Tim Jacob - Smell Research
The same happens for the putative human signalling compound androstadienone. Additionally, as the exposure-induced sensitization occurs, there is a change in the perceptual quality of the odour; from no smell, to sweet/honey/minty, to urinous/sweaty.
vs. bad smells.
Bad smells are warning signals and need
to be responded to quickly. We have measured reaction times to good and
bad smell and found that, indeed, we react quicker to bad smells (at equal
of psychological and physiological responses to olfactory stimulation.
Olfactory Event-Related Potentials (OERPs) were recorded by EEG using monopolar electrodes located at Fz , Cz , Pz, T3, C3, C4, T4 electrode sites (International 10/20 System) in 28 young students (range 18-25 years ). Brain potentials were amplified and digitised and an average was created for all subjects for 20 trials, while the subjects concentrated on a visual task. Pulses of amyl acetate (saturated vapour) were mixed 1:3 with medical air for 35, 50, 75, 100 and 200ms duration and delivered at 2.5, 5,10 and 60s inter-stimulus intervals (ISI) respectively. In each condition, the odour was delivered between 5 to 15 times. Each session was separated by a 2 min break to relieve fatigue and allow for neuronal recovery. Airflow, temperature and humidity were kept constant. The amplitude of the OERP was measured as the difference between the negative and positive peaks (sometimes referred to as N1-P2 or N1-P3). For the psychometric test the subjects were given the same stimulus protocol. A number of pulses, between 15-25, were delivered and they were asked to record how many they detected.
There was a decline in the number of odour pulses detected both with decreasing stimulus and ISI. In the matching set of physiological experiments there was also a decline in the OERP when either odour concentration or ISI were decreased. The decline in perception as ISI decreases probably results from the process of adaptation occurring in the olfactory receptor neurones, although there may also be a contribution from central habituation, and this is reflected in the decreased OERP amplitude. The increased amplitude of the OERP with increasing stimulus strength results in increased perception once the stimulus has achieved a threshold value. Perceptual and physiological thresholds were similar.
We are investigating the effects of certain odours on the following physiological parameters:
Smell has the ability to affect our physiological and psychological state via two mechanisms; (1) the instrinsic pharmacological properties of the odour molecule itself and (2) contextual association and memory. This latter has been extended to conditioned reflexes in animals.
We respond differently to different smells. While the biological significance of malodours is clear, the reason for the existence of pleasant odours is less obvious. Can we observe differences in our psychophysiological response to malodours and pleasant smells?
To detect and measure anosmia (loss of
smell), to help people who have lost their sense of smell, or to evaluate
treatments to cure anosmia, we need to be able to measure the activity
of the olfactory system. At present this is difficult. To measure it requires
the recording of electrical activity in response to a stimulus (smell)
by placing wire electrodes far up the nose. Current methods are invasive
and uncomfortable at best.
We hope to be able to investigate:
The characteristics of the psychological perception of the malodours butyric acid and n-valeric acid were studied by olfactometry. The odours were delivered to the nostrils via a teflon canula in a continuous air-stream with a total flow rate of 3 L/min. The duration of a random number of odour pulses was set by computer-controlled solenoid valves to last for 35, 50, 75, 100 and 200 ms with inter-stimulus intervals of 2.5, 5, 10 or 60 s. Subjects were required to indicate the number of pulses they could detect. The results showed that the number of odour pulses detected increased with increasing the pulse duration or inter-stimulus interval. 3D curve fitting with an exponential function revealed that the perception of odour (the percentage of odour pulses detected) was positively correlated to the concentration (pulse duration) and the inter-stimulus interval in both odours tested. However, more interesting phenomenon were revealed by analysing the data in terms of gender. The perception of n-valeric acid was different between male and female subjects. The perception was correlated both to the concentration of the odour and the inter-stimulus interval in male subjects, while it was only correlated to the inter-stimulus interval in females. As for butyric acid, there was no significant gender difference in the correlation of perception with the concentration and inter-stimulus interval. Furthermore, the threshold of the perception of both odours was higher in male than in female subjects. The results suggest that there are different perceptual models for different odours and that, for certain malodours, women are more sensitive than men.
published in Chemical Senses 26(6), 789: (2001)
The electro-olfactogram (EOG) is considered
to be the summated generator potential of olfactory receptor cells and
therefore represents peripheral olfactory events. Recording of human EOG
is technically difficult due to poor access to the olfactory mucosa and
the nasal irritation is tolerated by few subjects. The evoked potentials
at recorded on either side of the bridge of the nose in response to two
odorants, n-amyl acetate and benzaldehyde, were recorded simultaneously
with the EOG, recorded conventionally with an intranasal electrode, and
the olfactory event-related potential (OERP) recorded using scalp electrodes.
Significance This non-invasive method of recording the EOG will have benefits for the objective assessment of olfactory function.