Essentials: The Biology of Taste Perception & Sugar Craving | Dr. Charles Zuker

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance. I'm Andrew Huberman and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my discussion with Dr. Charles Zuker. Charles, thank you so much for joining me today.

**Charles Zuker** (0:23)
My pleasure.

**Andrew Huberman** (0:24)
I want to ask you about many things related to taste and gustatory perception. But maybe to start off, and because you've worked on a number of different topics in neuroscience, not just taste, how should the world and people think about perception, how it's different from sensation, and what leads to our experience of life in terms of vision, hearing, taste, etc.?

**Charles Zuker** (0:48)
The world is made of real things. You know, this here is a glass. And this is a cord, and this is a microphone. But the brain is only made of neurons that only understand electrical signals. So how do you transform that reality into nothing that electrical signals that now need to represent the world?
And that process is what we can operationally define as perception.
In the senses, let's say olfactory, odor, taste, vision, we can very straightforwardly separate detection from perception. Detection is what happens when you take a sugar molecule, you put it in your tongue, and then a set of specific cells now sense that sugar molecule. That's detection. You haven't perceived anything yet. That is, yes, your cells in your tongue interacting with this chemical. But now that cell gets activated and sends a signal to the brain, and now detection gets transformed into perception.
And it's trying to understand how that happens that's been the maniacal drive of my entire career in neuroscience. How does the brain ultimately transform detection into perception so that it can guide actions and behaviors? So if I want to begin to explore all of these things that the brain does, I have to choose a sensory system that affords some degree of simplicity in the way that the input-output relationships are put together. And in a way that still can be used to ask every one of these problems that the brain has to ultimately compute, encode, and decode. And what was remarkable about the taste system at the time that I began working on this is that nothing was known about the molecular basis of taste. You know, we knew that we could taste what has been usually defined as the five basic taste qualities. Sweet, sour, bitter, salty, and umami. Umami is a Japanese word that means yummy, delicious, and that's nearly every animal species the taste of amino acids. And in humans, it's mostly associated with the taste of MSG, monosodium glutamate, one amino acid in particular. And so the beautiful thing of the system is that the lines of input are limited to five. And each of them has a predetermined meaning. You're born with that specific valence, value, for each taste. So sweet, umami, and low salt are attractive taste qualities. They evoke appetitive responses. I want to consume them. And bitter and sour are innately predetermined to be aversive. In the case of bitter, it's very easy to actually look at, see them happening in animals, because the first thing you do is you stop leaking. Then you put an unhappy face. Then you squint your eyes. And then you start gagging. And that entire thing happens by the activation of a bitter molecule in a bitter sense in cell in your tongue. It's incredible. It's again the magic of the brain, you know, how it's able to encode and decode these extraordinary actions and behaviors in response of nothing but a simple, very, you know, a unique sensory stimuli. This palate of five basic tastes accommodates all the dietary needs of the organism. Sweet to ensure that we get the right amount of energy. Umami to ensure that we get proteins and other essential nutrients. Salt, the three appetitive ones, to ensure that we maintain our electrolyte balance. Bitter, to prevent the ingestion of toxic, nauseous chemicals. Nearly all bitter tasting, you know, things out in the wild are bad for you. And sour, most likely to prevent the ingestion of spoiled acid, fermented foods. And that's it. That is the palate that we deal with. Now, of course, there's a difference between basic taste and flavor. Flavor is the whole experience. Flavor is the combination of multiple tastes coming together. Together with smell, with texture, with temperature, with the look of it, that gives you what you and I would call the full sensory experience. But we scientists need to reduce the problem into its basic elements, so we can begin to break it apart before we put it back together. So, when we think about the sense of taste and we try to figure out how these lines of information go from your tongue to your brain and how they signal and how they get integrated and how they trigger all these different behaviors, we look at them as individual qualities. So we give the animal sweet or we give them a bitter or we give them sour. We avoid mixes. Think of it as lines of information, yes, separate lines, like the keys of a piano, yeah, sweet, sour, bitter, salty, umami. You play the key and you activate a one chord. And that one chord in the case of a piano leads to a note, you know, a tune. And in the case of taste leads to an action and a behavior.