The brain circuitry needed to learn language is in place at birth, but the "wiring" hasn't been hooked up yet. For that to happen, neurons must fire over and over again to strengthen connections called synapses. This is where parents and caretakers play a crucial role: Some scientists speculate that what detonates these charges is repeated auditory, verbal, and sensory experience. You say your baby's name, and your baby hears you. Zap. You smile at your baby, and your baby smiles back. Zap. Do this a thousand times, and with each repetition the faint threads of new connections are fortified in your infant's brain until they're like steel cable. Synapses multiply steadily between 9 months and 2 years old. Then, once the developmental synapses required for early language learning are no longer needed, huge numbers of them wither away.
To compensate for the fact that their linguistic circuits aren't in full working order for at least a year, babies have certain perceptual abilities that help them recognize elements of language -- even before they're born. Peter Jusczyk, a professor of psychology and cognitive science at Johns Hopkins University in Baltimore and author of The Discovery of Spoken Language, says that babies' exposure to speech while in the womb actually affects how they react to language after they're born. "We know that infants are sensitive to rhythms and that newborns can differentiate between the mother's language and a foreign language," he says. What they're picking up on is the musicality of the language they've grown accustomed to hearing during their nine-month gestation. "If you listen to a person talking through a wall, what you hear are rhythms and intonation patterns. That's what comes through in the womb," Jusczyk says.
Along with French colleague Jacques Mehler, Jusczyk played tapes of French and Russian to 4-day-old French babies. In order to hear the voices, the newborns had to suck on their pacifiers. When the voice was in their native language, they sucked harder; when it wasn't, they sucked less. Even when the words were electronically filtered to muffle pronunciation, the infants were still more interested in the melody of their mother tongue.