The neurophysiological basis of spontaneous fluctuations in neuroimaging signals

A technique called blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) can determine levels of different activity in parts of the living human brain and how malfunctions can occur in disease. Furthermore, this technique has been extended to look at communication between brain regions based on the similarity between ongoing signals (‘brain waves’) in connected parts of the brain. However, these magnetic techniques are based on changes in the oxygen content of the blood rather than direct measures of brain activity. They are used because changes in oxygen content can be observed without performing surgery on the brain in human subjects. There is concern, however, because the manifestation of these ongoing brain waves in blood oxygen content is poorly understood and as such the validity of using them to infer communication between brain structures has been questioned. By directly measuring spontaneous brain activity, neuroimaging signals and blood oxygen content at the same time the proposed research hopes to understand the relationships between them and allow this potentially important aspect of neuroimaging to further our understanding of brain function.