Study Explains Why Human Children Grow Slowly
A toddler's brain uses up twice as much glucose as an adult's brain, a new study shows. The researchers say that the finding explains why human babies take so much time to grow as compared to other animals.
According to researchers at the Northwestern University, the brain uses a huge part of the body's energy in the early years. This uneven energy-use lets the brain develop at a faster rate than the body.
"Our findings suggest that our bodies can't afford to grow faster during the toddler and childhood years because a huge quantity of resources is required to fuel the developing human brain," said Christopher Kuzawa, first author of the study and a professor of anthropology at Northwestern's Weinberg College of Arts and Sciences. "As humans we have so much to learn, and that learning requires a complex and energy-hungry brain."
For the study, the researchers used PET and MRI brain scan data to look at glucose uptake and brain volume, respectively. The team wanted to find when the brain takes up most energy. The data showed that this brain drain is highest at about 4 years of age. During this time, the body shows minimum growth, while the brain forms several networks.
The team estimates that during this critical period, the brain uses resources at a rate "equivalent to 66 percent of what the entire body uses at rest."
The study provides evidence for the idea that human babies take a long time to grow as their brains use most of the energy.
The researchers said that the current study also explains some common observations made by parents.
"After a certain age it becomes difficult to guess a toddler or young child's age by their size," Kuzawa said in a news release. "Instead you have to listen to their speech and watch their behavior. Our study suggests that this is no accident. Body growth grinds nearly to a halt at the ages when brain development is happening at a lightning pace, because the brain is sapping up the available resources."
Previous research has shown that human babies are born with several brain networks. With time, the brain prunes these synapses and improves efficiency of the networks.
The study is published in the journal Proceedings of the National Academy of Sciences.