Resolving the transition from negative to positive blood oxygen level-dependent responses in the developing brain

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 11; pp. 4380 - 4385
• Main Authors: Kozberg, Mariel G., Chen, Brenda R., DeLeo, Sarah E., Bouchard, Matthew B., Hillman, Elizabeth M. C.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences 12.03.2013; National Acad Sciences
• Subjects: adulthood; adults; Age groups; Animals; Arteries; Biological and medical sciences; Biological Sciences; blood; Blood flow; Blood pressure; Brain; Cerebral Cortex - blood supply; Cerebral Cortex - growth & development; Cerebral Cortex - metabolism; Cerebrovascular Circulation - physiology; child development; Circulatory system; Fundamental and applied biological sciences. Psychology; Hemodynamic responses; Hemodynamics - physiology; humans; Hyperemia; image analysis; Imaging; Infants; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; neonates; NMR; Nuclear magnetic resonance; Oxygen; Oxygen - metabolism; Oxygen consumption; Oxygen Consumption - physiology; postnatal development; Rats; Rats, Sprague-Dawley; Rodents; Signal transduction; vasoconstriction; Vertebrates: nervous system and sense organs; brain development; Central nervous system; Development; neurovascular coupling; Self regulation; Stimulation; vascular compartments; autoregulation; somatosensory stimulation; Encephalon
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1212785110

The adult brain exhibits a local increase in cortical blood flow in response to external stimulus. However, broadly varying hemodynamic responses in the brains of newborn and young infants have been reported. Particular controversy exists over whether the "true" neonatal response to stimulation consists of a decrease or an increase in local deoxyhemoglobin, corresponding to a positive (adult-like) or negative blood oxygen level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI), respectively. A major difficulty with previous studies has been the variability in human subjects and measurement paradigms. Here, we present a systematic study in neonatal rats that charts the evolution of the cortical blood flow response during postnatal development using exposed-cortex multispectral optical imaging. We demonstrate that postnatal-day-12-13 rats (equivalent to human newborns) exhibit an "inverted" hemodynamic response (increasing deoxyhemoglobin, negative BOLD) with early signs of oxygen consumption followed by delayed, active constriction of pial arteries. We observed that the hemodynamic response then matures via development of an initial hyperemic (positive BOLD) phase that eventually masks oxygen consumption and balances vasoconstriction toward adulthood. We also observed that neonatal responses are particularly susceptible to stimulus-evoked systemic blood pressure increases, leading to cortical hyperemia that resembles adult positive BOLD responses. We propose that this confound may account for much of the variability in prior studies of neonatal cortical hemodynamics. Our results suggest that functional magnetic resonance imaging studies of infant and child development may be profoundly influenced by the maturing neurovascular and autoregulatory systems of the neonatal brain.