Topographical EEG maps of human responses to odors

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Abstract
The physiological response to seven odors (birch tar, galbanum, heliotropine, jasmine, lavender, lemon and peppermint) was assessed by EEG recordings from 19 scalp loci from 16 young adult females. Topographic maps were constructed from the amplitude spectra in four frequency bands: delta (1–4 Hz), theta (4–8 Hz), alpha (8–13 Hz) and beta (13–30 Hz). Eight seconds of representative and artifact-free EEG were selected for FFT analysis before onset of odor delivery, and at three times after stimulus onset. EEG was also quantified at 30 s after stimulus termination. Subjects differed in their subjective responses to the odors, with the most consistently arousing and strong odors being galbanum, lavender, lemon and peppermint. Heliotropine was notably weak. The most pleasant odors were lemon and peppermint, while birch tar, galbanum and lavender were consistently unpleasant. EEG map changes occurred in one or more frequency bands in each subject in response to one or more of the odors. EEG map changes sometimes occurred even with weak odors and even when the subject seemed unaware of the odor's presence. This was most notable with heliotropine. Across subjects, the most consistent responses to odors were in the theta band. Analysis of variance confirmed that certain odors caused statistically significant theta increases over the left anterior group of electrodes. Both right hemisphere groups tended to have significant theta increases. The odors that caused the greatest increase in theta were birch tar, jasmine, lavender and lemon. On the other hand, during blank control trials, theta activity diminished. There was also a significant odor by epoch interaction over the right posterior set of electrodes. Several of the odors caused increased theta at one or more epochs. Lemon caused an immediate increase in theta that abated with time. Birch tar induced a delayed response that persisted after the stimulus was turned off. Jasmine and lavender tended to induce theta sooner than birch tar, but the effect did not outlast the stimulus. Increased theta was not associated with EEG signs of drowsiness. We conclude that all odors affected the EEG in at least some subjects, and all subjects responded to at least some odors. Widespread increase in theta occurred in most subjects during stimulation with such odors as birch tar, jasmine, lavender and lemon.

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