Put on your shoes and jacket, then grab your lunch bag and turn off the lights – sounds simple, right? But to a 5-year-old, this multi-step process could be tricky to follow, especially if the child is distracted. What’s at play here is working memory – holding things in your mind that you can’t see. A new study has found that children actually recruit similar brain areas as adults for working memory but have a lower capacity for remembering multiple things at once.
People use working memory all the time every day, whether trying to remember to go pick up the dry cleaning while looking up something online, or remembering a friend’s coffee order while walking up to the counter to buy it. Some studies have found that by age 12 to 13, working memory capacity is very similar to that of young adults, with peak working memory capacity reached in late adolescence/young adulthood.
Although scientists have known for some time that adults have a stronger working memory than children, they have not understood the parts of the brain involved in this difference. “Pretty much every parent can tell you that a 5-year-old child is less good at remembering things for a few seconds than the parent,” says Maria Kharitonova of Northwestern University. “But every parent will also tell you that their 5-year-old can hold things in mind for a few seconds, particularly if they’re not distracted.”
So the question Kharitonova, along with senior researcher Margaret Sheridan and colleague Warren Winter of Boston Children’s Hospital, wanted to explore was: how does a child’s working memory work? “Previous work pointed to the fact that children used their prefrontal cortex less than adults,” she says. “But we wondered, why? And if they’re really not using their prefrontal cortex, but they are remembering things, what part of the brain are they using?”
In their new study, the researchers asked adults and children, ages 5 to 8, to lie in an fMRI scanner and look at a different colored dots on a computer screen. Every few seconds, they would see different numbers of dots and need to identify later if the a new dot was the same or different color than the previous ones seen.
“This was easy for adults, they could pretty reliably remember up to 4 dots,” Kharitonova says. “But for young kids this was really hard.”
Says Sheridan: “No one had done a task like this in the scanner with children as young as 5, and so we did not know what their brains would look like in response to this task. The answer turned out to be simple.”
As published in May in the Journal of Cognitive Neuroscience, while children generally maxed out at remembering 1 to 2 colors, they were using their prefrontal cortex just as much as the adults remembering 4 colors. Past studies have failed to equate for differences in working memory capacity.
“But that wasn’t the whole story,” Kharitonova says. “Children also just activated some other areas less, like the parietal cortex. They increased activation as the task got more difficult, but they never got to adult levels.”
The study is the first to investigate the neural correlates of a working memory task in children this young. This age range, 5 to 8 years old, Sheridan says, “is a really important one for the development of ‘cognitive control’ or ‘executive functioning’ skills, of which working memory is one component. It’s also an important period for the emergence of certain kinds of clinical problems which are related to executive function, such as attention-deficit/hyperactivity disorder (ADHD).”
Indeed, Sheridan and Kharitonova have just collected data on this same task in a group of children with ADHD to compare to typical development of working memory. “Every time research like this is completed we learn a little more about how kids’ brains develop,” Sheridan says. “This knowledge will inform prevention and intervention work for children with clinical problems. But this work can also tell us about how to interact with and teach our own children. Next time your 6 year old forgets the 3 things you told him, try telling him only 1 or 2!”
-Lisa M.P. Munoz