Coherence analysis of EEG changes during olfactory stimulation.

In a pilot study, EEG changes during odor stimulation were evaluated by coherence analysis. Ten normal adults were studied. Simultaneous recordings of 16 EEG channels with and without odor stimulation were stored on magnetic tape for further processing. EEG signals were analyzed using a signal analyzer. 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 odor stimulation were compared to evaluate the presence of any significant differences. The results demonstrated significant changes in the EEG coherence between the two control recordings (before and 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 bilateral 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 in the frontal, temporal and occipital regions. It is suggested that EEG coherence mapping may provide the basis for the development of an objective test of olfactory function in humans.