At a symposium on gastro-psychology during this year's Association for Psychological Science convention, Rozin pointed out that humans are the only species — we know about — that specifically seek out what would otherwise be considered negative events. Healthy, sane humans do not stab themselves in the thighs, or bathe their eyes in lemon juice. So why do we so love to assault one of the most sensitive organs in the human body, the tongue, with what amounts to chemical warfare?
Chillies are unique among foods that we should otherwise not enjoy. For example, humans also have natural aversions to the bitterness of coffee or the harshness of tobacco, but those substances have some addictive qualities, which might make them desirable.
Capsaicin , the compound that provides the mouth-watering punch of chillies, does not seem to have any addictive qualities whatsoever.
And yet the preference for capsaicin is almost universal; nearly every culture has incorporated it into their cuisine in some way, for milllennia. These fiery foods made their debut in the Old World when they were brought back by Columbus and other early explorers. In spite of their initial unpalatability, they became accepted as a basic part of the diet in many parts of the world: west and east Africa, India, south-east Asia, parts of China, Indonesia, Korea, and other smaller geographic regions, such as Hungary.
Most young children, even from cultures known for their spicy recipes, are averse to capsaicin. So maybe, then, instead of actually liking the pain, we're merely desensitising ourselves: what used to be really painful is now just sort of painful.
Since capsaicin is a member of the vanilloid family of molecules, it binds to a receptor on the tongue called the vanilloid receptor subtype 1. Upon binding to the VR1 receptor, the sensation produced by the capsaicin molecule is the same sensation that heat would cause, which explains capsaicin's burn. TRP receptors are known to be sensitive to changes in temperature and are likely responsible for temperature sensation.
When chilli peppers are the source of the capsaicin, there isn't any actual tissue damage; but because it binds to the TRPV1 receptor, the brain is tricked into believing that the tongue truly is on fire. In , Rozin and a colleague, Deborah Schiller, reported a study in which they compared the pepper preferences of Mexicans and Americans.
Mexicans generally eat chillies several times per day, while Americans only eat chillies a few times a week. If desensitisation could explain our preference for oral pain, then Mexicans should show higher tolerance for capsaicin than Americans, and Americans should more easily detect capsaicin, even in small amounts, than Mexicans.
The data only weakly supported these predictions: the differences were seen, but were not statistically significant. Another prediction made by the desensitisation hypothesis is that individual tolerance should increase with exposure, and therefore with age. Rozin and Schiller found no correlation between age and tolerance though.
Experiments conducted to try to induce a preference for capsaicin in rats, using traditional reinforcement techniques, proved futile. In the late s, Frito-Lay tried to market a brand of corn chips in Mexico that had the flavour of chilli peppers, but without any capsaicin.
As would be expected in a culture that actually enjoys the burn, the product was a failure. Likewise, bell peppers, which have some pepper flavour but no capsaicin, are not at all popular in Mexico. While most scientists still do not quite have a handle on the human preference for spicy foods, the best explanation comes from a mechanism called "hedonic reversal", or "benign masochism".
Effects of Capsaicin David Julius and Michael Caterina want to find the molecule in our body that responds to peppers' heat. Grains of Inspiration As a water bottle is constricted, sand grains move slightly apart and water runs down to fill in the gaps. Description Once again, Alan Alda discovers that the trivial often yields the profound or at least the unexpected.
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Only available in USA and Canada. Other Titles You Might Like. Human: The World Within. Body Fantastic. On Land. Homo Spatius. Taste and Smell. Just the Facts Senses Series.
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