Washington: Preterm babies are likely to experience delays in the development of the brain region linked to hearing and understanding sound, which may lead to speech and language impairments at age 2, scientists say.
"We have a pretty limited understanding of how the auditory brain develops in preterm infants," said Brian Monson, a professor at the University of Illinois in the US.
"We know from previous research on full-term newborns that not only are foetuses hearing, but they're also listening and learning," said Monson, who led the study published in the journal eNeuro.
Ultrasound studies reveal, for example, that, beginning at least as early as 25 weeks into gestation, foetuses will blink or move in response to externally produced sounds, he said.
Other research shows that newborns prefer to listen to sounds - such as music or speech - that they were exposed to in the womb over unfamiliar sounds.
Electroencephalogram studies of the brains of preterm infants show electrical activity in the auditory cortex in response to sound.
"From these types of studies, we know that foetuses in the third trimester of gestation are hearing, learning and creating memories," Monson said.
"It's pretty remarkable that such an immature system already has the ability to start distinguishing and learning," he said.
To better understand how the auditory cortex matures in the last trimester of gestation, researchers turned to a large dataset collected between 2007 and 2010.
The 90 premature infants in the study had undergone magnetic resonance imaging (MRI) one to four times.
Another 15 full-term babies were recruited and scanned within the first four days of life.
These scans were used as examples of uninterrupted foetal brain development, for comparison with the preterm babies.
The team focused on the primary auditory cortex, which is the first cortical region to receive auditory signals from the ears via other parts of the brain, and the nonprimary auditory cortex, which plays a more sophisticated role in processing those stimuli.
The analysis revealed that by 26 weeks of gestation, the primary auditory cortex was in a much more advanced stage of development than the nonprimary auditory cortex.
Between 26 weeks and about 40 weeks - the latter the equivalent of full-term birth - the nonprimary auditory cortex in the preterm infants matured quickly, partially catching up to the primary auditory cortex.
Both regions appeared less developed at 40 weeks in the preterm infants than in the full-term babies.
The team also found an association between the delayed development of the nonprimary auditory cortex in infancy and language delays in the children at age 2, suggesting that disruptions to this part of the brain as a result of premature birth may contribute to the speech and language problems often seen later in life in preemies, Monson said.