Despite improved survival rates of infants, higher brain dysfunction in surviving infants remains a considerable problem. Most infants with higher brain dysfunctions are born preterm. Magnetic resonance imaging (MRI) is a useful tool to detect structural brain damage and provides important information to evaluate the neurologic sequelae of such preterm infants. AlthoughMRI can reveal detailed brain structure, it is not the best option to assess brain function in preterm infants because of various restrictions. To overcome this difficulty, a new imaging technique, called functional near infrared spectroscopy (fNIRS), can be used to evaluate brain function in preterm infants. fNIRS is a suitable method to examine infants because, unlikeMRI, it is not necessary to restrict movement and it is silent. In this review, we focus on language function, an important higher human brain function and one of the most prominent difficulties among grown preterm infants. We describe the development of speech perception in infants from preterm to age 1 year. First, we discuss the development of the brain hemodynamic response to speech stimulation in full-term infants, imaged using fNIRS. Second, we discuss the functional specialization in full-term infants for speech processing in the cerebral cortex as revealed by fNIRS. Third, we discuss potential interpretations of developmental changes in brain activation during speech perception in preterm infants. We present data that reveal the development of speech processing in full-term and preterm infants. We conclude that fNIRS can aid in the anticipation of language delay in preterm infants and may facilitate early intervention and treatment of such dysfunctions.
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