The Earliest Fetal Memory?

Researchers have found short-term memory in fetuses as early as 30 weeks.

Like any prospective mom, as 21-year-old Angela Morton goes through her first pregnancy the family stories of her own baby years begin to emerge -- including her mother's trick of calming her with Aerosmith's 1988 song "Angel" anytime she was a fussing as an infant.

"That was the song for me I guess," said Morton. "But I've never even heard it since I was a baby."

Morton's mother may have discovered a secret infant-soothing property in Steven Tyler's rock ballads. Or, more likely, she was was playing on an aspect of fetal memory outlined by researchers in Tuesday's issue of the journal Child Development.

In a study of 100 of pregnant women in the Netherlands, researchers say they found evidence that fetuses have short-term memory of sounds by the 30th week of pregnancy, and develop a long-term memory of sound after that.

The researchers documented the memory by watching fetal movements with ultrasound while they played "vibroacoustic" sound to the growing baby. Five of the fetuses in the study did not move in reaction to the sound and were eliminated from the study.

But among the fetuses who did move, researchers repeated the sound until the fetus "habituated" to it and no longer reacted. Doctors let some time pass and then tested the memory of the fetus by playing the sound in intervals to see if the fetus "remembered" or recognized the sound and did not react.

The study found that by 30 weeks of age, a fetus could "remember" a sound for 10 minutes. By the 34th week a fetus may be able to "remember" the sound for four weeks.

Morton thought that same sort of memory could have been why she was calmed by Steven Tyler as an infant.

"She [Morton's mother] used to go play it when she pregnant and sing along… then when I was fussy as a baby she used to play it and I calmed down," she said.

Right now Morton mostly plays Christian rock and The Beatles for her baby boy Christian, who is due in November. She says she's thinking about expanding the music collection for her baby in case there is more to this research.

Recognizing Memory in the Womb

While researchers have long documented "habituation" of the fetus -- an experiment with car horns and pregnant women in the 1920s was the first to do so -- child development specialists might not all agree that this is a form of memory as everyday people think of it.

"In this case, they appear to be study a very primitive type of memory called habituation or sensitization which is the tendency of animals to stop responding to a repeated stimulus," said Mark Strauss, autism researcher and associate professor at the University of Pittsburgh wrote in an e-mail to ABCnews.com.

"It is already known that a fetus will habituate to a stimulus. Indeed, even just a single muscle cell that is stimulated by an electrical stimulus will stop contracting, indicating a type of memory," said Strauss.

But Strauss was intrigued that the fetal memory could last that either 10 minutes, or even four weeks, as the researchers suggested.

"What is critically important to recognize, however, is that these memories are not conscious or introspective voluntary memories they way an older child or adult thinks about past experiences," said Strauss. "They are very different and, indeed, involve lower areas of the brain that are very different from high-level brain area."

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