Mapping at glomerular resolution: fMRI of rat olfactory bulb.

The rat olfactory bulb contains approximately 2000 functional units called glomeruli which are used to recognize specific characteristics of odorants. Activity localization of individual glomerulae ( approximately 0.002 microL) 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 microL. The importance of glomerular clustering for olfaction and the implications of BOLD mapping with even higher spatial resolution (i.e., <<0.001 microL 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.