Learning in the Womb

Historically, researchers studied habituation to determine whether the fetus could learn. Habituation is a decrease in response to a stimulus after multiple presentations. For example, in 1925, a German researcher honked a car horn repeatedly and observed that the fetus jumped less and less with more and more repetitions.⁶ The earliest habituation responses have been demonstrated at 22-23 weeks gestation and seem to occur earlier in females than in males.⁷  In another real-world example of fetal habituation, researchers studied mothers who moved to the Osaka airport neighborhood before the last four months of their pregnancy and found that their babies did not wake up or show significant changes in brain activity as measured by an electroencephalogram (EEG ) when the researcher played a recorded aircraft noise at 80dB. In contrast, these babies woke up when they heard an unfamiliar music sequence at the same volume – 80dB.⁸ Also, babies with more prenatal exposure to airplane noise slept better than babies whose mothers had only lived in the area near the airport for a short time.⁹

Learning can also be documented from one prenatal age to another. Interestingly, non-startling sounds evoke mild heart-rate decelerations in the womb, whether the fetus is awake or asleep.¹⁰ In a clever study that uses this change in fetal heart rate, researchers asked mothers to read a nursery rhyme out loud starting at 28 weeks gestation or 32 weeks. They found that fetuses who started at 28 weeks took 5 weeks to learn the rhyme, as shown by a large heart-rate deceleration, but fetuses who started at 32 weeks learned the rhyme in just two weeks.¹¹ In a follow-up study, researchers asked women to recite a rhyme from 28 to 34 weeks. They assessed the fetus’s learning by recording heart rate decelerations and found that the fetus had usually become familiar with the rhyme by 34 weeks and that he remembered the rhyme at 38 weeks, even though he had not heard the rhyme in four weeks.¹²

In a more recent study, mothers listened to a descending piano melody twice a day from 35 to 37 weeks gestation. Then six weeks later, after their babies were born, the melody was played again while the babies quietly slept. All babies respond to music by slowing down their heart rate, but the babies who had heard the music before had a heart-rate deceleration that was twice as large as the babies who had never heard the music before.¹⁴ This was the first example of learning in utero that lasted many weeks after birth. Another group asked pregnant women to listen to a melody five times per week from 29 weeks until birth. When they studied brain activity in these infants, they found that both at birth, and at four months old, these infants responded to the familiar melody with greater brain activity than babies who had never been exposed to the melody.¹⁵ The more that the babies had heard the melody prenatally, the stronger their brain response.¹⁶ Other researchers have had difficulty seeing this long-lasting prenatal learning, perhaps because they used fewer prenatal exposures.¹⁷

Finally, the fetus also learns about tastes and smells. For example, if a mother eats garlic while she is pregnant, her newborn exhibits less aversion to garlic than newborns whose mothers did not eat garlic.²⁰ Similar results have been seen for anise and vanilla.²¹ Furthermore, when women frequently drank carrot juice during their third trimester, their babies showed less aversion to carrot-flavored cereal when they started eating solid foods six months later.²² This suggests that taste-learning lasts for months and may be more robust than auditory learning in the fetus.