GLM and second-level analysis showing activated voxels during patterned stimulation of the olfactory bulb that correspond to regions of the olfactory system and associated brain regions. (A–C) The 3D activation map depicts results of general linear model (GLM) analysis to detect all significantly activated voxels (increase in activation: orange; decrease in activation: blue) during application of (A) 20 Hz and (B) 100 Hz stimulation to the olfactory bulb. (C) A second-level analysis (difference) was performed to map significantly different BOLD responses between the two stimulation protocols (orange: significantly stronger activation with 100 Hz stimulation; blue: significantly stronger activation with 20 Hz stimulation). BOLD responses of the left AON and areas of the right piriform cortex are significantly stronger during 100 Hz, compared with 20 Hz, stimulation applied to the olfactory bulb. VOIs that showed a significant difference between stimulation protocols in the VOI analysis (see Figs 3–6) are labeled and marked by an outline to depict an overlap between VOI analysis and the second-level analysis. All other analyzed VOIs (volumes of interest) are displayed in a transparent manner.