IntroductionBrain activation in response to olfactory stimuli has been studied using functional magnetic resonance imaging (fMRI), but there is little knowledge about processing repeated olfactory information which is usual in daily life.MethodsThis fMRI study was designed to investigate brain response to repeated odorant stimulation with positive and negative valences in 12 healthy right-handed volunteers. There was a 25-min rest interval between two fMRI runs with identical stimulation paradigms with two odors, as phenylethyl alcohol (PEA) and isovaleric acid (IVA), and the two odors were released alternately.ResultsThere was a similar activation pattern in regions of primary and secondary olfactory cortex induced by odors of both valences, especially by negative odor. Weakened activation of the brain is responsive to repeated both pleasant and unpleasant smell. Nevertheless, the repeated unpleasant odor has a more intimate relationship with the piriform cortex, amygdala, and hippocampus.ConclusionWe conclude that asymmetric brain activation in response to repeated odorant stimulation depended on valences and that the unpleasant odor can evoke more negative emotion and profound memory.ImplicationsWe explore the central processing about repeated olfactory information applied fMRI for the first time, revealing asymmetric brain activation in response to repeated odors of pleasantness and unpleasantness.