American researchers are a step closer to unravelling the mystery of how babies learn how to speak.
Scientists at the University of Washington in Seattle had a group of seven- and 11-month-old infants listen to a series of syllables while sitting in a brain scanner. Not only did the auditory areas of their brains light up as expected but so did a region crucial to forming higher-level speech, called Broca's area.
These findings suggest that even before babies utter their first words, they may be mentally exercising the pivotal parts of their brains in preparation.
Study author and neuroscientist Patricia Kuhl says her results reinforce the belief that talking and reading to babies from birth is beneficial for their language development, along with exaggerated speech and mouth movements.
"Understand that they want to talk with you - serve and volley - so give them a chance to talk back," she said.
Kuhl and her colleagues also threw a non-native language into the mix to see how babies' perception of speech sounds change as they grow. They looked at brain activation of the infants, all from English-only-speaking homes, while listening to a series of Spanish syllables.
As expected, a seven-month-old's brain reacted the same way when hearing both English and Spanish.
"That's why I call them citizens of the world," Kuhl said. "Then by 11 to 12 months they have become more like adults in their perceptions."
Adults have trouble distinguishing sounds that they did not grow up hearing or speaking, which is one reason learning a new language is so difficult.
The older infants studied were more stimulated by their native language for the auditory regions of the brain - kind of like perking up your ears when you hear your name in a noisy crowd. At only 11 months, the babies developed this kind of activation pattern seen in adults.
"Between six and 12 months, infants get better at telling apart the sounds their language uses, and worse at telling apart the sounds their language doesn't use," said psychologist Daniel Swingley, of the University of Pennsylvania.
The increase in language precision that occurs during the first year of life also means that older babies cannot distinguish those foreign sounds as well any more. They are now native speakers, to whom non-native languages now seem a bit odd.
"They lose the ability because they don't get exposed to those differences, so they unlearn them," said psychologist Richard Aslin, of the University of Rochester, who was not involved in the study. "The process of learning is really unlearning."
Using a technique called magnetoencephalography, or MEG, Kuhl and her colleagues were able to measure tiny magnetic fields generated by the firing of neurons in each baby's brain. In a second experiment with MEG, she used Finnish-learning infants with Putonghua as the non-native language.
Her results were similar to the English-Spanish study.
A person with damage to Broca's area can still comprehend language but typically talks very slowly and uses short phrases.
It is named after French surgeon Pierre Paul Broca.