Know Your Brain: The Gustatory Cortex — How Taste Works



We eat to live, not live to eat — but the experience of being alive is more closely intertwined with eating than you probably thought. There’s a reason you’ve been looking forward to that weekend cookout, or the first barbecue at the beginning of spring — something you’ve planned since the first warm day of the year. We don’t just taste our food — we savor it and then crave it, a craving that is often dependent on our mood. Far from just keeping the blood sugar up and providing your body with nutrients, the relationship between food and the brain is a complex one — made even more intriguing in recent years with a flourish of new discoveries.

Taste receptors on the tongue, the roof of your mouth, and even the upper esophagus, come into contact with the molecules of food in your mouth. These microscopic buds then relay information to the brainstem, to a region known as the primary gustatory cortex. This portion of the brainstem actually contains two smaller substructures: the anterior insula, located on the insular lobe, as well as the frontal operculum, found on the brain’s frontal lobe. Extracellular unit recording technology has allowed us to observe the differences in how neurons within the gustatory cortex react when you eat a ripe, savory tomato slice, or bite into a sour lemon. Each evokes a different experience, and so the gustatory cortex is far more than just a database of different tastes.

Taste cells form connections with the tails of neurons that run throughout the superficial petrosal branches of the facial nerve, the lingual branch of the glossopharyngeal nerve (used by our tongue for speech), and the superior laryngeal branch of the vagus nerve, all of which supply stimulus to the taste buds. What we see and smell (just imagine yourself walking down the aisle, eyes moving over each tray at a breakfast buffet, before you end up piling bacon and fresh fruit onto your plate), is thrown into this mix along the way — picked up by neurons in the orbitofrontal cortex, which then relay the message along to the gustatory cortex. Sure, it’s easy for your eyes to be bigger than your mouth, because there’s a whole lot happening here when you’re picking out your food.

We like to think of flavors coming from our mouths, but actually the smells you breathe in mix with smells picked up from the back of your throat (which the brain perceives as signals from the mouth) to help the anterior insula identify the food you’re eating. This is why you might describe tasting the smell of vanilla — but if you mixed the same scent with a salty taste, the flavor becomes unrecognizable, making the whole greater than the sum of its parts. The gustatory cortex even considers our food’s texture.

The smells of bacon and freshly brewed coffee that fill your nostrils, as they waft across the room, travel to two different parts of the brain — the hippocampus, which deals with memories, and the temporal lobe, which deals with speech. As with smell, food is capable of invoking distant memories — like the pancakes you had for Sunday breakfast growing up. Sometimes, the flavors themselves are even more vivid than the memories. Because speech is so secondary to the whole experience, there are tastes that we don’t always have words for, which may be why the discovery of receptors for “umami” only happened quite recently.

As we eat, our brains have to know what we’re eating — when to chew and swallow, but also whether or not we like what we’re eating. The close connection between memory and food functions a bit like reward circuitry — it’s how we remember what selection to make at the buffet and what to avoid, particularly if the buffet in question is one we frequent.

About 34.2 percent of the neurons in the gustatory cortex are what you would call chemosensory neurons — those that differentiate between the tastes as well as recognize those tastes which are absent or present, letting you determine whether your eggs need salt, or if your toast has been burned. The gustatory cortex also connects the prefrontal cortex of the brain (which is heavily involved in regulating our emotions) to the brain’s insular cortex.

While our receptors for flavor function as reward, it can just as easily work against us. Having a bad experience with fish in the past — whether you disliked it, or choked on a bone — could make you averse to similar foods. It may actually play a bigger role in your well-being than you may think. People who suffer from eating disorders, such as anorexia — marked by self-starvation and a refusal to eat — are more likely to have reduced responses to pleasant, sweet and savory flavors.

In one study conducted by researchers from the University of Pittsburgh and the University of California at San Diego, functional MRI technology was used to monitor brain activity in 32 women. Half of them had recently recovered from anorexia nervosa, but those who served as the study’s control group showed a stronger relationship between how they enjoyed more pleasant flavors and activity in the insula, which was not seen in those who had a history of eating disorders.

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