Mapping at glomerular resolution: fMRI of rat olfactory bulb

Abstract

The rat olfactory bulb contains ∼2000 functional units called glomeruli which are used to recognize specific characteristics of odorants. Activity localization of individual glomerulae (∼0.002 μL) has important consequences for understanding mechanisms in olfactory information encoding. High‐resolution functional MRI (fMRI) data from the rat olfactory bulb are presented using the blood oxygenation level dependent (BOLD) method at 7 T. Either individual or clusters of fMRI voxels suggestive of activity in the olfactory nerve and glomerular layers were reproducibly detected with repeated 2‐min exposures of iso‐amyl acetate at spatial resolution of 0.001–0.003 μL. The importance of glomerular clustering for olfaction and the implications of BOLD mapping with even higher spatial resolution (i.e., ≪0.001 μL voxels) are discussed. High‐resolution in vivo mapping of the rat olfactory bulb with fMRI at high magnetic field promises to provide novel data for understanding olfaction. Magn Reson Med 48:570–576, 2002.