Ever had a cold hijack your sense of smell? Some people's sense of smell gets a lot more twisted than that. Find out what the world is like when a banana smells like rotten meat, and roses smell like garbage.
When we look at a banana we know that we're seeing thousands of little particles of light, in many subtly-different combinations, and our brain is constructing those pieces into an identifiable object. When we smell a banana, we perceive it as one smell, like a matte sheet of color. That is until we get troposmia — literally a twisted sense of smell.
Getting a cold gives us a slight sense of what troposmia is like. Familiar smells flatten and distort themselves, so that fruit stops smelling sweet like sugar, and starts smelling sweet like decay, and bread has a kind of papery smell, without its usual richness. We smell with a combination of receptors; some in our nose, and some in the tissue between the nose and the roof of the mouth. Getting sick plugs up most of the receptors in the nose and distorts the way we usually smell things. Suddenly we realize that what we thought of as "banana smell" was actually a complicated group of chemicals, hitting our smell receptors at two different sites in a very particular way. The scent "picture" of a banana is as intricate as the sight of a banana. We just didn't know it.
Troposmia, a more lasting (and mysterious) twisting of the sense of smell, puts some sensors out of commission, and amps up the signal on others. People with troposmia could smell one component of the sweetness of flowers, but not the accompanying scents, and so the flowers would smell like chemicals. Other scents, like paper or metal, may not be distorted at all. It all depends on which bits of the nervous system are working. Troposmic patients tend to be able to roughly "place" smells, but are unable to specifically identify them. When they go to doctors to be treated, and are presented with different smells, they may be able to say something smells "outdoorsy" or "like it belongs in a kitchen," but are unable to pin down a scent. (Otolaryngologists have entire books of scratch n' sniff pages for patients to try. Now I know what I want for Christmas.)
There is evidence that troposmia originates in the nose. People with troposmia often have reduced numbers of smell receptors in their nose and mouth. They also tend to have a large ratio of immature to mature neurons. When doctors anesthetized the neurons, the strange smells went away. The again, some people with twisted senses of smell showed increased neural activity in regions of the brain dealing with smell. Their noses were fine, but their brains perceived new and different scents anyway.
There is some hope for people who suddenly have their sense of smell completely rearranged. Sufferers of troposmia say it's at its worst in the early days. Eventually some of them adapt, and come to understand and even appreciate a new sense of smell. There's also an extremely odd condition called euosmia. Consider the letters "euosmia" shares with "euphoria," and take a guess at what that is. Following a severe infection, one woman believed that everything smelled delightful — though hopefully not delicious.
What's is your worst tale of twisted smell?
[Via Distortion of Olfactory Perception, Euosmia: A Rare Form of Parosmia]