Functional MRI of regional brain responses to 'pleasant' and 'unpleasant' odors.

Conclusions: Our findings demonstrate that functional MRI (fMRI) combined with a questionnaire is a useful method for studying the neuroanatomy of olfaction. Further studies with various odorants and questionnaires would provide an even better understanding of the mechanism of olfactory perception.

Objectives: To better understand the mechanism of odorant perception in the central nervous system.

Subjects and methods: fMRI was used to identify the activated regions during stimulation by two odorants, beta-phenyl ethyl alcohol and gamma-undecalactone. Participants were asked to describe the quality of the odor and to rate odor intensity and odor hedonic valence. Activation at each region was statistically analyzed according to the answers.

Results: The bilateral middle orbitofrontal cortex (OFC), left lateral OFC, right insula, and bilateral anterior/middle cingulate gyri were most frequently activated by odor stimulation. Left middle OFC was significantly more often activated in the participants who could not identify the odor correctly (p = 0.016). The left middle OFC and right lateral OFC were significantly more often activated in the participants who perceived the odor stimulation as unpleasant (p = 0.03), while the right anterior cingulate gyrus was more often activated in those who perceived the odor as pleasant (p = 0.03).