Babies Rely on Mother’s Voice and Heartbeat To Develop Healthy Brains

When an infant is born prematurely, it tumbles into a world of cacophony.

Obstetricians usually try to shield preemies from the bright lights, harsh sounds, and pungent smells of the neonatal ICU, but few have tried to replace what these babies are largely deprived of: a mother’s voice and heartbeat.

Now, a new study led by Amir Lahav, a neuroscientist at Harvard Medical School, suggests that when premature babies are exposed to recordings of their mother’s voice and heartbeat, the functioning of their auditory cortex, the part of the brain which helps us hear, is significantly improved. The findings were published yesterday in the Proceedings of the National Academy of Sciences.

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Few studies tried to replace what premature babies are largely deprived of: a mother's voice and heartbeat.

Lahav and his colleagues asked the parents of 40 extremely premature babies born at Brigham and Women’s Hospital in Boston to participate in a month-long study that would ask whether or not sounds that a fetus would typically hear in utero could help premature babies develop normally.

Here’s Emily Underwood, writing for Science:

A fetus starts to hear at about 24 weeks of gestation, as neurons migrate to—and form connections in—the auditory cortex, a brain region that processes sound, Stromswold explains. Once the auditory cortex starts to function, a fetus normally hears mostly low-frequency sounds—its mother’s heartbeat, for example, and the melody and rhythm of her voice. Higher frequency tones made outside of the mother’s body, such as consonants, are largely drowned out. Researchers believe that this introduction to the melody and rhythm of speech, prior to hearing individual words, may be a key part of early language acquisition that gets disrupted when a baby is born too soon.

The premature babies participating in Lahav’s study were born not too long—between 25 and 32 weeks of gestation—after the start of the auditory cortex’s development, so hearing and language capabilities had likely been affected.

In an attempt to remedy that, the scientists recorded mothers of half of the infants reading Goodnight Moon and singing Twinkle, Twinkle, Little Star. They also recorded those mothers’ heartbeats through a stethoscope. They removed high-frequency sounds like consonants, since those are mostly drowned out in the womb, and projected the resulting sounds into 21 infants’ incubators for 45-minute sessions totaling three hours per day. The remaining infants received routine care.

After 30 days, Lahav looked at the ultrasound images of both groups’ brains and saw that the babies exposed to their mothers’ voices and heartbeats had thicker auditory cortices than the babies in the control group. Larger auditory cortices usually result in better hearing and language development later on in an infant’s life, so the scientists plan on tracking these babies’ progress. While further work is required to verify the results, their conclusions could help related fields understand how the brain stores speech information—for example, how children develop speech disorders—and could lead to better neonatal care for premature babies.