The neurophysiological basis of prolonged negative BOLD signals

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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. However, this technique relies on changes in local blood oxygenation rather than measuring the electrical activity in the brain directly. How increases in brain activity results in blood changes has started to be understood, but how and if decreases in activity affect brain blood oxygen is not at all characterised making neuroimaging data very difficult to interpret in terms of decreases in brain activity. Despite this uncertainty, scientists are stating to use FMRI to infer decreases in brain activity and if this inference is correct their studies suggest that the majority of psychiatric (e.g. schizophrenia, major depressive disorder), neuro-developmental (e.g. Autism) neurological (e.g. Alzheimer?s) brain diseases are characterised an inability to ?turn-off? rather ?turn-on? specific brain regions during mental tasks. By directly measuring reductions brain activity, neuroimaging signals and blood oxygen content at the same time we hope to understand the relationships between them and allow this vital aspect of neuroimaging to further our understanding of brain function and its malfunction in disease states.