The amount of adult speech children are exposed to in their early years may help to shape the structure of their brains, researchers say.
Now researchers say they have found a relationship between the amount of adult speech children are exposed to and the concentration of a substance in the brain – known as myelin – that surrounds nerves and makes signals more efficient.
“I think the take-home message is, absolutely talk to your kids. And it matters,” said the lead author, Prof John Spencer of the University of East Anglia. “What’s pretty striking here is that it’s literally shaping the structure of the brain.”
Writing in the Journal of Neuroscience, Spencer and colleagues describe how they used a device fitted inside a vest to record the amount of speech 87 children aged about six months and 76 aged about 30 months were exposed to at home.
The team recorded 6,208 hours of language data, finding that children with more highly educated mothers were exposed to greater amounts of adult speech, and themselves produced more vocalisations.
The team then invited 84 of the children into hospital, where they fell asleep in a special quiet room.
“Once the kids were asleep, we basically crept in like ninjas and lifted the child up and put them on to a trolley and transported them into the MRI scanning room,” said Spencer.
The team then used the MRI scans to measure the amount of myelin in the children’s brains.
As the brain develops the amount of myelin increases. However, the team found, for the 30-month-olds, larger amounts of adult speech were associated with higher quantities of myelin in language-related pathways in the brain.
By contrast, for six-month-olds, greater amounts of adult speech were associated with lower concentrations of myelin.
While the latter was unexpected, Spencer said one possible explanation is that the impact of speech depends upon the brain’s stage of development.
“When you’re six months old more input is good. But at that point, your brain is growing massively and you get this massive growth of new neurons,” he said. “So the input comes in and may help prolong that period of brain growth.”
But, Spencer noted, at 30 months the brain is in a different state. “Now, it’s starting to prune back some of the cell growth, form specific connections and that’s where myelin comes in. So now the input starts to help structure the myelin,” he said.
The researchers add the associations for both age groups were stronger, at least in the right hemisphere of the brain, for children of more highly educated mothers.
Spencer said more research is now needed, adding it is not yet clear how strongly the team’s results are linked to outcomes in children.
“The cool thing will be if the six-month-old kids who show that negative relationships turn into 30-month-old kids who show a positive relationship,” he said.
Dr Saloni Krishnan, reader in cognitive neuroscience at Royal Holloway, University of London, who was not involved in the work, said the research had produced novel findings but cautioned it does not prove more speech causes more myelination, noting the reverse was true for children aged about six months.
And questions remain. “It is not yet clear if greater myelination in these areas is meaningful for future language or cognitive development, or if this a stable pattern across childhood,” she said.
Krishnan also noted individual differences in language ability are linked to genetics.
“Children who are exposed to more language at home and have higher myelination will also have inherited genes from parents who are more linguistically able. We need to test for this potential genetic effect before we can attribute it to the linguistic environment,” she said.
“There is currently no consensus around the amount of optimum input children should receive, and caregivers should not necessarily feel pressure to talk more to their children.”