Teenagers who were born preterm have brain development problems that directly affect their capacity to learn and remember information, says a new study.

Researchers at University of Adelaide found that children born before 37 weeks of gestation had reduced plasticity in the brain.

"Plasticity in the brain is vital for learning and memory throughout life. It enables the brain to reorganize itself, responding to changes in environment, behavior and stimuli by modifying the number and strength of connections between neurons and different brain areas. Plasticity is also important for recovery from brain damage," Dr Julia Pitcher from the University of Adelaide's Robinson Institute said.

Preterm babies are at higher risk of learning disabilities, cerebral palsy, problems associated with breathing, vision and hearing loss and digestive problems, says the National Institutes of Health.

Past research has shown that preterm-born children have motor, cognitive and learning problems, Pitcher said. Being born even slightly prematurely affects the structure of the brain.

The mechanisms that link poor brain development due to premature birth and behavioral problems like learning aren't known yet, Pitcher added.

For the study, researchers compared brain scans of teens born preterm to those who were born after full term.

"Teenagers born preterm clearly showed reduced neuroplasticity in response to brain stimulation. Surprisingly, even very modest preterm birth was associated with a reduced brain response. On the other hand, term-born teenagers were highly 'plastic' compared with adults and the preterm teens," Dr Pitcher said.

Around 15 million babies are born preterm every year, and the numbers are rising, says the World Health Organization. India, Nigeria and the U.S. top the list of countries with the most preterm births.

Researchers also measured levels of cortisol, normally produced in response to stress, to understand the chemical and hormonal differences between the groups.

"Preterm teens also had low levels of cortisol in their saliva, which was highly predictive of this reduced brain responsiveness. People often associate increased cortisol with stress, but cortisol fluctuates up and down normally over each 24-hour period and this plays a critical role in learning, the consolidation of new knowledge into memory and the later retrieval of those memories. This might be important for the development of a possible therapy to overcome the neuroplasticity problem," Dr. Pitcher added.