Introduction Psychophysical studies and our daily experience have shown that when we are hungry,food smells stronger and more pleasant[1].After we are full,the same dish smells weaker and less pleasant.Which olfactory stages are involved in these changes,and what are the mechanisms? The studies on the relation between olfaction and feeding almost exclusively focus on higher levels of the olfactory pathway,that is,the olfactory and the orbitofrontal cortexes.However,investigations at the level of the olfactory bulb (OB),the first information coding and processing center in the brain,is very scarce[2,3].The peripheral sensory information flows to higher centers it is critical for the interpretation of higher level cortical and cognitive processing to characterize fully the same types of modulation that may occur in the earlier stages.We have used high-resolution functional MRI (fMRI),in vivo and ex vivo magnetic resonance spectrometry (MRS),and physiological recording to analyze the effects of feeding on the neuronal responses,the neurotransmission dynamics,energy metabolism,electrical firing,and the relationship among these parameters.