It’s hard to resist flirting with babies. Even if a baby has been screaming her head off for hours on end in the seat behind you on a transatlantic flight, if she giggles and smiles when you’re deplaning, you’ll probably smile back. What is it about babies that makes our hearts melt almost instantaneously when we see them? Is it their cuteness, their happiness, or just their babyness?
A team led by Morten Kringelbach showed photos of babies and adults to twelve volunteers while their brains were being scanned with a MEG (magnetoencephalography) scanner. The key to the study was the control of the photos. Ninety-five judges had previously rated these pictures for the emotion they displayed and the attractiveness of the faces. Both the adult photos and the baby photos were rejected if they were rated as too attractive or unattractive: only middling pictures were chosen for use in the study. Each of the individuals — 13 adults and 13 babies — was depicted with a happy, sad, and neutral expression, and again all these photos were selected to have equivalent levels of emotional expression, so the viewers each saw 78 different pictures.
The MEG scanner, unlike fMRI, measures actual neuronal activity, and it responds extremely rapidly, allowing precise measurements within milliseconds after the cells in brain are activated. Viewers were told to look at a small red cross on the screen and press a button when it changed from red to green. They were told to ignore the pictures, which were flashed for about a third of a second between appearances of red/green cross. Of course the researchers were actually interested in the brain activity while the pictures were seen, and they ignored the data from when the cross actually changed color, which happened about 15 percent of the time. Here’s what they were really interested in:
The pictures show the difference in brain activation states at a given time compared to the 250 milliseconds before the pictures were viewed. As you can see, the pattern is different when viewers saw infant faces compared to adult faces. The most dramatic difference in brain activity occurred in the medial orbitofrontal cortex. This graph shows the dramatic difference in activity in that region when viewing baby faces compared to adult faces:
This area of the brain has been shown to be activated in a similar pattern when people see masked drawings — drawings that they don’t actually remember seeing because they are flashed so briefly. So almost immediately after seeing infant faces, adults show a dramatically different response compared to equivalently emotional and attractive adult faces; a response they may not even be aware of.
Kringelbach’s team speculates that their research might be applicable in treating postpartum depression, where mothers seem emotionally unaffected by their new babies. It’s possible, they say, that this area of the brain responds differently in mothers suffering from postpartum depression.
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