Webinar on Brain Imaging

Functional magnetic resonance imaging (fMRI) measures brain activity via the accompanying changes in blood flow, volume, and oxygenation. As an indirect measure, the accuracy of fMRI is contingent on how closely the measured hemodynamic signals map onto the underlying neuronal activation patterns. The most specific hemodynamic signals arise from the capillary bed, the smallest vessels within gray matter (<20um) that directly serve active neuronal sites. At clinical field strengths, signals from larger veins at the surface of gray matter typically hinder the accuracy of fMRI. 7T allows for improved accuracy in two ways; first, signals from capillaries are enhanced while those from larger veins are reduced. Second, the high signal-to-noise allows for high spatial resolutions that can be exploited to pinpoint the vascular origin of signals measured according to physical location. This talk will give a view into how these advantages translate to increased fMRI specificity to neuronal activation patterns, in light of the correspondence of 7T BOLD fMRI to neuronal activity measured with intracranial electrophysiology (ECoG), in humans. An overview of how the improvements in specificity are being used to measure activity in small neuronal populations, at the spatial scale of columns and layers, will be presented.