Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, PC23
Human olfactory gamma oscillations; correlation with the respiratory cycle.
T. Jacob1, H. Gunney1
1. School of Biosciences, Cardiff University, Cardiff, United Kingdom.
Odour-induced olfactory bulb oscillations, called “reactions” by Adrian (1942), were first recorded in the hedgehog in response to clove oil and asafoetida. He reported that an intense stimulus produced a continuous series of small irregular waves with a frequency of 50 Hz. More recently, gamma oscillations (40-100Hz) have been shown to be evoked by olfactory stimulation, particularly during a discrimination task, in mice and rats and are initiated during the inspiratory phase of the respiratory cycle (see review by Kay et al., 2009). In humans, intravenous olfactory stimulation with alinamin has been found to evoke gamma band oscillations at the frontal scalp (Ishimaru et al., 2002). Here, we intended to investigate the presence and nature of gamma oscillations originating in the human olfactory bulb, as well as the influence of the respiratory cycle on these oscillations during periods of odour stimulation. Consenting volunteers were exposed to an odour (vanillin or butyric acid) on a scent card held about 20mm from the nostrils, while we simultaneously recorded the electrical activity at various scalp positions, including N1 (a site at the bridge of nose between the nasion and the medial canthus), using electroencephalography (EEG). Odour stimulation was found to significantly increase the power of gamma-band oscillations at N1 compared to control breathing (t-test, p=0.004). During odour stimulation, respiratory phase was found to have a significant effect on gamma power at N1 (one-way repeated measures ANOVA, F(1.6,9.7)=7.901, p=.012; power =.823 at 0.05 significance level). Post hoc analysis showed that gamma power increased significantly in the inspiratory phase upon odour stimulation (LSD (least significant difference), p=0.030), whereas gamma power in the expiratory phase of respiration showed no significant difference upon odour stimulation. This study demonstrates that olfactory induced gamma oscillations can be recorded on the surface of the scalp in humans and we suggest that the observed increase in gamma power in the inspiratory phase reflects odour processing by the olfactory bulb.
Where applicable, experiments conform with Society ethical requirements