Inclusion Criteria:

Clinically well infants as determined by the neonatal care team.

• Term newborns: approximately equal number of male and female newborns, gestational age 37-42 weeks and chronological age < 28 days. 
• Preterm infants: approximately equal number of male and female preterm infants, and:
• If gestational age 26-36 weeks, then chronological age 7-21 days at time of recruitment.

Exclusion Criteria: 

• Infants currently requiring continuous cardiovascular medication infusions, including but not limited to: dopamine, epinephrine, milrinone, and dobutamine (may have received these medications in the past.
• Term infants who are small for gestational age (<10th percentile for weight) at birth.
• Parent does not have custody of infant.
• History of intracranial hemorrhage.
• History of hypoxic ischemic encephalopathy or neonatal encephalopathy.