Spatial variation in the hemoglobin phase of oxygenation and deoxygenation in the developing cortex of infants.

Spontaneous low-frequency oscillatory changes in oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) are observed using functional near-infrared spectroscopy (fNIRS). A previous study showed that the time-averaged phase difference between oxy-Hb and deoxy-Hb changes, referred to as hemoglobin phase of oxygenation and deoxygenation (hPod), is sensitive to the development of the cortex. We examined phase-locking index of hPod, referred to as [Formula: see text], in addition to hPod, in neonates and 3- and 6-month-old infants using the 94-channel fNIRS data, which covered large lateral regions of the cortex. The results showed that (1) developmental changes in hPod exhibited spatial dependency; (2) [Formula: see text] increased between the neonate group and 3-month-old infant group over the posterior, but not anterior, regions of the cortex; and (3) the cortical regions of each age group were clustered in several domains with specific characteristics of hPod and [Formula: see text]. This study indicates that the neonatal cortex is composed of regions with specific characteristics of hPod and [Formula: see text], and drastic changes occur between the neonatal period and 3 months of age. This study suggests that hPod and [Formula: see text] are sensitive to the cortical region-specific development of the circulatory, blood flow, metabolic, and neurovascular functions in young infants.