Researchers have found that in the context of preterm birth, the brain cells fail to mature, resulting in low oxygen levels in the brain causing hypoxia. 

A brief 30-minute period of hypoxia is enough to disrupt the structure and function of the brain region hippocampus, which is vital for learning and memory. The study was published in the 'Journal of Neuroscience'. "Our findings raise new concerns about the vulnerability of the preterm brain to hypoxia. They are concerning for the long-term impact that oxygen deprivation can have on the ability of these preterm babies to learn as they grow to school age and adulthood," said the study's principal investigator Stephen Back. 

In the neonatal intensive care unit, preemies can experience up to 600 short, but impactful periods of hypoxia each week. Consequently, more than one-third of babies who survive preterm birth are likely to have smaller brains, presumably due to brain cell loss, compared with the brains of full-term infants. This can increase the risk of significant life-long neurodevelopmental challenges that will affect learning, memory, attention, and behavior. 

Using a twin preterm fetal sheep model, Back and colleagues studied the impact of both hypoxia alone, as well as in combination with ischemia (insufficient blood flow) on the developing hippocampus. The results confirm that similar to human preterm survivors, the growth of the hippocampus is impaired. However, brain cells do not die as previously believed. Rather, hippocampal cells fail to mature normally, causing a reduction in long-term potentiation, or the cellular basis of how the brain learns. 

"Remarkably, the severity of the hypoxia predicted the degree to which cells in the hippocampus failed to mature normally," explained Back. These findings are all the more unexpected because it was not appreciated that the preterm hippocampus was already capable of these learning processes.