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

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.

My pleasure.

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, et cetera?

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 we can, is what we can operationally define as perception. In the senses, let's say olfactory, odor, taste, vision, you know, 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 just 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, the maniacal drive, eh, 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 felt 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 ba- the five basic taste qualities, sweet, sour, bitter, salty, and umami. Umami is a Japanese word that means yummy, delicious, and that's the, uh, 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. 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 licking, then you put a unhappy face, then you squint your eyes, and then you start gagging. Eh? And that entire thing happens by the activation of a bitter molecule in a bitter sensing cell in your tongue.