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Olfactory research methods

There are many new and developing methods for researching the effects of fragrance on people, both physiological and phsychological. Below is a selection of research methods used by olfactory scientists to assess the benfits fragrance can bring to peoples everyday lives.


	Brain Electrical Activity Measurements

Impressive progress has been made during the last two decades in developing objective, reliable and reproducible test methodologies for measuring brain response to olfactive stimuli. Major contributions have come from renowned researchers in the USA, Europe and Japan. Work conducted by Lorig and his team at Washington and Lee University, USA, Kobal and others at the University of Erlangen, Germany and Torii as well as Saito in Japan can be considered as ground breaking achievements.

In addition R&D efforts in many major fragrance companies were directed at research on fragrance benefits using modern instrumentation in the field of Electroencephalography (EEG) and functional Magnetic Resonance Imaging (MRI). These findings are often treated as trade secrets or are protected through patents. Also worth noting is the support and contribution made by Sense of Smell Institute (Fragrance foundation) in encouraging younger researchers to get involved in olfactory research using robust methodologies for scientific validation.


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	Contingent Negative Variation (CNV)

Researchers such as Torii et al have conducted some pioneering research in the use of CNV to measure stimulation and relaxation properties of fragrance materials. They concluded that Jasmin odor causes a significant increase in the CNV measured at frontal and left central sides of the cortex (stimulation), while Lavender causes a significant decrease (relaxation). Work of Lorig and Roberts and Saito also sheds light on the use of CNV measurement in the evaluation of brain response to fragrance materials.


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	Functional MRI

EEG is very fast and shows the global activity of a large number of cortical neurons. It is fast but gives very little idea of which brain structures are involved. On the other hand, fMRI is a powerful way of imaging brain activity and can localize which structures are involved very precisely. However, it is relatively slow and costly.

The use of fMRI in olfactory research has increased considerably during the last ten years or so. A number of publications outline their findings, especially in exploring the relaxing and invigorating aspects of perfumes. The technique is getting attention from both academic and industrial researchers.


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	Systolic Blood Pressure

Certain fragrance materials have been found to reduce the rise in blood pressure under stressful conditions. A patent discloses that the use of nutmeg oil and neroli oil in fragrances has a blood pressure reducing effect. Nagai et al from Japan have published their results suggesting that some of the odorants tested were able to reduce the blood pressure of subjects by as much as 24%.


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	Electro-Dermal Activity (EDA)

It is stated that the steady current between two points at the skin surface is increased as a result of arousal. Various researchers used skin conductance changes in response to fragrance materials to measure the degree of arousal or if an increase in vigilance during a task.


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	Startle-probe reflex

Ehrlichman and co-workers used this technique to probe subject responses to pleasant odor, unpleasant odor and no-odor conditions. Generally, the startle reflex is enhanced when the organism is in a negative affective state and reduced when the organism is in a positive affective state. Researchers observed that the reflex under unpleasant odors was significantly enhanced compared with no-odor state, and marginally enhanced compared to the pleasant odor condition. The difference between the pleasant and no-odor condition was not significant.

It was postulated that unpleasant odors by themselves are enough to generate a negative affective state, but the generation of positive affective state by pleasant odors depends on having an appropriate context. Putting it differently, it is possible that all odors tend to enhance the reflex through enhanced arousal. In the case of unpleasant odors, the effects of arousal and the negative emotional state are additive; in the case of the pleasant odors, the arousal and the effective component counteract each other. In any case the methodology provides reproducible measurements under test.


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	Pupil dilation/constriction

The technique is used by a number of researchers to measure pupil dilation in response to the presented odor stimuli with the help of an infrared television camera. Some of the odorants tested were rosemary oil, bromostyrol, tuberose and banana. The findings suggested that all stimuli elicited pupil enlargement, response magnitude of good intra-individual reproducibility, but the pupil enlargement generally was less at the second presentation of the stimuli, suggesting diminished attention.


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	Evoked Potentials

An Evoked Potential is an electrical potential recorded from a human or animal following the presentation of a stimulus such as an odor. These responses are distinct from spontaneous potentials such as EEG. Evoked Potential amplitudes tend to be low and are recorded from central nervous system structures and are considered to be more closely associated with an unadulterated response to stimuli.

Research conducted by Kobal and co-workers on olfactory Evoked Potential activity and hedonics revealed some interesting insights. They found that pleasant emotions are largely processed by the left hemisphere and unpleasant emotions more often by the right one. They found that hedonic response occurred in very early phases of the olfactory evoked response and prior to the onset of cognitive process. They also concluded that the coding of hedonic quality is not learned or conditioned but innate and hard wired. These findings were in accord with earlier works of Ehrlichman and Saito.


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	Electroencephalography (EEG)

Evoked Potentials and CNV are aspects of an immediate response of the brain to odors while continuous EEG recordings look at the global changes in brain wave activity in response to a longer term odor exposure. One of the brain waves measured by EEG is called the “alpha wave”. It has a particular frequency of 8-12 Hz or waves per second. Increased alpha-wave activity in the brain is a sign of relaxation. A number of researchers have studied the effect of odorants on brain wave activity. It was suggested that lavender, cineol, sandalwood and a-pinene increase alpha wave activity (relaxation) whereas jasmin increased beta wave activity (arousal). Lorig et al reported slow EEG activity with spiced-apple odor compared to lavender and eucalyptus odors. EEG measurements have been used by the industry to validate claims for fragrances that relax the user. The trend is growing.


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	Physiological Measurements

Techniques and measurements such as evoked potential, CNV and EEG have helped to evaluate fragrance materials scientifically for their effect and benefits. Such effects have also been validated by the use of a number of physiological parameters.


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	Heart Rate

Kikuchi et al and Nagai in separate studies found that the presentation of lemon odor and sweet fennel odor lowered heart rate signalling increasing alertness. Rose odor did the opposite. Furthermore, Oguri and co-workers used heart rate measurements to establish that pleasant odors activating the central nervous system increase the heart rate variations while sedate odors decrease them. Hanisch used heart rate as a measure of fear and found that the pleasant effect of fragrances reduced fear.


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	Microvibration

A technique for studying psycho-physiological changes mediated by fragrances. It involves measuring a fine tremor induced by muscle tension in response to a stimulus. According to Sugano and Sato, Lavender decreases microvibration frequency/amplitude, indicating relaxation. Jasmin, Camomile and Musk odor increase these parameters.


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	Cortisol levels

Measuring cortisol levels as an indication of fragrance benefit in relaxation etc. has been developed and used by researchers in recent years. United States patent US 6830755 issued to J&J relates to a method of formulating personal care products with relaxing fragrances that are effective in reducing cortisol levels and/or increasing slgA levels. The Cortisol level as an indicator of sexual arousal in women exposed to androstadienone odor was reported by Wyart and Sobel in their paper in Journal of Neuroscience, Feb. 7, 2007, 27(6), 1261-1265.


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