Kat Arney, The Naked Scientists
What’s your favourite flavour? Sweet? Salty? Or maybe the mysterious umami? This week Kat Arney has been tackling a tasty mythconception about the tongue.
Kat - If you cast your mind back to school biology lessons, you may remember seeing so-called ‘taste maps’ of the tongue, showing how we sense sweet tastes with the front of the tongue, salty with the sides of the tongue just behind, sour with side patches behind those, and bitter with an area right at the back. Then there’s umami, the so-called ‘fifth taste’ found in savoury flavours such as parmesan and anchovies, which is thought to be located in the centre.
This seems kind of logical, but if you’ve ever touched a salt and vinegar crisp with the tip of your tongue and felt that salty-sharp tang, you’ll know this can’t be true. So where did this myth come from, and what’s the real story?
It all started more than a century ago with a paper published by German scientist David Haenig in 1901. He’d been investigating whether different regions of the tongue were more or less sensitive to different tastes, by dripping different flavours across the tongue and seeing how much of each was needed to provoke a response. Perhaps unsurprisingly, given that taste buds are concentrated at the tip and sides of the tongue, he found that the tip and sides were more sensitive to all flavours, all the way round, showing his findings in the form of a rather confusing graph.
Four decades later, US psychologist Edwin Boring took a bit of artistic licence with Haenig’s data for a textbook that he was writing about sensory perception, portraying it as a map of the tongue with regions of different taste sensitivities – sweet at the tip, salty and sour at the sides and bitter at the back. This map quickly became accepted as scientific fact, and still persists in classrooms and books around the world today.
The truth is so easy to reveal that it actually makes a nice school science experiment – simply blindfold a willing participant, then gently swab different areas of their tongue with cotton buds soaked in different solutions – sugar water, salt water, vinegar and tonic water (which contains bitter quinine) – being careful not to make them gag, of course. Scientists now know that tastebuds all over the tongue can detect all five of the main flavours, not to mention some other sensations too such as the fiery burn of a chili pepper.
But according a paper published in the journal Science in 2011, there is one part of the body where different tastes are recognised by different areas, and that’s the brain. By dripping different liquids on the tongues of anaesthetised mice, the researchers discovered that distinct bits of the brain ‘light up’ with fluorescent dyes that reveal nerve cell activity in response to sweet, salty, bitter and umami tastes – but, intriguingly, not when they tested sour liquids. Their findings are controversial, as they conflict with results from other types of tests, but they do suggest that the taste maps we should be drawing are in the brain rather than on the tongue.