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Description
Increasingly, researchers in the field of developmental cognitive neuroscience use blood oxygen level dependent (BOLD) functional magnetic resonance imaging (FMRI) to investigate brain activity in children. However, the BOLD signal is dependent on changes in several underlying physiological processes, namely cerebral blood flow (CBF). Few studies have been conducted that systematically examine age-related changes in CBF and the BOLD signal in the developing brain. Previous research using radionucleotide tracing techniques with pediatric patient populations have found that children have increased levels of resting CBF relative to adults. These findings raise the question of whether or not age-based differences in baseline CBF lead to age-related differences in the BOLD signal. If so, observed differences in the BOLD response between children and adults might be mistakenly attributed to developmental differences in cognitive processes when they may actually originate from differences in CBF. More recently, an MRI technique called arterial spin labeling (ASL) has been developed, which allows researchers to noninvasively assess CBF during both rest and functional tasks in typical children. The present study used ASL to concurrently assess CBF and BOLD signal change in auditory cortex in two groups of healthy, non-anesthetized children (8 year olds and 12 year olds) and adults. Participants underwent an FMRI scan while listening to instrumental music to elicit activation in the auditory cortex. Cardiac and respiratory effort were recorded throughout. The study focused on the hemodynamics in primary auditory cortex in an anatomically defined region of interest (ROI) analysis. Within and between runs, images were coregistered, corrected for cardiac and respiratory contributions to the signal, and then averaged. Voxels within the ROI that correlated significantly with the hemodynamic reference waveform contributed to four indices for each subject: resting CBF, absolute change in CBF, and percent of CBF and BOLD signal change between rest and auditory stimulation. One-way analysis of variance was used for age group comparisons of these indices. Results show that 8-year-old and 12-year-old children had significantly higher resting CBF than adults, confirming findings from previous studies utilizing invasive methods. The absolute difference in CBF between rest and listening to music was greater in children as well. No significant differences were observed in CBF indices between the two groups of children. Despite age-related changes in resting and absolute difference in CBF, the percent of change between rest and auditory stimulation in CBF and the BOLD signal were not significantly different between groups. v The current study presents evidence that increased resting and activity-driven CBF does not coincide with the amount of BOLD signal change between rest and activity. These results suggest that another process, namely oxygen metabolism, is also likely to be upregulated in the young brain. Future examination of oxygen metabolism in the auditory cortex, in addition to investigations of CBF and the BOLD signal in other areas of the brain, will lead to a more comprehensive understanding of developmental changes in cerebral hemodynamics. Results from the current study will enable neurodevelopmental researchers to better interpret developmental changes in the BOLD signal.
