Fascinating new research from University of Helsinki researchers shows that a fetus in utero can hear sounds outside the womb during the last trimester of pregnancy. These children were found to recognize, after birth, a word that had been repeated to them while in the womb. (So: Watch your mouth, think before you speak, etc.) Read on!

It may seem implausible that fetuses can listen to speech within the womb, but the sound-processing parts of their brain become active in the last trimester of pregnancy, and sound carries fairly well through the mother’s abdomen. “If you put your hand over your mouth and speak, that’s very similar to the situation the fetus is in,” says cognitive neuroscientist Eino Partanen of the University of Helsinki. “You can hear the rhythm of speech, rhythm of music, and so on.”

… Partanen and his team decided instead to outfit babies with EEG sensors to look for neural traces of memories from the womb. “Once we learn a sound, if it’s repeated to us often enough, we form a memory of it, which is activated when we hear the sound again,” he explains. This memory speeds up recognition of sounds in the learner’s native language and can be detected as a pattern of brain waves, even in a sleeping baby.

The team gave expectant women a recording to play several times a week during their last few months of pregnancy, which included a made-up word, “tatata,” repeated many times and interspersed with music. Sometimes the middle syllable was varied, with a different pitch or vowel sound. By the time the babies were born, they had heard the made-up word, on average, more than 25,000 times. And when they were tested after birth, these infants’ brains recognized the word and its variations, while infants in a control group did not, Partanen and colleagues report online today in the Proceedings of the National Academy of Sciences.

Babies who had heard the recordings showed the neural signal for recognizing vowel and pitch changes in the pseudoword, and the signal was strongest for the infants whose mothers played the recording most often. They were also better than the control babies at detecting other differences in the syllables, such as vowel length. “This leads us to believe that the fetus can learn much more detailed information than we previously thought,” Partanen says, and that the memory traces are detectable after birth.

Before you rush out for headphones wide enough to fit your expectant abdomen or decide whether your child should learn Spanish or Arabic first, keep in mind that it’s not clear that “stimulation beyond normal sounds of everyday life offers any long-term benefits to healthy babies.” These findings may, however, have implications for treating children “at risk for dyslexia or auditory processing disorders.”