Babies start with simple vowel sounds — ooh's and aah's. A mere months later, the cooing turns into babbling — "bababa" — showing off a newfound grasp of consonants.

A new study has found that a key part of the brain involved in forming speech is firing away in babies as they listen to voices around them. This may represent a sort of mental rehearsal leading up to the true milestone that occurs after only a year of life: baby's first words.

Any parent knows how fast babies learn how to comprehend and use language. The skill develops so rapidly and seemingly without much effort, but how do they do it?

Researchers at the University of Washington are a step closer to unraveling the mystery of how babies learn how to speak. They had a group of 7- 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 may 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 that 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 ("Hiii cuuutie! How are youuuuu?").

"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 7-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."

Listen to what the babies heard in English:

And here's what they heard in Spanish:

Adults have trouble distinguishing sounds that they didn't grow up hearing or speaking, which is one reason why learning a new language is so difficult.

"When you take French class in high school and you can't tell apart 'blanc' and 'blond,' that's because you didn't learn those vowels when you were a child," psychologist Daniel Swingley, of the University of Pennsylvania, wrote in an email. "But you can tell 'sheep' from 'ship,' which your Parisian counterparts have the same problem with," said Swingley, who was not involved with the study.

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 6 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," Swingley said.

The increase in language precision that occurs during the first year of life also means that older babies can't distinguish those foreign sounds as well anymore. 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."

Here’s a video of one the babies in the experiment:

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. Because the signals are so faint, the MEG machine uses liquid-helium-cooled superconducting sensors and requires extensive shielding from any outside magnetic activity, including the Earth's magnetic field.

"It looks like a hair dryer from Mars," Kuhl said of the multimillion-dollar system.

In a second experiment with MEG, she used Finnish-learning infants with Mandarin Chinese as the non-native language. Her results were similar to the English-Spanish study.

The engagement of Broca's area at such an early age is intriguing to Aslin, since it has been known to play a role in the motor coordination of speech in adults.

An individual with damage to Broca's area through stroke or tumor can still comprehend language but typically talk very slowly and use short phrases. It is named after French surgeon Pierre Paul Broca, who in 1861 described a 51-year-old patient of his who could only utter a single word: tan. He became known by the name Tan throughout the hospital, and after he died, an autopsy revealed a lesion on his left frontal lobe — now known as Broca's area.

But no piece of the brain is an island, and Aslin notes that sensory areas of the brain can be entwined. For instance, previous studies have shown that what we hear can be influenced by what we are looking at.

"I'm sure there's going to be some subtleties here about how these motor areas are actually connected with perceptual parts of the brain," he said.

Meeri Kim is a freelance science journalist based in Philadelphia.