Submillimeter functional localization in human striate cortex using BOLD contrast at 4 tesla: Implications for the vascular point-spread function

Using multislice segmented echoplanar imaging at 4 T, we have measured an u pper bound to the cortical vasculature point-spread function (PSF) using fu nctional magnetic resonance imaging (fMRI) in humans. Our experiments demon strate that cortical subunits that are approximately 700 mu m apart can be resolved using the early part of the hyperoxygenation phase of the blood ox ygenation level-dependent (BOLD) effect. This was accomplished using brief (4 sec) single trials of monocular and binocular stimulation of ocular domi nance columns in human primary visual cortex. The data suggest that at even higher magnetic fields, the cortical vasculature PSF may be limited by the extent and nature of horizontal connections and not signal-to-noise ratio. (C) 1999 Wiley-Liss, Inc.