Infant brain controls blood flow differently

?The control of blood flow in the brain is very important,? says Elizabeth Hillman, associate professor of biomedical engineering and of radiology, who led the research study in her Laboratory for Functional Optical Imaging at Columbia University.

?Not only are regionally specific increases in blood flow necessary for normal brain function, but these blood-flow increases form the basis of signals measured in fMRI, a critical imaging tool used widely in adults and children to assess brain function,? says Hillman. ?Many prior fMRI studies have overlooked the possibility that the infant brain controls blood flow differently.?

Functional magnetic resonance imaging, or fMRI, is one of several brain-imaging methods that measure changes in blood flow to detect the presence and location of neuronal activity. In adults, blood-flow increases occur in specific regions of the brain during a particular task like moving your hand or reacting to a stimulus.

?We found that the immature brain does not generate localized blood-flow increases in response to stimuli,? says Mariel Kozberg, a neurobiology MD-PhD candidate and lead author of the paper published in the Proceedings of the National Academy of Sciences. ?By tracking changes in blood-flow control with increasing age, we observed the brain gradually developing its ability to increase local blood flow and, by adulthood, generate a large blood-flow response.?

Hillman says the findings suggest that vascular development may be an important new factor to consider in normal and abnormal brain development.

The team used a unique high-speed, high-resolution imaging approach that takes advantage of the different absorption spectra of deoxygenated and oxygenated hemoglobin in order to determine changes in the concentrations of each.

The researchers found that, with increasing age, there was a gradual development of a localized increase in blood flow, while a strong, delayed decrease in flow was consistently present. Only by adulthood was the positive increase able to balance the decrease in flow.

?Our results suggest that the infant brain might not be able to generate localized blood-flow increases, even if there is neuronal activity occurring, and that the development of blood-flow control occurs in parallel with early neuronal development,? says Kozberg.

?This could suggest that fMRI studies of infants and children may be detecting changes in both vascular and neuronal development?in fact, vascular development may be an important new factor to consider in normal and abnormal brain development.?

The team also found that the younger age groups were highly sensitive to blood pressure increases in response to stimulation and that these increases can cause large increases in blood flow across the brain.

?This finding indicates that the newborn brain is also unable to regulate its overall blood-flow levels,? Kozberg explains. ?This could explain earlier fMRI results in infants and children that were sometimes positive and sometimes negative, because it is difficult to tell whether blood pressure increases are occurring in infants and children. This result suggests that great care should be taken in setting stimulus thresholds in young subjects.?

The researchers add that, since the newborn brain appears to be able to sustain itself without tightly controlled blood flow, their findings suggest that the infant brain may be intrinsically more resistant to damage due to a lack of oxygen than the adult brain.

?This could be an important property to understand, both in terms of understanding how best to treat blood-flow problems in the newborn infant brain, which can cause lifelong problems such as cerebral palsy, and to potentially better understand how to treat the adult brain in conditions such as stroke,? Hillman observes.

This research was supported by grants and student fellowships from the National Institute of Neurological Disorders and Stroke, the National Eye Institute, the National Science Foundation, the National Defense Science and Engineering Graduate Fellowship, the Medical Scientist Training Program, and the Human Frontier Science Program.

Source, Columbia University