Incubators branded 'neurodevelopmental dungeons' for babies
Premature babies in incubators grew larger brains after being exposed to the recorded sounds of their mothers' voices and heartbeats, a study has found.
Tests also showed that they were better at focusing on sounds than premature babies receiving routine care.
The findings highlight the fact that an incubator is a "neurodevelopmental dungeon" where a baby's natural brain development is stunted, said lead researcher Dr Amir Lahav, from Harvard Medical School in the US.
Previous studies had shown that children born prematurely often have difficulty listening and paying attention in noisy environments.
In the classroom, for instance, they might find it hard to pick up on what the teacher is telling them.
Dr Lahav's research suggests that much of the problem stems from their early experience in the neonatal intensive care unit (Nicu).
Instead of the muffled low frequency womb sounds of their mothers, their primary sound source is the noisy fan of the incubator.
"What inspired us to go into this work was the fact that when we look at how premature babies are doing later in life .. those babies too often will have a wide variety of developmental issues down the road that are all related to auditory function in some way or another," said Dr Lahav.
"We see a very high likelihood in those premature babies of having language deficits, auditory processing disorders, and attention deficits.
"This has made us wonder if the hospital environment in the neo-natal intensive care unit (Nicu) is indeed optimal for the brain development of these babies.
"We came to realise that the hospital environment that we have for those very premature babies doesn't match the developmental needs of the baby.
"Inside the incubator there isn't much auditory stimulation available for the baby, it's more like a deprived environment or a social cage, or neurodevelopmental dungeon, where the baby is basically being placed in a seemingly protected secure environment but the environment doesn't give the brain the mother's voice and heartbeat sounds that are so essential .. for the brain to mature and develop."
His experiment involved recording the heartbeats and voices of mothers of premature babies and playing them back to the infants for three hours a day during the first month of life. The sounds included the mothers singing, reading a story, and speaking "baby talk" as if engaging with their infants.
Those babies turned out to be significantly advantaged over other premature babies looked after in the normal way and not exposed to the sounds.
Not only did they weigh more - putting on an extra two grams per kilogram of bodyweight per day - but head ultrasounds showed the sound-processing region of their brain, the auditory cortex, was larger.
They were also better than non-sound exposed babies at focusing on human voices - and not just those of their mothers.
This ability was tested by looking at how their pupils dilated, a sign of mental attentiveness in babies.
Dr Lahav described the work at the annual meeting of the American Association for the Advancement of Science (AAAS) taking place in Washington DC.
He said: "The primary stimulation the (premature) baby gets in the incubator is the noise of the incubator's fan. The hypothesis here is if the primary stimulation that you are exposed to in the most critical period for auditory brain development is white noise, what you are essentially teaching the brain is to perceive noise in the foreground instead of in the background.
"Fast forward to third grade in the classroom and you have that very premature baby who is really having trouble and difficulty to attend to what the teacher is saying in a noisy environment because his brain cannot help it. It was wired in a way that noise for him is being perceived much louder and he cannot differentiate optimally.
"We found those babies who received the daily added exposure to mother's voice and heartbeat sounds in the incubator performed much better. For us this was an encouraging result - to see that we are actually influencing how the brain is going to function and handle those basic auditory skills."