The brain starts listening before birth, just over halfway through a 40-week gestation.1 Compared to full-term infants, premature babies, or preemies, born before 32 weeks hear far less speech from their caregivers during early development because of time spent in the neonatal intensive care unit (NICU). This lack of speech exposure may affect their language development later in life.2
Researchers at Stanford University played voice recordings of preemies’ mothers reading stories to them to find out whether it affected how their brains developed. The team observed changes in the brain’s white matter, indicating increased maturation and connectivity among preemies who heard more of their mothers’ voices. The results, published in Frontiers in Human Neuroscience, suggest that preemies’ parents can still contribute to their brain development, even when they can’t be beside their crib.3
Study author Katherine Travis, a neuroscientist at Weill Cornell Medical School and Burke Neurological Institute, called the results “the first causal evidence that a speech experience is contributing to brain development at this very young age,” in a press release.
Premature Babies Hear Less Speech
Previous studies have presented evidence that reduced speech exposure in the NICU could affect preemies’ brain development and that boosting the amount they hear from their parents could help.4
To test this hypothesis, Travis and her team conducted a randomized controlled trial. The researchers enrolled 46 preemies, and divided them into two groups. The researchers played the test group audio recordings of their mothers reading the first chapter of the children’s classic Paddington Bear. The control group did not hear recordings of their mothers’ voices.
On average, babies listened to recordings for roughly two weeks before they were discharged from the hospital. Before the babies left, the researchers imaged their brains using a magnetic resonance imaging (MRI) scanner while they slept.
Altering a Key Language Pathway in the Brain
The scans showed significant differences in the test group babies’ left arcuate fasciculus. This brain area, which is important for language processing, was more mature in the infants who heard their moms’ voice compared to those who didn’t.5
The authors were surprised by the size of the effects. “Babies were exposed to this intervention for a relatively short time,” said study co-author Melissa Scala, pediatric researcher at Lucile Packard Children’s Hospital Stanford. “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.”
Travis said that the findings should have implications for the care of these most vulnerable infants. “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,” she concluded.
- Hepper PG, Shahidullah BS . Development of fetal hearing. Arch Dis Child Fetal Neonatal Ed.. 1994;71(2), F81-F87.
- Monson BB, et al.. Language exposure for preterm infants is reduced relative to fetuses. J Pediatr. 2023;262, 113344.
- Travis KE, et al. Listening to mom in the neonatal intensive care unit: A randomized trial of increased maternal speech exposure on white matter connectivity in infants born preterm. Front Hum Neurosci. 2025.
- Inder TE, et al. Defining the neurologic consequences of preterm birth. N Engl J Med. 2023;389(5):441-453.
- Ivanova MV, et al. Functional contributions of the arcuate fasciculus to language processing. Front Hum Neurosci. 2025;15:672665.
