What can a fetus remember?
While no one remembers their experiences in the womb, the fetus can form memories that last for weeks.
For example, newborns remember sounds and tastes they experienced in the womb. Two- and three-day-old babies preferred to hear a story read to them twice a day by their mother in the six weeks before birth.
Newborns of this age also preferred a familiar lullaby sung by their mother during pregnancy compared to a new lullaby.
Newborns also preferred classical or jazz music when their mother had listened to either piece twice a day in the six weeks before birth.
Interestingly, this preference was observed when the music was played at week 36 of pregnancy, but not at week 30, suggesting that learning familiar sounds occurs after 30 weeks.
Habituation
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 repeatedly honked a car horn and observed that the fetus became less startled with increasing repetitions.
The earliest habituation responses have been demonstrated at 22–23 weeks of gestation and appear to occur earlier in women than in men.
In another real-world example of fetal habituation, researchers studied mothers who moved to Osaka’s airport district 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 electroencephalogram (EEG), when the researcher played a recorded airplane sound at 80 dB. In contrast, these babies woke up when they heard an unfamiliar musical sequence at the same volume—80 dB.
8 In addition, babies who were exposed to more aircraft noise before birth slept better than babies of mothers who lived near the airport for only a short time
Recognition
Learning can also be documented from one prenatal age to the next. Interestingly, non-startling sounds elicit mild heart rate decelerations in the womb, whether the fetus is awake or asleep.
10 In one clever study exploiting this change in fetal heart rate, researchers asked mothers to read a nursery rhyme aloud at either 28 or 32 weeks of pregnancy. They found that fetuses starting at 28 weeks took 5 weeks to learn the rhyme, as indicated by a large heart rate deceleration, but fetuses starting at 32 weeks learned the rhyme in only two weeks.
11 In a follow-up study, researchers asked women to recite a rhyme between 28 and 34 weeks. They assessed the fetus’ learning process by recording heart rate decelerations and found that the fetus usually knew the rhyme by 34 weeks and remembered the rhyme by 38 weeks, even though it had not heard the rhyme for four weeks.
How does transnatal learning help the newborn?
New evidence suggests that newborns can learn speech sounds from their native language in the womb
. A group of researchers gave pregnant women a recording of made-up words like “tatata” and “tatota,” interspersed with music, to play five to seven times a week from 29 weeks until birth. By the time the babies were born, they had heard the made-up words more than 25,000 times. Amazingly, when these babies were tested after birth, their brains showed the neural signals for recognizing vowel changes mid-word. The signal was strongest in babies whose mothers had played the recording the most times.
These results provide compelling evidence that language acquisition begins in the womb.
Can the fetus remember tastes and smells?
Finally, the fetus also learns about tastes and smells. For example, if a mother eats garlic during pregnancy, her newborn shows less aversion to garlic than newborns whose mothers did not eat garlic.
Similar results have been observed for anise and vanilla.
Furthermore, babies born to women who regularly drank carrot juice during their third trimester showed less aversion to carrot-flavored breakfast cereals when they started eating solid foods six months later.
This suggests that taste learning persists for months and may be more robust than auditory learning in the fetus.
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