Mom’s voice plays a crucial role in boosting the neural development of an infant's brain.

A new randomized controlled trial led by Stanford Medicine has shown that exposing premature infants to recordings of their own mother’s voice can accelerate the development of brain pathways important for language processing. The findings, published in Frontiers in Human Neuroscience, provide the first causal evidence that early speech exposure can shape neural maturation in very early life.

Infants born at least three weeks earlier than term often remain hospitalized in neonatal care and receive far less maternal speech than they would in utero. Early exposure to speech plays a vital role in language acquisition and helps shape the brain regions responsible for understanding and processing spoken language.¹ Because parents cannot always stay at the hospital continuously, preemies may miss out on critical early exposure to maternal voices, a factor suspected to contribute to language delays observed later in life.²

In this trial, the researchers enrolled 46 very preterm infants (gestational ages 24–31 weeks) who were medically stable and had moved from the intensive care nursery to an intermediate care setting. Infants were randomized to either a treatment group, which received recorded maternal speech, or a control group, which received standard care without added recordings.³ Mothers recorded themselves reading a chapter of Paddington Bear in their native language; these recordings were then played overnight in 10-minute segments (twice per hour from 10 pm to 6 am), totalling about 160 minutes of extra speech exposure per night.³

Importantly, the recordings were played at night to blind parents and staff to group assignment, minimizing the chance of bias from changes in parental or caregiver behaviour.² The recordings did not appear to disturb infants’ sleep, echoing aspects of in utero auditory experience where foetuses sleep even as mothers talk.

Near the time of hospital discharge, all infants underwent MRI scanning, including diffusion MRI and relaxometry, to assess white matter microstructure in the arcuate fasciculus—a bundle of fibers strongly implicated in speech and language pathways. The left arcuate fasciculus, in particular, is known to play a dominant role in language processing.

Compared to controls, infants in the treatment group demonstrated more mature microstructural metrics in the left arcuate fasciculus: lower mean diffusivity (MD), higher fractional anisotropy (FA), and higher R1 values—each indicating more mature white matter integrity. The treatment effect was robust across multiple imaging modalities and measures. In contrast, the right arcuate showed weaker or no significant differences, consistent with known brain lateralization in language networks.³

The lead author of the research remarked that the effect was stronger than anticipated, given the relatively limited duration of the intervention. “Detectable differences in brain development even at this early stage suggest that hospital sound environments matter,” she said.

The researchers are now planning follow-up studies to test whether similar benefits apply to infants with more complex medical conditions, and to explore how the voice exposure actually works at a neural level. Meanwhile, another doctor, part of the research, is developing individualized NICU sound plans to optimize speech exposure for premature infants.

This work highlights a compelling approach: a low-cost, non-invasive intervention (maternal voice recordings) that may help mitigate language delays in children born prematurely by boosting neural development in language pathways.

References:

1. Kuhl PK. Early language acquisition: cracking the speech code. Nature reviews neuroscience. 2004 Nov;5(11):831-43.
   
   
2. McGowan EC, Caskey M, Tucker R, Vohr BR. A randomized controlled trial of a neonatal intensive care unit language intervention for parents of preterm infants and 2-year language outcomes. The Journal of pediatrics. 2024 Jan 1;264:113740.
   
   
3. Travis KE, Scala M, Marchman VA, Wu H, Dodson CK, Bruckert L, Lazarus MF, Velasco Poblaciones R, Yeom KW, Feldman HM. 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. Frontiers in Human Neuroscience. 2025;19:1673471. doi:10.3389/fnhum.2025.1673471 [2].