The purpose of this research study is to better understand how blood flow and metabolism change can influence brain development in the early decades of life. We will examine brain blood flow and metabolism using magnetic resonance imaging (MRI). The brain's blood vessels expand and constrict to regulate blood flow based on the brain's needs. The amount of expanding and contracting the blood vessels can do varies by age. The brain's blood flow changes in small ways during everyday activities, such as normal brain growth, exercise, or deep concentration. Significant illness or psychological stress may increase the brain's metabolic demand or cause other bigger changes in blood flow. If blood vessels are not able to expand to give more blood flow when metabolic demand is high, the brain may not get all of the oxygen it needs. In extreme circumstances, if the brain is unable to get enough oxygen for a long time, a stroke may occur. Sometimes small strokes occur without other noticeable changes and are only detectable on an MRI. These are sometimes called silent strokes. In less extreme circumstances, not having as much oxygen as it wants may cause the brain to grow and develop more slowly than it should. One way to test the ability of blood vessels to expand is by measuring blood flow while breathing in carbon dioxide. Carbon dioxide causes blood vessels in the brain to dilate without increasing brain metabolism. During this study participants may be asked to undergo a blood draw, MRI, and potential neuropsychological assessments. It is also possible that the study team will use a special mask to control the amount of carbon dioxide the participants breathe in so they don't breathe in too much.