By Matthew Warren

Anyone who has stood in the supermarket aisle trying to remember their shopping list might have wished for a larger brain. But when it comes to memory, bigger isn’t always better. A study published in Neuropsychologia has found that young children whose cerebral cortex is thinner in certain areas also tend to have better working memory.

A number of previous brain imaging studies already found that working memory – which we use for remembering and manipulating pieces of information over short timescales – involves a network of brain areas in both the frontal and parietal cortices.

But most of these studies examined adults and older children, and few researchers have investigated younger children aged 4 to 6. At this age, children’s working memory usually improves drastically, so it’s important to understand what is going on in the brain, especially if this could help children with learning difficulties.

In the new study, Morgan Botdorf and Tracy Riggins from the University of Maryland scanned the brains of 189 healthy children with no known learning difficulties aged between 4 and 8. An impressive 186 of the children remained still enough during the scan to provide usable data.

In a separate session outside of the MRI scanner, the researchers also assessed the kids’ working memory using the forward digit span task, which measures how many digits a child can hold in their memory.

Botdorf and Riggins then looked at how performance on this test was related to the thickness of four brain areas known to be important in working memory: the superior frontal cortex, middle frontal cortex, superior parietal cortex, and anterior cingulate cortex. They found that in all four regions, children with thinner grey matter tended to be able to hold more numbers in memory – they had what psychologists call “a higher digit span”.

While this result might seem counter-intuitive, it is not completely unexpected that a thinner cortex in these areas is related to better memory. During development, connections between neurons are “pruned”, restructuring and streamlining the brain in a way that is thought to improve memory and cognition, and the study authors suggest that this process is taking place in their participants.

The researchers also looked at whether these key brain regions were thinner in the older children – and if so, whether this could help explain why older children generally have better working memory. One region did seem to be involved in the effects of aging on working memory: older children had a thinner anterior cingulate cortex, which in turn was related to having a higher digit span. The researchers suggest that in young children, the anterior cingulate cortex “may be developing particularly rapidly” and so have an important role in the cognitive changes that occur in early childhood.

Aside from age, a number of other factors could influence the thickness of cortical areas. Previous research has implicated genetics and lifestyle factors like vitamin consumption and stress, for example, though the researchers note that the evidence for these is often sketchy. “A ripe avenue for future research would be to focus on identifying specific factors that impact the structure of the cortex, particularly during early childhood,” they write.

With a better understanding of what causes cortical thinning, researchers could begin to figure out how to intervene to facilitate these changes and improve working memory in children at risk of memory impairments. This is an important consideration as working memory is strongly related to educational achievement at school, and so the new study is a step in the right direction.

A limitation of the new research is that it only looked at children’s ability to store verbal information, not other important functions of working memory, such as remembering visual information. It remains to be seen whether these other aspects of memory are also related to the thickness of young children’s grey matter.

—When less is more: Thinner fronto-parietal cortices are associated with better forward digit span performance during early childhood

Matthew Warren (@MattbWarren) is Staff Writer at BPS Research Digest