Picture this. You bite into a bean burrito, and your mouth is filled with many different and delicious tastes. You recognize one in particular - cilantro! Cilantro tastes great in burritos, on salads, and infused in oils. But your friend can't stand the taste of it! They think cilantro tastes like soap. Why do your brains process the taste of cilantro so differently?
To answer this question, we must dive into what part of the brain processes the sense of taste. What we understand about taste has changed over the years because it's quite a complicated process! Now that COVID-19 has changed what we know about smell and taste, scientists have even more questions about this sense.
What Part of the Brain Processes Taste?
The center of taste perception and processing is the primary gustatory cortex. It consists of two substructures on the insular lobe and within the frontal lobe. The gustatory cortex is the final stop for information gathered by the taste buds.
But the journey from the tongue to the brain is a little more complicated than that. Let's dive a bit deeper into how our brains process taste.
How Taste Receptors Work
Taste begins with the taste buds, small structures that contain gustatory cells. Did you know that you may have up to 10 million taste buds inside of your face at any given time?
Taste buds aren't only located on your tongue. You can also find taste buds on your:
- Soft palate
- Upper esophagus
- Epiglottis (a small flap of tissue that directs food to your esophagus and prevents food from going down your windpipe)
If you have learned about taste in elementary school, you may have seen a map that shows "where" taste is detected on the tongue. In the 1970s, that map was proven to be false.
In fact, each taste "bud" contains 50-100 receptor cells that gather information about the molecules in your food. (Did you think your tongue knew so much about organic chemistry?) The recognition of different molecules is what helps us recognize salty, sweet, bitter, sour, or umami flavors. Salty tastes, for example, contain a high concentration of sodium ions. Sour tastes contain a high concentration of hydrogen ions.
Different molecules trigger different action potentials in different ways, producing different "tastes." (Action potentials are the way that neurons communicate with each other!)
But before we can recognize a sour candy or bitter herb, the information our sensory receptors collect must take a journey to the brain.
From the Taste Buds to the Thalamus and Beyond
Information from taste receptors travels through three cranial nerves to reach the brain:
- Facial nerve
- Vagus nerve
- Glossopharyngeal nerve
The first place these taste receptors travel to is the brain stem. Then, they head to the thalamus and eventually end up in the gustatory cortex.
In recent years, scientists have identified specific places in the gustatory cortex that "light up" when we taste food. They also have identified where we process different tastes. As it turns out, it's not a map of our tongue that we should use to "map" different tastes, but a map of our brains!
As these different tastes are registered by the brain, signals are sent out to take action. At the same time that our brains are recognizing the salty taste of fries, it's telling the stomach to start breaking those fries down!
Are Taste and Smell Processed in The Same Part of the Brain?
Yes and no. Scientists say that taste is 80% smell. Why is that? It's important to know that smell only takes place when gaseous particles reach our olfactory receptors. As we chew, we break down the food we are eating and those particles are released into the nasal passage. We are processing smell and taste at the same time!
These two senses are also closely linked because they collect information through chemoreceptors. Our bodies collect information about vision with the help of photoreceptors. When it comes to touch, hearing, and balance, we recruit the help of mechanoreceptors. (And yes, "balance" is considered a sense, just like our five senses!)
Another thing that makes taste unique is that our taste receptors are processing what is happening inside our bodies. What we see, hear, smell, and touch is most likely outside our bodies. For being one of the five senses, taste is pretty unique!
Are Taste Preferences Genetic?
So we know that taste receptors pick up different molecules in food. With that knowledge, our brain forms our perception of taste. How does this explain why some people perceive cilantro as delicious and some as soapy? The answer is in our genetic makeup.
Among all the molecules that make up cilantro are organic compounds called aldehydes. Aldehydes tend to be soapy in nature (like formaldehyde). But if you are a person that loves the non-soapy taste of cilantro, your taste buds just can't detect the aldehydes in this herb. If you taste soap, your genes have a variation that allows you to take those aldehydes in a big way. Who knew that tasting cilantro as soap meant you have abilities that other people don't?
Why Can't People Smell or Taste When They Have COVID?
In 2020, you or a friend might have experienced another strange taste-related sensation. Maybe onions and garlic started tasting terrible. Or sodas tasted like metal. Some people started experiencing "hallucinations" in which they tasted things that didn't exist. This happened to people who contracted COVID-19. Why? We're not exactly sure.
It's not uncommon for people to lose their senses of smell and taste during an upper respiratory infection (URI). This is also known as "asomnia." During the infection, mucus gathers throughout the nose and blocks the olfactory receptors. Those receptors simply can't collect the information needed to send it to the brain, and the brain doesn't know there is anything to smell. Because smell is so closely correlated with taste, the taste is often reported to be dulled during a URI, too.
That much we know about a common URI. But what about COVID-19? Not only did people lose their sense of smell while infected with the virus, but many lost their senses for months on end. In some cases, people would lose their sense of taste, regain it, and then notice distortions months later.
Scientists are still not quite sure why this is. Fortunately, research so far leads them to believe that COVID-19 only affects the initial taste and smell receptors. The brain seems to be safe. It may take years before we can fully explain why people have lost their sense of smell and taste.
Will Taste Come Back After COVID?
Loss of taste or smell was an indicator for many people who had the COVID-19 virus, even if they didn't experience other symptoms. Your senses are likely to return after 4 to 6 weeks. Why? Because all cells regenerate around that time. Even if the receptors themselves are attacked by the virus, they are likely to regrow and begin functioning like normal.
If you have had COVID-19 and have lost your sense of smell or taste for more than six weeks, reach out to a medical professional.