Magnetoencephalographic (MEG) responses to odor (amyl-acetate) and non-odor stimuli for 1 second were recorded in 9 healthy volunteers (right handed) with a dual 37-channel SQUID (Magnes, Bti Co.) and evaluated by fast Fourier transformation analysis, with the following results: 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 non-odor stimuli. This greater increase 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 density areas at a frequency of 8 Hz were observed over the right hemisphere when no stimuli was compared with non-odor and no stimulus compared with odor. These changes may reflect a high level of vigilance caused by stimulation. 3. When no stimulus was compared with non-odor stimulation, a significant spectral density 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 indicated increased attention in response to random presentation of odor and non-odor. 4. Significant differences at frequencies from 14 to 24 Hz were noted in the contralateral hemisphere when no stimulus was compared with odor stimuli. MEG spectral densities at 21 and 22 Hz were also noted in the contralateral hemisphere when no stimulus was compared with non-odor stimulus. These differences apparently arise from the response of the somato-sensory cortex to non-odor stimuli and amyl-acetate. Alternation of MEG spectral densities at frequencies from 14 to 17 Hz and 23 to 24 Hz in the left hemisphere was noted when no stimulus was compared with non-odor and no stimulus was compared with odor. These results appear to be related to "emotions" of pleasantness and unpleasantness evoked by non-odor and odor.
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