How the Brain Reacts to Taste

Charles Zuker, Ph.D., is fascinated by how sensation turns into perception in the brain. The Chilean-born researcher received his doctorate at MIT, spent more than 20 years conducting research at UC San Diego, and now works as a Professor of Neuroscience and Biochemistry at Columbia University. Last week Zuker gave a presentation, “Common Sense About Taste,” at the Carlyle Hotel organized by Columbia University as part of a lecture series sponsored by the Dana Foundation.

If you take a (small) sip of milk and stick your tongue out in front of a mirror, the pink dots that appear in contrast to the milk on your tongue are mushroom shaped, fungiform papillae—a type of taste bud. One taste bud contains 50 to 100 taste cells. Each cell’s membrane is freckled with receptors that “taste” the surrounding chemical environment. Thus a single
taste bud is equipped to sense sweet, salty, sour, bitter, and umami—the savory taste that owes its name to the Japanese word for “yummy.”

Zuker began his lecture by highlighting the evolutionary importance of our distinctive tastes: The sweet, salty, sour, and umami tastes maintain metabolic, osmotic, pH, and protein homeostasis in the body by triggering attractive or aversive feeding behaviors. Bitter taste triggers aversive behaviors; a single bitter taste cell has scores of receptors that detect hundreds of different bitter compounds—many of which are known toxins.

Through a battery of transgenic, behavioral, and neurosurgical methods, Zuker and his colleagues have deciphered many mechanisms that connect taste sensation to brain perception. Beginning with the tongue, in 2000, Zuker’s team identified the first taste sensors, T2R bitter receptors, using new data from the human genome project. They went on to identify receptors and cells for the four other tastes.

Zuker’s presentation, like his research, began at the tongue and moved to the brain, from perception to sensation. He explained that the signals from taste cells move through nerves and several neural stations to the taste cortex, the insula. Zuker and his lab discovered that the insula contains taste-specific constellations of neurons that make a gustotopic map with distinctive sweet, salty, bitter, and umami sections. His research revealed that tastes—like our somatosensory, auditory, and visual systems— are mapped spatially in the brain.

After elucidating the path of taste from sensation to perception, Zuker now focuses his taste research on how the gustotopic map in the insula creates behavioral reactions and salient memories.

In a Q&A following the talk, Zuker said he believes that his research could eventually improve people’s quality of life via novel treatments for eating disorders and obesity:

We can use the logic of [taste] receptors to come up with ways to enhance the
human sensory experience, and make our lives healthier and easier… to engineer
a system where a little bit of sugar [or salt] tastes like a lot. Can we fool
your receptors? The answer is yes… for those of you who enjoy biochemistry,
this is through the use of allosteric modulators—little molecules that when
they lock onto receptors they have no taste, but they make the receptor fire a
lot more, with just a tiny bit of activity.

Perhaps individuals will someday be given the choice to make 100 calories taste like 1,000 calories. As we learn more about the pathway between tongue sensation and brain perception of taste, sensory modifications such as these will likely enhance our health and well being.

–Charles Sadle

One response

  1. O brave new world, where chemicals continue to fool our senses — where we might make 100 calories taste like 1,000. Or, maybe, we could just lower our expectation and excitement levels. It’s called smaller portions.

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