Localized cerebral blood flow response at submillimeter columnar resolution

Functional magnetic resonance imaging (fMRI) has been widely used for imagi ng brain functions. However, the extent of the fMRI hemodynamic response ar ound the active sites, at submillimeter resolution, remains poorly understo od and controversial. With the use of perfusion-based fMRI, we evaluated th e hemodynamic response in the cat visual cortex after orientation-specific stimuli. Activation maps obtained by using cerebral blood flow fMRI measure ments were predominantly devoid of large draining vein contamination and re producible at columnar resolution. Stimulus-specific cerebral blood flow re sponses were spatially localized to individual cortical columns, and column ar layouts were resolved. The periodic spacing of orientation columnar stru ctures was estimated to be 1.1 +/- 0.2 mm (n = 14 orientations, five animal s), consistent with previous findings. The estimated cerebral blood flow re sponse at full width at half-maximum was 470 mum under single-stimulus cond itions without differential subtraction. These results suggest that hemodyn amic-based fMRI can indeed be used to map individual functional columns if large-vessel contributions can be minimized or eliminated.