In the US, every year approximately 30,000 infants are born very prematurely, with birth weight less than 1000 grams. These infants usually require ventilators to help them breath normally during the first few weeks of life. Although the ventilator is lifesaving, it can also injure the very fragile lungs of these infants. Thus, a ventilation strategy, called permissive hypercapnia (high carbon dioxide), is widely used to prevent lung injury. Importantly, there is new research showing that high carbon dioxide may cause brain injury. In our proposed research, we will use magnetic resonance imaging methods to evaluate the brain in 40 very premature infants at term−equivalent age (Half of them had permissive hypercapnia ventilation, the other half did not) to see if permissive hypercapnia has adverse effect on brain development.