06/23/2016

Your sense of taste, also known as your gustatory perception, is likely a sense you’ve devoted a lot of thought to without considering how it really works. After all, eating food we enjoy is more than a survival practice—it’s a daily activity that food bloggers and home cooks have turned into hobbies (or full-time careers). Unlike our sense of hearing, sight, or touch, our sense of taste responds to chemicalstimulation, rather than physical ones.

The tongue, our taste organ, has between 2,000 and 5,000 specialized chemical receptors on its surface. We call them tastebuds, and they are responsible for translating chemical signals into “flavors” we can perceive. Tastebuds come in 5 different varieties that make it possible for us to experience the wide spectrum of flavors we enjoy (or don’t) on a daily basis.

The 5 fundamental tastes our tastebuds perceive are:

  • Sweetness
  • Bitterness
  • Saltiness
  • Sourness
  • Umami

Most people are familiar with the first 4 tastes, but umami was only discovered and studied in the last century. The word itself is Japanese for “yummy,” as it was discovered by Japanese chemist and early 20th-century foodie Kikunae Ikeda. Unlike the other tastes, umami does not perceive a specific type of flavor—it simply perceives “deliciousness,” or what is pleasurable to eat. Some have described it as the “savory” sensation. Monosodium glutamate, commonly known as MSG, was artificially designed to stimulate our umami receptors—which is why it was a popular component in commercial food processing for a long time.

APPETITIVE VS. AVERSIVE FOOD

Now that we’ve covered the basics, we can cover some of the interesting neurological properties of gustatory perception. Foods we eat fall into two categories: appetitive and aversive. These are scientific terms for “food you like” vs. “food you hate.” Far from being superficial preferences, your brain actually processes aversive food in a different part of the temporal lobe than appetitive food. If you remember from our temporal lobe blog, this is also the part of the brain where emotion is processed.

Some research indicates that appetitive food triggers the release of serotonin and dopamine, neurotransmitters that contribute to a sense of focus, mood stability, and well-being. While aversive food may also trigger dopamine, it also activates the sympathetic nervous system—also known as the fight or flight response. The release of epinephrine or norepinephrine is why spicy or bitter food makes us sweat or causes our pupils to dilate.

The fight or flight response makes sense in a survival context—aversive food serves an important purpose, as it is how our body warns us against eating poisonous substances.

HOW THE BRAIN PERCEIVES TASTE

There are 4 cranial nerves that receive signals from the tongue: cranial nerves 5, 7, 9, and 10. These nerves travel straight from the tongue to the brainstem. Cranial nerves 7, 9, and 10 send traditional taste signals to the brainstem, but cranial nerve #5—the trigeminal nerve—transmits information about the texture and spiciness of food.

The tongue projects its information to the thalamus in the forebrain, which is a kind of “relay center.” It ensures that signals received by the brainstem travel to the correct parts of the brain. Once the temporal lobe receives the taste information and processes it, it can be integrated with other senses in order to assign meaning to it.

(It’s worth mentioning that all of this happens in a matter of milliseconds. While your sense of taste seems simultaneous with the moment food touches your tongue, you are not actually “tasting” your food until the information reaches your temporal lobe.)

Gustatory perception is tightly linked to other senses and brain functions. Once processed, taste signals are compared against our sense of smell, temperature, and texture. It is also compared against our emotional system and memory to determine if we enjoy what we’re eating. Your sense of taste is also linked with your hypothalamus—the part of the brain that controls the sensation of hunger, digestion, and hormones.

Interestingly, your sense of taste is also tied to the function of the Edinger-Westphal nucleus. If you remember ourblog on the sense of sight, this cluster of neurons is responsible for controlling pupil contraction. Your taste and appetite is literally linked to your eyes—bringing a layer of truth to the phrase “My eyes were hungrier than my stomach.”

TASTE DISORDERS

There are both neurological and metabolic disorders that affect the sense of taste. Addison’s disease, pituitary gland problems, and cystic fibrosis have been known to affect the sense of taste. Interestingly, the effect is often to make taste more sensitive, rather than less. While there are no adverse affects to having a heightened perception of taste, it can be uncomfortable for some people.

The taste disorders are categorized according to their effect on perception:

  • Ageusia — No sense of taste
  • Hypogeusia — Reduced sense of taste and smell
  • Dysgeusia — Distorted taste, or changed taste
  • Parageusia — Perceiving an always-present abnormal taste
  • Hypergeusia — Heightened sense of taste; creates “supertasters”

Hypogeusia is a normal condition for many people past age 50, but it can also be the result of degenerative brain disease. Our ReceptorBased® rehabilitation specialists can help our patients determine if their lack of gustatory perception is the result of degeneration. Parageusia is the condition that causes people to sense a “metallic” taste in their food (or any other abnormal taste).

What makes hypergeusia unique is that while it is an abnormal condition, it isn’t necessarily a “disorder” in that it reduces function or disrupts daily life. In fact, some people have turned hypergeusia into vocations as food writers, chefs, or wine-tasters. Being able to perceive unique and subtle flavor notes can be an asset to many. Unfortunately, for those who simply want to eat food without being picky, hypergeusia offers a level of discernment some diners might find unbearable.

TRANSLATIONAL NEUROLOGY

At Plasticity Brain Centers, we practice what we call “translational neurology.” That’s our term for taking academic knowledge and applying it in a clinical context. Everything we discuss about the senses is widely-known information. What makes our neurological specialists unique is how we turn that information into therapies that improve and restore brain function for our patients.

For example, taste is processed in the temporal lobe. That would make it possible to improve temporal lobe function by stimulating your tastebuds. While we normally don’t use food during our rehabilitation sessions, we can provide dietary recommendations to our patients with disorders that affect the temporal lobe. This includes patients with PTSD, Alzheimer’s, epilepsy, Parkinson’s, and any degenerative brain disease. One exercise involves patients eating food and recalling the events and emotions associated with that food, which exercises temporal processing.

Another potential use of taste receptors is helping improve dry mouth or constipation. The part of the nervous system responsible for digestion is known as the parasympathetic system, or the “rest and digest” response. This response is triggered by both taste and smell—highly fragrant cooking, such as cooking garlic and onions, can activate this response prior to actually eating. Patients can use fragrant food to help generate saliva and promote gastric motility.

CONTACT OUR RECEPTORBASED® REHABILITATION SPECIALISTS

Plasticity Brain Centers is committed to helping people live better lives through improved brain performance. Using cutting-edge diagnostic tools and research-based procedures, we can target any low-performing regions in your brain and use ReceptorBased® therapies to improve or restore function. Whether you’re a high-performance athlete or in the early stages of degenerative neurological disease, our renowned neurologists have the tools and experience to help you. Call our office today to learn more.