It's widely believed that babies can learn to recognize the sound of their mother's voice, or familiar music, while they are still in the womb.
Is there any truth to this, or is it merely anecdotal? In a new study, Renata del Giudice of the University of Salzburg and her colleagues set out to investigate what unborn babies might be able to learn, and to measure the brain activity associated with any learning that might take place.
They recruited 10 pregnant women, all in the third trimester of pregnancy, and asked them to record a nursery rhyme then replay it to their unborn babies twice a day during the few weeks leading up to birth. Two weeks after the babies were born, the researchers played the recordings once again, together with recordings of unfamiliar rhymes read by their mothers, and of the same familiar and unfamiliar rhymes read by strangers.
Meanwhile, they recorded the babies' brain responses, using a specially developed electroencephalography (EEG) system, consisting of an elastic net fitted with 128 scalp electrodes, which was designed to minimize the infants' stress before and during the experiment. The researchers looked for the synchronization of certain brain wave patterns in the prefrontal, frontal, parietal and occipital regions, which indicates the recognition of emotionally relevant information.
At two weeks after birth, the sound of the mothers' voices produced a greater degree of synchrony in one of the brain waves, known as the delta wave, across these regions than did strangers' voices. This suggests the babies were able to detect their mothers' voices and focus their attention towards it.
The researchers also made video recordings to monitor the mothers' interactions with their babies, and measured breathing rate and various other indicators of infants' stress during the experiment. They found that the sound of the unfamiliar rhyme recorded by a stranger increased the level of stress in all the newborns, but that the familiar rhymes, sang by both their mothers and strangers, had a calming effect.
The results, presented at the 19th annual meeting of the Association for the Scientific Study of Consciousness in Paris, lend support to the view that babies can become familiar with voices and other sounds played repeatedly to them before birth, and that they can learn while still in the womb.
"Now we want to confirm and replicate these findings using a larger sample size and a control group," says del Giudice, "and we also want to try to relate the babies' EEG responses to the attachment style of the mother."