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Who knows what there is to know about the nose?

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Who knows what there is to know about the nose?

Asked by Charli Tricase of Amherst, Massachusetts, USA

Does your nose smell what your eyes see?

Research suggests that the nose does indeed smell what the eyes see. The human sense of smell is unreliable acting by itself. It needs visual cues to be more accurate.

The underlying brain network involved in this olfactory (smell) and visual (sight) process has been studied by two London researchers. They administered a number of tests to subjects where the researchers watched the brain activity of subjects on an MRI as they perceived smell and sight stimuli. The researchers manipulated the stimuli in various combinations and watched the brain changes in subjects as they did so.

The researchers, Drs J A Gottfried and R J Dolan of the Functional Imaging Laboratory of the Wellcome Department of Imaging Neuroscience, found that visual cues impact upon the olfactory cues as registered in the frontal part of the brain's hippocampus and the brain's rostromedial orbitofrontal cortex. They report their findings in the July 2003 issue of Neuron.

Does the colour of something affect how you smell it?

Colour has a profound effect on the perception of smells. For example, strawberry-flavored drinks are judged to smell more pleasant when coloured red than when coloured green. And descriptions of the "nose" of a wine are dramatically influenced by its colour.

This is according to six researchers from the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain at Oxford University. Dr R A Osterbauer and colleagues report in the June 2005 issue of the Journal of Neurophysiology on their experiments with MRI technology.

Colour cues affect olfaction as seen by the changes in brain activity in the brain's caudal regions of the orbitofrontal cortex. In their experiments, laboratory subjects were given various combinations of smells - lemon, strawberry, spearmint, or caramel - and colours - yellow, red, turquoise, or brown.

When a colour and smell matched expectations, such as yellow colour together with a lemon odour, there was more activity in brain regions that process olfactory information than when the smell was given alone. Mismatches of colour and smell produced less brain activity.

Thus, actions such as adding red colouring to white wine can alter how a person perceives the wine's odour - and we can watch the brain doing this.

Does mood affect your ability to smell?

French scientists have found that your mood does indeed affect your ability to smell. In their study of depression-prone people, they discovered that depressives have a poorer smell sensitivity, a poorer ability to detect smells, and a greater tendency to over-estimate the pleasantness of smells.

The French researchers also showed that alcoholic, drug-addicted, and anorexic people have impairments in their sense of smell. Dr S Lombion-Pouthier and colleagues from the Laboratoire de Neurosciences at the Universite de Franche-Comte in Cedex, France present their findings in the February 2006 issue of the Journal of Affective Disorders.

Does smoking affect your ability to smell?

Japanese scientists discovered the extent of smoking affecting one's ability to smell when they studied patients who had undergone surgery for sinus problems.

The researchers from the Nagoya City University Medical School found that smoking induced hyposmia (loss of the ability to smell) was more pronounced in patients who had been smoking for many years. In general, the greater the number of years of smoking, the greater the loss of smell. Dr K Sugiyama and five colleagues report their findings in the September-October 2006 American Journal of Rhinology.

Why doesn't the smell of my babies dirty nappy bother me?

Studies show that mothers are consistently less disgusted by the smell of their own baby's dirty nappy compared to the smell of the dirty nappies of other babies.

In a study by Dr Betty Repacholi of the Department of Psychology at the University of Washington in Seattle (to be published in the Journal of Evolution and Human Behaviour, mothers were given pairs of unlabelled nappies to smell. Some were from their own baby, others were from the babies of someone else. The mothers consistently judged the smell of their own baby's faeces as "less revolting".

Why does nature seem to build this "less revolting" mechanism into mothers? Mothers may merely become used to the smell of their own child's faeces. Or they may be picking up some olfactory cue of relatedness that we still do not entirely understand. But something more profound may be occurring too.

According to Drs V Curtis, R Aunger, and T Rabie of the London School of Hygiene and Tropical Medicine, disgust is a powerful human emotion that has been little studied until recently. They argue in the 7 May 2004 Proceedings of the Royal Society of London, Series B, Biologicl Sciences that "the human disgust emotion may be an evolved response to objects in the environment that represent threats of infectious disease".

So if disgust emerged as an emotion to keep us from getting close to unhygienic, rotten, or potentially dangerous substances, being disgusted by the body products of our own babies would probably not help our species survival at all.

Why does garlic make your breath smell bad, but other vegetables don't?

Unlike other vegetables, garlic has a powerful antibiotic and antifungal compound call allicin. Allicin has some medicinal purposes and can even be used in treatments for such conditions as hardening of the arteries (arteriosclerosis) and obesity. Allicin dissolves fats and is an antioxidant.

Garlic has been used as a folk herbal remedy for centuries. According to Dr D M Bautista and eight colleagues from the Department of Cellular and Molecular Pharmacology at the University of California at San Francisco, writing in the August 2005 Proceedings of the National Academy of Sciences of the United States of America, "the molecular mechanisms underlying these effects [of garlic] remain unknown".

Interestingly, allicin is not in garlic in its natural state. Allicin is produced only when the garlic clove is damaged such as through chopping or chewing. When damage occurs to the clove, alliinase and alliin, two chemicals existing in the undamaged garlic, act upon each other to create allicin.

Garlic belongs to the Alliium family of plants that produce organosulfur compounds. Allicin is one of these. It is very pungent, hence "garlic breath" when eaten.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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