Revealing Columnar Architectures Using fMRI: Challenges and Possibilities

Abstract

Among the many neuroimaging tools available for studying human brain functions, functional magnetic resonance imaging (fMRI) is the most widely used today. One advantage of fMRI over other imaging techniques is its relatively high spatial resolution. High-resolution fMRI, with its superb signal-to-noise ratio and improved tissue-vessel specificity, has strengthened the capability of fMRI and allowed mapping of fine cortical architectures in the human brain. In this presentation, I will first explain the factors limiting the spatial specificity of the blood oxygenation level-dependent (BOLD) effect, based on which most of fMRI experiments are conducted, and the measures dealing with these factors. I will then introduce several highresolution (sub-millimeter) studies on the functional organization of human primary visual cortex (V1), including mapping of ocular dominance columns, mapping of temporal frequency dependent domains and direct demonstration of tuning to stimulus orientation. Finally, I will present some recent results from highresolution studies revealing orientation specific responses in large draining veins, a finding closely related to the interpretation as why conventional low-resolution (～3mm) fMRI signals can be reliably used to decode stimulus orientations.