Magnetoencephalographic Responses to Odor and Air by Fast Fourier Transformation Analysis in Human

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Magnetoencephalographic (MEG) responses to odor (amyl-acetate) and air stimuli for 1 second were recorded in humans with a 74-chennel SQUID system (MagnesィイD1TMィエD1, Bti Co.) and evaluated by fast Fourier transformation analysis. The following were obtained :1. On MEG analysis, the spectral density increase in the left mid-central region at a frequency of 7 Hz was significantly greater in response to odor than in response to air stimuli. This greater increase in response to odor is apparently related to the presence of the odor perception mechanism in the orbital frontal area, a major center of the olfactory system.2. Both increased and decreased spectral areas at a frequency of 8 Hz were observed over the right hemisphere when no stimulus was compared with air and no stimulus was compared with odor. The changes may reflect a high level of vigilance caused by stimulation.3. When no stimulus was compared with air stimulation, a significant spectral increase at a frequency of 11 Hz was noted. Similar trends were observed at frequencies of 11 and 12 Hz when no stimulus was compared with odor. These findings an increased level of attention in response to random presentation of odor and air.4. Significant differences at frequencies of 21 and 22 Hz were noted in the contralateral hemisphere when no stimulus was compared with air and no stimulus was compared with odor. These differences apparently arise the responses of the somato-sensory cortex to air and odor.5. Alternation of MEG spectral densities at frequencies from 14 to 17 Hz and from 23 to 14 Hz in the left hemisphere was noted when no stimulus was compared with air and no stimulus was compared with odor. These results appear to be related to the "emotions" of pleasantness and unpleasantness evoked by air and odor.