Hey there. It's Dr. Susan Peirce Thompson, and I want to talk to you today about something called reward prediction error and how it relates to food addiction recovery. To your Bright Line Eating® journey. In particular, this is going to be the first of a series of three vlogs that are going to cover some of the science that I'm digging deep into as I write my new book, which is a memoir. It's half memoir, half science, and it's all about the dopamine dominant brain. It's called Addiction And...The Wild Ride and Upside of a Dopamine Dominant Brain, which I have, and maybe you have too. This first blog is all about dopamine and reward prediction error.
We talk about dopamine in Bright Line Eating terms as a molecule that relates to craving. Dopamine wants. It craves. It anticipates. It pulls us toward. And how this relates to our food journey is if we've been eating a lot of ultra-processed foods, a lot of sugar and flour foods, the dopamine receptors in the reward centers of the brain, they get depleted, they get downregulated, which means fewer receptors, they're less numerous, less responsive. What that means is we have to keep eating highly rewarding sugar flour foods in order to just feel okay throughout the day. This is problematic because those foods aren't healthy and that causes all kinds of downstream effects, Type 2 diabetes ,and all the things, not to mention powerful cravings to pull us toward eating those foods to make us feel okay.
I want to talk to you about some of the seminal research that shows a related but somewhat distinct function of dopamine, which is to track our expectations and what comes down the pike in relation to our expectations. In other words, is what's happening in life better than we expect? About what we expect? Worse than we expect? It's dopamine that's tracking that and it's tracking that in order to help us learn how to tailor our behavior to get what's better than we expect, to get what's good in life. Dopamine is the one that's keeping score. It's the one that's keeping track.
And it was Wolfram Schultz, who was a neuroscientist in Switzerland in the late 80s, early 90s who did a series of studies with macaque monkeys that showed how dopamine works in this regard. He had the macaque monkeys sit there and he would either play a tone or flash a light, let's just say a light. So, a light flashed and then a second later the monkey got a drop of juice. As this was all happening, Professor Schultz was monitoring dopamine receptors where in the addiction reward centers of the brain, the ventral tegmental area, the substantia nigra in particular. This is the core. The nucleus accumbens is right by there. This is the core of the addiction centers in the brain. And so, he's measuring dopamine rates and you can measure dopamine rates there and you can see firing rates are going to be not zero at baseline. They're going to be something. So, the dopamine neurons are firing a little bit, little bit. But when the juice arrives, the dopamine neurons fire a bunch. They get excited about the juice. This part of the brain was designed to steer us towards sugar and to steer us towards sex and other highly rewarding things. So not surprising, the juice arrives, the dopamine neurons go crazy. They're like, "Yay, juice."
What's interesting is as this little simple trial gets repeated, light flashes, a second later juice arrives, the dopamine neurons get hip to it, and they change their firing pattern. What happens is as they learn, they actually stop firing to the juice and instead they start firing to the light. Now this is like Pavlov's dog, right? The salivation comes at the sound of the bell before the food is even delivered, right? It's the same phenomenon. These dopamine neurons, they fire when the light comes. It's like they're saying, "Yay, juice is on the way." Here's the light. Juice is on the way. But then a second later, the juice arrives and the dopamine neurons have already gone down to firing at baseline and they don't change from that. It's almost as if they're saying, "Yay, juice is coming. Oh, here it is. Yep, just like we expected. Meh." So, if the reward that comes is just as expected, the dopamine neurons stay flat. They've already come back down from the initial big spike of firing to the light, which they're now excited about. The light. Oh good, juice is coming. Now, back down and now meh, okay, the juice arrived. No big deal. We were expecting it.
What's interesting is if the light flashes and a second later a whole bunch more juice than one drop arrives, now the dopamine neurons are excited about that. Yay, we got more juice than we expected. That's awesome. And what's really interesting is that if no juice arrives right on cue at the exact moment when the juice was supposed to arrive and it doesn't, those dopamine neurons go eerily quiet, suppressed like, "Oh, this is sad indeed. This is bad. We were supposed to get juice. No juice." And so, these neurons know what's supposed to come and when. They're watching and waiting and tracking and they're going to let you know.
How does this relate to your Bright Line Eating journey? Who cares? By the way, this is all called reward prediction error. Like error, what's the difference between the reward you expect that you were predicting and the reward you actually get? This is actually why a paycheck deposited into your account every two weeks doesn't actually give you a big thrill, even though that amount of money, if it were a surprise, would be a huge thrill. But you're expecting it. It's no big deal to your brain. Rewards that are expected are not a big deal. This is why end of year bonuses are not a great idea because if people just expect them, they don't feel like a bonus. A good bonus comes out of nowhere and is paired with a really clear explanation of what someone did above and beyond to earn this special extra thing. Oh, the brain's going to take notice of that. But an end of year bonus that's about what you always get at the end of the year, that's not even a bonus. That's just a bigger paycheck and nobody's brain is super excited about that. Maybe the first year they are. After that, not so much.
So, how does this all relate to your Bright Line Eating journey? Well, first of all, it's helping the brain train you up to follow Bright Lines in the first place. Here's how this works. As you probably know, the Bright Line Eating food plan is far more structured than most people eat, not just in terms of what to eat, but when, right? I teach people to eat breakfast at breakfast time, lunch at lunchtime, and dinner at dinner time. Now, it's not a requirement. It's just a suggestion and that's how most people start out. What's interesting about that is it has a big impact on the dopamine neurons in your brain because as you set up your Bright Line Eating journey and let's say you enroll in Boot Camp and you embark on your Bright Line Eating journey, sticking with it suddenly becomes the reward. It's exciting to stick with it. It's sort of like, "Oh my gosh, this is working. This was supposed to be what I was going to eat and now it is what I'm eating and that's amazing and I didn't know I could do it." Most people, when they start Bright Line Eating, their expectations of being able to do it are actually quite low. For a lot of people, very low. They really don't expect themselves to be able to do it. What that means is that reward prediction error gives them a big spike in dopamine when they have a Bright meal. It's kind of like, "Whoa, here I am. I wrote this down last night and it's actually what I'm eating, hot diggity. This is amazing." That spike is powerful.
