Adolescents and adults who were born very prematurely may have "older" brains than those who were born full term, a new study reveals.

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Researchers say that preterm birth may speed up brain maturation.

Researchers identified changes in the brain structure of adults born between 28 and 32 weeks gestation that corresponded with accelerated brain aging, meaning that their brains appeared older than those of their non-preterm counterparts.

Lead study author Dr. Chiara Nosarti, of the Institute of Psychiatry, Psychology and Neuroscience at King's College London in the United Kingdom, and colleagues recently reported their findings in the journal Neuroimage.

According to the Centers for Disease Control and Prevention (CDC), around 1 in 10 infants born in the United States in 2015 were preterm, meaning that they were born before 37 weeks of pregnancy.

A baby's brain fully develops in the final few weeks of gestation, so being born early disrupts this process. As such, babies born preterm are at greater risk of developmental disabilities including impairments in learning, language, and behavior.

But how does preterm birth affect the brain in adulthood? This is what Dr. Nosarti and colleagues sought to find out with their new study.

Preterm birth and gray matter volume

Scientists once thought that brain maturation ceases in adolescence. But in recent years, studies have indicated that this may not be the case, and that the brain may not fully mature until we reach our mid-20s.

According to Dr. Nosarti and team, their study is the first to investigate how preterm birth might affect this adult brain maturation process.

Using MRI, the researchers analyzed the brain structure of 328 adults who had been born before 33 weeks gestation. Subjects were assessed at two time points: adolescence (mean age 19.8 years) and adulthood (mean age 30.6 years).

The brain scans of these participants were then compared with those of 232 adults who were born full term (the controls), alongside 1,210 brain scans gathered from open-access MRI archives.

Specifically, the researchers looked at volume of gray matter in the participants' brains, which they say can be a marker of "brain age."

Accelerated brain maturation identified

Compared with the controls, the team found that subjects born very preterm had a lower volume of gray matter in both adolescence and adulthood, particularly in brain regions associated with memory and emotional processing.

They also pinpointed a number of structural brain alterations that demonstrated resilience to the effects of preterm birth. For example, they identified increases in gray matter volume in regions associated with behavioral control.

The team hypothesizes that such alterations may arise to compensate for other brain functions negatively impacted by preterm birth.

"Even though one can only speculate on the functional significance of these alterations, prior studies suggested that compensatory mechanisms may support cognitive and language processing in very preterm samples," write the authors.

Upon further investigation, the team found that the reduced gray matter volume identified in very preterm participants was associated with accelerated brain maturation. As a result, the brains of the preterm subjects appeared older than those of the controls.

First study author Dr. Vjaceslavs Karolis, also of the Institute of Psychiatry, Psychology and Neuroscience at King's College London, says that the team was surprised by the results.

"The finding of structural signatures of accelerated brain maturation in those born very prematurely was unexpected," he notes, "because previous research suggested delayed brain maturation at earlier stages of development."

Dr. Nosarti adds that they are unable to confirm how the structural brain changes identified in very preterm adolescents and adults translate to day-to-day functioning, but they believe that this is something that should be investigated in future research.

"Such studies could inform the development of cognitive and behavioral interventions aimed at boosting brain resilience."