Neuromagnetic changes of brain rhythm evoked by intravenous olfactory stimulation in humans

To identify the changes in the respective frequency band and brain areas related to olfactory perception, we measured magnetoencephalographic (MEG) signals before and after instilling intravenously thiamine propyl disulfide (TPD) and thiamine tetrahydrofurfuryl disulfide monohydrochloride (TTFD), which evoked a strong and weak sensation of odor, respectively. For the frequency analysis of MEG, a beamformer program, synthetic aperture magnetometry (SAM), was employed and event-related desynchronization (ERD) or synchronization (ERS) was statistically determined. Both strong and weak odors induced ERD in (1) beta band (13-30 Hz) in the right precentral gyrus, and the superior and middle frontal gyri in both hemispheres, (2) low gamma band (30-60 Hz) in the left superior frontal gyrus and superior parietal lobule, and the middle frontal gyrus in both hemispheres, and (3) high gamma band 2 (100-200 Hz) in the right inferior frontal gyrus. TPD induced ERD in the left temporal, parietal and occipital lobes, while TTFD induced ERD in the right temporal, parietal and occipital lobes. The results indicate that physiological functions in several regions in the frontal lobe may change and the strength of the odor may play a different role in each hemisphere during olfactory perception in humans.