when seeing a baby’s face, however, as it could cause them to generate a pleasing comparison to their own child, or even just stem from their familiarity with infantile features. To determine if a predilection for infants is a universal trait, participants who aren’t parents would need to be included in such a study.

Recently, a group of researchers did just that, conducting a study that involved both parents and non-parents. They used magnetoencephalography, an imaging technique that measures magnetic fields produced by the brain’s electrical patterns (quite possibly the future of neuroimaging), to image brain activity while participants viewed unfamiliar adult and infant faces (interspersed with other symbols). The faces were closely matched in expression and attractiveness to prevent these characteristics from playing a confounding role in the study.

They found that when infant faces were viewed, before normal activity in the brain associated with seeing a human face occurred (in an area called the fusiform face area), there was a surge of activity in the medial orbitofrontal cortex. The medial orbitofrontal cortex has been implicated in a number of previous studies in the perception of rewarding stimuli. This activity occurred only when viewing infant faces, and had an extremely rapid onset—about 130 ms after seeing the face. The speed of the response indicates it was probably non-conscious.

This finding seems to add support to Darwin and Lorenz’s theories of an instinctual preference for the features of infants. The authors of the study note it also may have some clinical importance, specifically in cases of postnatal depression. One of the most troublesome symptoms of postnatal depression is the tendency a mother can acquire to be unresponsive to her child. This coldness sometimes makes a crying infant even more uneasy instead of being pacified when their mother approaches. Links between depression and the cingulate cortex have been suggested, and the cingulate cortex is strongly connected to the medial orbitofrontal cortex.

The researchers plan to do follow-up studies to investigate if differences in levels of parenting experience, gender, or specific infant features might affect this reaction. But the indication that the initial response seems to be non-conscious implies there may be a neural reward mechanism in place that is specific to seeing an infant. It is easy to understand why such a trait would be adaptive for a parent to have, as the more solicitous parents are toward their offspring the better their progeny’s chances of survival. It also makes sense that the trait would become widespread, as in tribal groups kin selection could play a large role in making infant survival important. Thus, it could have eventually become a response almost all people, parent and non-parent alike, shared. I suppose no one should be surprised that another concept espoused by Darwin may one day help us to better understand human nature.

Reference:

Kringelbach, M.L., Lehtonen, A., Squire, S., Harvey, A.G., Craske, M.G., Holliday, I.E., Green, A.L., Aziz, T.Z., Hansen, P.C., Cornelissen, P.L., Stein, A., Fitch, T. (2008). A Specific and Rapid Neural Signature for Parental Instinct. PLoS ONE, 3(2), e1664. DOI: 10.1371/journal.pone.0001664

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