Control infants with EGA of at least 24 weeks Must meet 1 of the following conditions: Requirement for stable conventional ventilator settings with respiratory index score of less than 2.5 and/or extubated within past 24 hours No requirement for mechanical ventilation Must meet all of the following conditions: AGA No congenital anomalies No medical complications, including seizures and necrotizing enterocolitis No documented sepsis by positive blood culture No supplemental oxygen use (infants 35 weeks EGA and over only)