Coherence analysis of EEG changes during odour stimulation in humans

In a pilot study, EEG changes during odour administration were evaluated by coherence analysis. Ten normal adults were studied. Simultaneous recordings of 16 EEG channels with, and without, odour administration were stored on magnetic tape for further processing. EEG signals were analysed using a signal analyser. Coherence spectra were calculated between all possible channel pairs on the scalp. The amount of data was reduced by extracting broad band coherence values for five frequency bands: delta (2-3.9 Hz), theta (4-7.9 Hz), alpha 1 (8-9.9 Hz), alpha 2 (10-12.9 Hz), and beta 1 (13-17.9 Hz). Coherence values extracted from the control EEG recordings and those during odour administration were compared to evaluate the presence of any significant differences. The results demonstrated significant changes in the EEG coherence between the two control recordings (control before and control after) in the theta and beta 1 bands. These frequency bands were therefore excluded from the examination. During odorant stimulation with methyl-cyclopentenolone, the coherence in the delta band decreased in the frontal region, while that in the alpha 1 and alpha 2 bands increased in the temporal region. During odorant stimulation with scatol, the coherence in the delta band decreased in the frontal region, while that in the alpha 1 and alpha 2 bands increased between the longitudinal electrode locations. It was suggested that EEG coherence mapping may provide the basis for the development of an objective test of olfactory function in humans.