Abstract
Functional magnetic resonance imaging (fMRI) has become a premiere technique for studying the development and neural mediation of a wide range of typical and atypical behaviors in children. While the mechanism of the blood oxygen level-dependent (BOLD) fMRI signal has been a focus of investigation in the mature brain, it has been largely unexamined in the developing brain. One critical component of the BOLD signal that has been noted to change with age is cerebral blood flow (CBF). Reports of CBF in children based on clinical radioactive tracing methods have found elevated CBF in childhood relative to adulthood, which could affect the BOLD response. This study used non-invasive arterial spin labeling magnetic resonance imaging to study resting state and activity-driven CBF in conjunction with the functional BOLD response in healthy children 8 and 12 years of age and in adults. Participants performed a finger-tapping task to generate robust activation measured in the motor cortex. Quantification of resting state CBF demonstrated higher CBF in 8 year olds and in 12 year olds relative to adults. The absolute increase in CBF between baseline rest and peak response during the motor task was also higher in both child groups compared to adults. In contrast, the relative increase of CBF above baseline, expressed as percent of CBF change, was comparable across groups. The percent of BOLD signal change was also stable across age groups. This set of findings suggests that along with elevated CBF in childhood, other component processes of the BOLD response are also in an elevated state such that together they yield a net BOLD effect that resembles adults. These findings coincide with our previous examination of hemodynamics in primary sensory cortex. Although the magnitude of the BOLD response appears consistent between childhood and adulthood, the underlying physiology and cerebrovascular dynamics that give rise to the BOLD effect differ between immature and mature neural systems.
Highlights
Over the last decade, there has been a rapid increase in the number of scientific investigations employing blood oxygen level-dependent (BOLD) functional magnetic resonance imaging to study brain development in vivo
Our group has recently reported results of an Arterial spin labeling (ASL) investigation of Cerebral blood flow (CBF) development and BOLD signal dynamics in the auditory cortex, where we found elevated resting and activity-driven CBF in healthy children compared to adults; a concomitant age-related difference in the magnitude of the BOLD response was not detected (Moses et al, 2013)
A one-way analysis of variance (ANOVA) comparing resting state CBF between the age groups showed a main effect of age, F(2,25) = 8.37, p < 0.002
Summary
There has been a rapid increase in the number of scientific investigations employing blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to study brain development in vivo. Cerebral blood flow (CBF) plays a key role in the BOLD signal, since it directly influences proportions of oxygenated and deoxygenated blood in the resting and active brain. The characteristic increase in BOLD signal observed during cognitive stimulation occurs, in part, due to an increase in CBF, a physiological parameter within the brain that is significantly elevated in children during the first two decades of life relative to adult levels (Chugani and Phelps, 1986; Ogawa et al, 1989; Chiron et al, 1992; Kuroda et al, 1993; Barthel et al, 1997; Takahashi et al, 1999). Baseline differences in CBF rates between children and adults have the potential to produce an agerelated confound in the BOLD signal, which would be of critical significance to the growing field of developmental neuroimaging
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