Now, after you've been Bright for a week or two, now your brain is trained up and you're no longer that excited when you have lunch at lunchtime. Your brain now expects you to have lunch at lunchtime, but check this out. Now, your brain gets excited when you're about to have your Bright meal because the time of day is so predictable that that in and of itself is the signal. The time of day, mealtime becomes the light and your brain starts to fire to that. Dopamine starts to go off of "it's mealtime. We're about to have our Bright meal." That's good. The reward is coming and you get this dopamine surge at mealtime because you're about to have your Bright meal and that pulls you toward the Bright meal because the way the brain works is dopamine pulls you toward what it wants, and it sucks you in. Now you're actually pulled toward the Bright meal. It makes it so easy to go have that Bright meal. It's what your brain wants. It's what your brain is propelling you toward. Now you sit down to have the Bright meal, it's no big deal. Now it's like, "Meh, all right." And that's what we expected. We thought we were about to have a Bright meal. We're having a Bright meal. No big deal.
This is what we start to call food neutrality, where, okay, you're just living your Bright life. You're having a Bright meal. Now, this predicts some interesting phenomena. If you sit down and you have the Bright meal, and for some reason it's disappointing, sometimes a meal just feels gimpy. It just feels like, "Oh, that wasn't very much, or I thought it would last longer, or I thought it would be more." I don't know if you've ever had this. I certainly have had this phenomenon where I sit down, I'm eating my Bright meal and halfway through it, I'm already grieving the end of the Bright meal. I'm like, oh my gosh, I can't believe this is almost over. I'm going to have to wait so long till my next meal. It feels like a death. And if you had some sort of expectation that the meal was going to deliver a certain satisfaction and now you've had the meal or you're having the meal and it's not, that's a negative reward prediction error. That's going to cause a dip in dopamine that's going to feel pretty devastating. It's going to feel bleak. That's why sometimes you sit there finishing up your Bright meal and you feel like somebody died because it feels awful to have expected so much out of a meal and to have it under deliver.
Here's another interesting phenomenon that it explains. Have you ever had to eat your Bright meal really late for like a wedding where God bless, they have the ceremony at six, and they cater a meal at 8:30 or nine o'clock at night and then you don't actually get it till nine o'clock at night. I mean, sometimes in that circumstance, I would eat my Bright meal before I go, but let's imagine you don't. I've had the situation where I don't and I wait and I'm going to eat at the wedding. I've called in advance. They're going to have food I can eat. I want to eat with everybody. And it's now seven o'clock, eight o'clock, 8:30, quarter to nine, almost nine o'clock. They haven't even brought out the salads yet and I'm going out of my mind. It's interesting because I'll sit there and notice I'm not actually that hungry. Maybe I was hungry two or three hours ago, but do you ever notice the hunger pangs actually pass? You just drink a glass of water and they pass. So, it's not even that I'm hungry, I'm fine, but I have this intense yearning for the frickin' food already. I want that food and the wanting is so intense. It feels like a rubber band that's being stretched beyond what it can barely tolerate and I'm about to snap. Then the food is served and I survive. But what's interesting is reward prediction error would explain that because my brain expects dinner around five or six o'clock at night. And then when it doesn't come, there's a dip in dopamine that lasts and lasts and lasts and the wanting is there and it's like, where's my meal? Where's my meal? Where's my meal? And my poor brain, again, it's not hunger. It's wanting, it's craving. And I'm not craving junk food. I'm craving my fricking Bright meal already, right? Isn't that interesting? Anyway, that's a phenomenon that reward prediction error explains. I'll actually be circling back to this topic later on in a couple of these other vlogs that I'm shooting for you for the next couple weeks.
I just wanted to tell you a little bit more about the science of dopamine because dopamine is a fascinating molecule. Today we covered reward prediction error, and it just shows how this is all about learning. That's what the scientific community would say that this is about dopamine's role in learning, but it's also dopamine's role in addiction. And so, what that shows is that addiction is really a turbocharged case of learning. It's like learning run amok. It's the learning architecture of the brain hijacked and a galloping horse running away. That's what addiction is.
I also want to point out that it's super interesting that since the 1950s, and we're going to talk about some experiments next week and the week after that are way older, since the beginning, including the experiment I told you about today, juice, when neuroscientists want to study addiction in the addiction centers in the brain, they use sugar. They use fructose or glucose or some sort of food or some sort of hyper palatable food. That's what they use. They never think twice about it. There was never even a settled question of is food addiction real? Decades and decades ago, neuroscientists have always known that sugar affects those areas of the brain, food, glucose, fructose, sugar, all of them, same, same, same, affect the addiction centers in the brain and they're easier to use than drugs or whatever. They're just easier to use. And so, almost all of the seminal addiction studies in animals have been run with sugar or food. I just find that really interesting because you'll find eating disorders experts still saying that food addiction's not a thing. God bless them. Neuroscientists have been quietly using juice for their addiction experiments and their dopamine experiments all along.
That's the weekly vlog. Can't wait to share some more science with you next week and the week after. This is Dr. Susan Peirce Thompson. I'll see you next week.
