The rapid language-learning that typically occurs in children between 2 and 4 years old is not reflected in substantial increases in myelin levels, a nerve fiber insulator, as previously believed. By that time, the larger myelin structure is already there.
The findings, researchers say, underscore the importance of environment during this critical period for language.
“What we actually saw was that the asymmetry of myelin was there right from the beginning, even in the youngest children in the study, around the age of one,” says the study’s lead author, Jonathan O’Muircheartaigh, a postdoctoral fellow at King’s College London who is currently working in the Advanced Baby Imaging Lab at Brown University.
“Rather than increasing, those asymmetries remained pretty constant over time.”
The lab uses a specialized MRI technique to look at the formation of myelin in babies and toddlers. Babies are born with little myelin, but its growth accelerates rapidly in the first few years of life.
For the study, published in the Journal of Neuroscience, the researchers imaged the brains of 108 children between ages 1 and 6, looking for myelin growth in and around areas of the brain known to support language.
While asymmetry in myelin remained constant over time, the relationship between specific asymmetries and language ability did change. To investigate that relationship, the researchers compared the brain scans to a battery of language tests given to each child in the study. The comparison shows that asymmetries in different parts of the brain appear to predict language ability at different ages.
“Regions of the brain that weren’t important to successful language in toddlers became more important in older children, about the time they start school,” O’Muircheartaigh says. “As language becomes more complex and children become more proficient, it seems as if they use different regions of the brain to support it.”
A helpful baseline
Interestingly, the association between asymmetry and language was generally weakest during the critical language period.
“We found that between the ages of 2 and 4, myelin asymmetry doesn’t predict language very well,” O’Muircheartaigh says. “So if it’s not a child’s brain anatomy predicting their language skills, it suggests their environment might be more influential.”
The researchers hope this study will provide a helpful baseline for future research aimed at pinpointing brain structures that might predict developmental disorders.
“Disorders like autism, dyslexia, and ADHD all have specific deficits in language ability,” O’Muircheartaigh says. “Before we do studies looking at abnormalities we need to know how typical children develop. That’s what this study is about.”
“This work is important, as it is the first to investigate the relationship between brain structure and language across early childhood and demonstrate how this relationship changes with age,” says Sean Deoni, assistant professor of engineering, who oversees the lab.
The National Institutes of Mental Health and the Wellcome Trust funded the study.
Source: Brown University