Mom's voice boosts brain development in premature babies

The hum of a hospital hides many quiet stories. One of them begins when a premature baby hears its mother’s voice. Scientists at Stanford Medicine have shown that those familiar sounds can do more than comfort – they can help the brain grow.

The new study offers the first solid proof that hearing a mother’s voice speeds up language pathway development in premature infants.

Early sounds and lost time

Inside the womb, a baby hears soft speech and steady rhythms from about 24 weeks of pregnancy. These early sounds tune the brain to language.

Premature birth cuts that process short. Babies in intensive care often miss the voices and patterns they would normally hear inside the uterus.

“This is the first causal evidence that a speech experience is contributing to brain development at this very young age,” said Dr. Katherine Travis, the study’s lead author.

“This is a potentially transformative way of thinking about how to approach neonatal care for promoting better language outcomes in children born prematurely.”

How premature babies heard voices

Researchers invited mothers of preterm infants to record themselves reading Paddington Bear in their native languages.

Each baby in the treatment group listened to the recordings for nearly three hours every night. A second group heard only the normal hospital sounds.

The recordings played through small devices fixed safely to the infants’ cribs. The sound level stayed below 50 decibels – soothing but never disruptive.

Nurses and parents didn’t know which babies heard the recordings, keeping the study fair.

After several weeks, every baby received MRI scans before discharge. The researchers focused on the arcuate fasciculus, a bundle of nerve fibers that links language areas in the brain.

What the scans revealed

The differences were clear. Babies who heard their mother’s voice showed more mature brain wiring on the left side – the part responsible for language.

Those who didn’t hear the recordings showed slower development in that region.

“I was surprised by how strong the effect was,” said Dr. Travis. “That we can detect differences in brain development this early suggests what we’re doing in the hospital matters. Speech exposure matters for brain development.”

Doctors also checked health data. The intervention caused no sleep problems, no breathing issues, and no delays in hospital discharge.

Brain growth in premature babies

White matter, the brain’s wiring, grows fast in the last trimester. This growth depends on experience. Myelin, the protective layer around brain fibers, thickens as the baby hears and processes sound.

The study’s MRI results showed signs of stronger myelination in babies who listened to recordings.

Dr. Melissa Scala, a neonatologist and study co-author, found the results remarkable. “Babies were exposed to this intervention for a relatively short time,” she said.

“In spite of that, we were seeing very measurable differences in their language tracts. It’s powerful that something fairly small seems to make a big difference.”

Voices support premature babies

The idea works because it’s simple. Parents record their voices once, and the hospital system plays those sounds regularly.

Even when parents can’t stay overnight, their babies still hear familiar tones and rhythms. That connection seems to support both comfort and brain growth.

The intervention is safe, low-cost, and easy to use in different hospital settings. Researchers found no harm, only signs of positive change.

Sound therapy for premature babies

Dr. Travis and her team want to test whether the same effect appears in sicker preterm babies or those with complications. They’re also curious about different speech types.

Infant-directed speech, with its musical tone, might affect the brain differently from adult conversation. Understanding that difference could help hospitals design more targeted interventions.

Future work will also explore how voice exposure affects sleep, stress, and later learning skills.

Previous research has shown that early sound therapy can calm premature infants and improve attention. These ideas may eventually shape new care routines in neonatal units.

Giving parents a role

Parents of preterm babies often feel helpless. The study gives them a new way to stay connected.

“We’ll always support parents visiting and talking to their babies in person as much as they can,” said Dr. Scala.

She added that even when parents can’t be present, their voice recordings still support their child’s growth.

“This is a way that – even if they can’t be there as much as they want to – the baby is still hearing them and still knows that they’re there,” noted Dr. Scala. “And the parents are still contributing to the baby’s brain development.”

The study is published in the journal Frontiers in Human Neuroscience.

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