It’s Christmas time! Your eyes are full with winking colourful lights, soft white snow covers the streets and your taste buds awaken when you think about that sweet, fragrant gingerbread you are used to having every year! But wait… How can you remember it so well? Scents and flavours are powerful time machines and can, more than images and sounds, throw us back to the past. Neuroscientists have always been fascinated by this phenomenon and tried to understand more about it.
When biting into a gingerbread cookie, its smell travels to the so called glomeruli in our nasal cavity and its sweet taste reaches thousands of taste buds on our tongue. Both these structures contain hundreds of thousands of tiny nerve endings that, once activated by scents and flavours, send messages straight up to the brain. These signals run much faster than your car! At a speed of about 50m/s (180km/h), they travel through two relay stations in the central nervous system, the medulla and thalamus, before reaching their final destination, the gustatory cortex. Here, millions of neurons are ready to receive and process the messages sent by the tongue and assign them an identity. This is when you realise that your cookie is sweet, not too gingery, and has a nice hint of cinnamon! Neuroscientists at the Columbia University in New York, have now demonstrated that the perception of different tastes is mediated by different areas in the gustatory cortex. Using a technique called optogenetics, they were able to artificially activate or shut down what they thought were the bitter and sweet areas in the gustatory cortex of laboratory mice. Then, they trained mice to lick from a water bottle while their cortex was artificially activated. Mice whose bitter area was activated when licking progressively reduced their licking. On the other hand, mice whose sweet cortical area was activated during the task showed a marked increase of the licking behaviour [1].
But this has got nothing to do with remembering the familiar and delicious taste of our grandmother’s gingerbread cookies, right? Correct! The message in the gustatory cortex keeps travelling though our nervous system, and reaches the so called limbic system. This is the most ancient part of our brain and contains areas that are strongly implicated in processing emotions and memories. In particular, the hippocampus (from the Latin sea horse, for its shape) receives signals from the gustatory cortex and matches them to signals that have already travelled through our brain, and for which a memory has been established. This is how your brain safely keeps the secret of your grandma’s cookies. Be reassured, you will never forget it!
[1] Peng, Y. et al. Sweet and bitter taste in the brain of awake behaving animals. Nature 527, 512–515 (2015)
About the authors
Mariangela Panniello (Text) is a neuroscientist based in Oxford, where she studies the neuronal basis of perception. She’s interested in telling everyone how cool the brain is, in finding out new ways to make scientists from different disciplines work together, and in making science more friendly for the general public.
Andrea Ferrari Trecate (Illustration) is an environmental journalist based in La Spezia (Italy) and a brilliant amateur illustrator.
Supertaster Experiment
Did you know that most of us have between 2000 and 10000 taste buds, but 1 in 4 people have an unusually high number of them? This makes them supertasters! Try yourself whether you’re among them!
What you need:
- Bottle of blue food dye
- Cotton buds
- Tweezers
- Hole punch reinforcers
- Magnifying glass
- Taster chart (see below)
- Damp cloth or tissues
Instructions
- First check that you’re not sensitive to the food dye’s ingredients!! Place a cotton bud into a bottle of blue food dye. Once it is well coated, stick you tongue out and, guided by a mirror, dye the front third of your tongue.
- Carefully place a hole punch reinforcer on to your tongue. If you don’t have any reinforcers you can use a hole-punch to create a hole in a small square of waxed paper.
- Ask a friend to count how many pink bumps they can see on your tongue inside the ring reinforcer - try to keep your tongue still! They may find it easier using a magnifying glass.
- Now check out whether you have super tasting powers!
- fewer than 15 papillae (non-taster)
- 15 to 35 papillae (average taster)
- more than 35 (super taster)