How fast a baby's brain grows, rather than how large it is, predicts the child's mental abilities later in life, a new study of preterm infants suggests.
The faster the brain's cerebral cortex grew during the first months of life, the higher the children scored at age 6 on intelligence tests designed to measure their abilities to think, speak, plan and pay attention, the researchers found.
The cerebral cortex is an outer layer of the brain that is critical for language, memory, attention and thought.
The study found no relationship between the size of a baby's brain and the child's later test scores.
While it's not clear whether the results would also apply to babies born full-term, researchers said the findings are helping them understand what might go wrong in the brains of preterm babies that causes many of those infants to experience cognitive problems later in life.
"It points us to the fact that the period before normal birth is a critical time for brain growth," said study researcher David Edwards, a professor of neonatal medicine at Imperial College in London. Anything that disrupts this growth, including preterm birth or certain illnesses, may reduces cognitive abilities, Edwards said.
Edwards and colleagues examined 82 infants born before 30 weeks of gestation. (Full-term pregnancies generally last between 38 and 42 weeks.) The researchers used magnetic resonance imaging to scan the brains of the tiny babies almost immediately after birth — when some of whom weighed less than 1.5 pounds (700 grams) — and again up until the date they would have been born if the pregnancy had been full-term. None of the babies had been born with noticeable brain damage.
Some babies had their brains scanned only once, some two or three times, and some as many as eight times over the course of the study. (MRIs use magnetism, not radiation, to create images of the brain, so the babies in this study weren’t at risk for harmful side effects from the imaging.)
The children took intelligence tests when they were 2 and 6 years old.
The growth rate of the cerebral cortex in infancy was linked, in particular, to scores on tests that measured attention, language, memory, planning and the ability to conceptualize numbers. Babies whose cerebral cortices grew 5 to 10 percent less than those of other babies scored lower than average on the intelligence tests at age 6.
The results were true regardless of the children's social class. However, it's possible that factors other than brain growth ? such as the interaction between the child and his or her family ? influenced test scores, Dr. Peter Rosenberger, of Massachusetts General Hospital, and Heather Adams, of the University of Rochester Medical Center, wrote in an editorial accompanying the study.
The findings may help researchers know if therapies intended to treat preterm infants will help them later in life, the study said. If a treatment increases the growth of the cerebral cortex, then it could reduce the risk of cognitive problems in childhood.
The study and editorial were published today (Oct. 12) in the journal Neurology.