Children who are exposed to more words tend to develop better language skills. In one study, for example, children of caregivers who used more diverse vocabulary and syntax had bigger vocabularies. In another, infants who heard more child-directed speech became more efficient at processing familiar words by age two. And these links can be long-lasting: 25-month-olds who processed language faster were shown to have better linguistic and cognitive abilities as eight-year-olds.
A recent study, however, has gone further in investigating the potential impact of early language exposure. By examining everyday speech patterns that children hear as well as brain scans of 6- and 30-month-olds, researchers have learned about how the amount of language a child hears may be shaping physical brain structure.
“It has been well established, in the last 10 years or more, that linguistic input is good for children’s later language abilities,” says Laia Fibla, one of the study’s co-authors and a postdoctoral researcher in psychology at Montreal’s Concordia University. “But our question was also, ‘What’s the impact on the brain?’.”
How might hearing more language shape the brain?
To find out, Fibla and the other researchers looked at the amount of myelin in children’s brains. Myelin is a fatty tissue that sheaths neurons, both protecting them and helping messages to travel faster. If you think of neurons as links of a bike chain, Fibla says, myelin is the oil – it makes the gears run more quickly, efficiently, and smoothly.
The brain develops quickly in the first months of life: About a third the size of an adult’s at birth, it reaches 80% of adult brain size by age two. That makes this period an especially interesting window into how, and where, myelin grows, according to Fibla. In particular, the researchers hypothesised that children who heard more language would have more myelin in their brains.
This hadn’t been examined in such young children before. Previous research into myelin and language included no participants younger than four years, not least because of the challenge of keeping small children still in an MRI machine for 40 minutes while their brains are scanned.
For the study, the research team set up a nursery, and parents brought their children in at bedtime and put them to sleep. Soundproof headphones were put on the children – the scanner is noisy – who were then carefully lifted, sleeping, into the MRI machines. The children also wore a sound recorder, fitted into a vest, to record how much speech they were hearing on an everyday basis.
As expected, hearing more language was linked to more myelin in the 30-month-olds. “The number of words a child had been exposed to was a really strong predictor,” Fibla explains. The children who heard more words had more myelin particularly in the parts of the brain related to language.
“The children who heard more words had more myelin particularly in the parts of the brain related to language.”
Interestingly, this wasn’t true of the 6-month-olds. In fact, surprisingly, hearing more words was linked to less myelin. There could be a few reasons for that unexpected finding, Fibla says.
“At six months old, the brain has this massive explosion of myelination,” she points out. “Babies are learning so much. It’s a period of extreme activity. And at 30 months the brain is more specialised. So it could be that the brain is treating input in different ways, depending on the child’s stage of development.” In other words, at 6 months, when “everything is important”, and not just language, myelin may be spread more evenly throughout the brain.
The study doesn’t prove that hearing more language caused the increase in myelin; it only shows correlation, not causation. The researchers also found, for example, that more educated mothers tended to speak more to their children. Perhaps it is parental education level – rather than the number of words spoken to the child – that affects myelin growth. Genetics could play a role, too: The child of a parent with more innate verbal aptitude may have inherited the same characteristics. The same question applies to past research showing links between a child’s language exposure and later language skills.
But Fibla and the other researchers in this study don’t believe that parental education or genetics are the full explanation. “The association with maternal education is not as strong as the association with the amount of language input,” she says.
What do these links mean for future research and for caregivers?
If language input can shape the structure of the brain, does additional myelin then lead to better language skills? Children’s outcomes, after all, are probably what caregivers are most interested in – not the structure of the children’s brains per se. And researchers can’t draw relevant conclusions from this study alone. “We were not able to determine whether more input is related to more myelin and more language comprehension. That’s something we want to investigate in the future,” Fibla says. “That’s the next step to understanding: Is hearing more language really translating into more language ability?”
“While quantity of language is important, quality is as well.”
Regardless, particularly in the context of prior research that has shown how important early language input is for a child’s developing language skills, Fibla believes there are key takeaways for caregivers. One is that while quantity of language is important, quality is as well. For example, rather than simply switching on the television – which could technically provide lots of language “input” into a child’s brain – it appears to be more effective to engage in a face-to-face verbal interaction, or talk about something the child is interested in.
These questions of quantity versus quality, and what types of language input are most helpful for children, are areas Fibla and her colleagues would like to study further. “There’s still so much to look into. But it’s exciting that we have started to find ways to look more closely at these really unexplored age ranges, and see how different parts of the equation play a role,” she says.