A modular, computer-controlled system for olfactory stimulation in the MRI environment

A multimodal MR-compatible olfactometer with real-time controlling capability

Design of an MR-compatible and computer-controlled odour stimuli system is essential in the studies of human olfactory function. Olfactometers are used to deliver odours to the subjects in an objective manner. We present a portable, computer-controlled eight channels olfactometer able to stimulate olfaction by employing liquid odorant stimuli. We used a high-pressure pump to generate medical grade airflow. After passing through solenoid valve-controlled odour reservoirs, odorant stimulus is conveyed to the nasal mask. The odour delivery delay of the device was measured using photo-ionisation detectors. To assess the application of the designed olfactometer, an fMRI experiment was done with 9 healthy subjects. Two odour stimuli (Vanillin and Rose) were presented to each subject in an alternating block design task of odour and non-odour conditions. The response time of each subject was gathered using the response box. Group analysis revealed a significant BOLD signal change in some regions of olfactory and trigeminal networks including the orbitofrontal cortex, insula, inferior frontal gyrus, hippocampus, cingulate gyrus and piriform cortex. The odour delivery delay measured by photo-ionisation detector was 190 ms, and the subjects' response showed 205 ms for the Vanillin and 243 ms for the Rose odour stimuli. Our portable MR-compatible olfactometer as a stimulation device is capable of creating adequate stimulation suitable for olfactory fMRI experiments.

Improved low-cost, MR-compatible olfactometer to deliver tobacco smoke odor

We describe a low-cost, MRI-compatible olfactometer that delivers fresh cigarette smoke odor, a challenging odorant to present, as well as other odorants. This new olfactometer retains all of the advantages of an earlier design that was capable of only delivering volatile odors (Lowen & Lukas, Behavior Research Methods, 38, 307-313, 2006). The new system incorporates a novel switching mechanism that allows it to deliver fresh smoke generated from a burning cigarette during a stimulus presentation paradigm that might be employed in a cue-reactivity experiment. An evaluation study established that the olfactometer reliably delivered smoke to the participants and that tobacco smoke was discriminated from other odorants; there were no adverse reactions to the device.

An extension of olfactometry methods: An expandable, fully automated, mobile, MRI-compatible olfactometer

BACKGROUND

fMRI experiments on olfaction offer new insights into the complex, but in contrast to other sensory systems, less studied cognition of odors. To perform these experiments is still a challenge.

NEW METHOD

To address the challenge posed by MR settings, an olfactometer design is presented including specific improvements to the limited number of already existing olfactometers. Innovative features such as pneumatically controlled pinch valves, useable in the scanner and providing exact stimulus timing as well as a 3D-printed nasal mask inlet for common sleep laboratory masks that can be used for lateral divided stimulus presentation are introduced. To ensure a fully automated and mobile system, the use of a flexible and easily-adapted Matlab-Code and a portable adaptable container system are presented.

RESULTS

The functional efficiency of these features are proven by results of an fMRI study as well as testing temporal resolution and concentration stability with a mass spectrometer.

COMPARISON WITH EXISTING METHODS

The 24-channel olfactometer design presented here provides an inexpensive alternative to the currently available olfactometers including the achievement of fast onset times, lateral divided stimulus presentation and high flexibility and adaptability to different scientific questions.

CONCLUSION

The olfactometer design presented in this paper can be seen as a realistic and feasible solution to overcome the challenges of presenting olfactory stimuli within the MR setting.

Pulse Width Modulation Applied to Olfactory Stimulation for Intensity Tuning

For most olfactometers described in the literature, adjusting olfactory stimulation intensity involves modifying the dilution of the odorant in a neutral solution (water, mineral, oil, etc.), the dilution of the odorant air in neutral airflow, or the surface of the odorant in contact with airflow. But, for most of these above-mentioned devices, manual intervention is necessary for adjusting concentration. We present in this article a method of controlling odorant concentration via a computer which can be implemented on even the most dynamic olfactometers. We used Pulse Width Modulation (PWM), a technique commonly used in electronic or electrical engineering, and we have applied it to odor delivery. PWM, when applied to odor delivery, comprises an alternative presentation of odorant air and clean air at a high frequency. The cycle period (odor presentation and rest) is 200 ms. In order to modify odorant concentration, the ratio between the odorant period and clean air presentation during a cycle is modified. This ratio is named duty cycle. Gas chromatography measurements show that this method offers a range of mixing factors from 33% to 100% (continuous presentation of odor). Proof of principle is provided via a psychophysical experiment. Three odors (isoamyl acetate, butanol and pyridine) were presented to twenty subjects. Each odor was delivered three times with five values of duty cycles. After each stimulation, the subjects were asked to estimate the intensity of the stimulus on a 10 point scale, ranging from 0 (undetectable) to 9 (very strong). Results show a main effect of the duty cycles on the intensity ratings for all tested odors.

An fMRI study on the influence of sommeliers' expertise on the integration of flavor

Flavors guide consumers' choice of foodstuffs, preferring those that they like and meet their needs, and dismissing those for which they have a conditioned aversion. Flavor affects the learning and consumption of foods and drinks; what is already well-known is favored and what is new is apprehended. The flavor of foodstuffs is also crucial in explaining some eating behaviors such as overconsumption. The "blind" taste test of wine is a good model for assessing the ability of people to convert mouth feelings into flavor. To determine the relative importance of memory and sensory capabilities, we present the results of an fMRI neuro-imaging study involving 10 experts and 10 matched control subjects using wine as a stimulus in a blind taste test, focusing primarily on the assessment of flavor integration. The results revealed activations in the brain areas involved in sensory integration, both in experts and control subjects (insula, frontal operculum, orbitofrontal cortex, amygdala). However, experts were mainly characterized by a more immediate and targeted sensory reaction to wine stimulation with an economic mechanism reducing effort than control subjects. Wine experts showed brainstem and left-hemispheric activations in the hippocampal and parahippocampal formations and the temporal pole, whereas control subjects showed activations in different associative cortices, predominantly in the right hemisphere. These results also confirm that wine experts work simultaneously on sensory quality assessment and on label recognition of wine.