So let's think about dopamine peaks and baselines. And let's remember that for every peak, there's a trough. What do I mean by that? Well, when you have a wave, you also have the bottom of the wave. When you have a mountain, you have the bottom of the mountain. When we think about dopamine peaks and dopamine baselines, we have to include that trough because that trough, that is the level of dopamine below baseline, really dictates whether or not you are going to feel motivated to pursue something or not.

So I'm going to give you a visual in your mind. The visual in your mind is an increase in dopamine that's triggered by your desire for something. And really it could be your desire for anything. If you're hungry and you're thinking about, I really want a sandwich. I really want a, let's think, what sandwich would I want right now?

A really nice roast beef sandwich on sourdough with a slice of Swiss, tomatoes, slice of pickle. Here I'm describing the sandwich that I would want. So if you're hungry and you're thinking about that, dopamine starts rising. This is crucially important to understand. Dopamine is not just released when we get the reward, when we get the thing that we're pursuing.

Dopamine is released in anticipation of what we want. That increase in dopamine is by no happenstance, no mistake, relates also to our propensity and desire to move. Remember earlier I told you there's a separate circuit of dopamine that triggers movement and that when it's depleted is causing things like deficits in movement related to Parkinson's or other movement disorders.

Well, that's not pure coincidence. That's because desire and the need to move in order to pursue and reach goals are one in the same process. So if I desire a sandwich or I desire a cup of coffee or I desire some water when I'm thirsty, there's an increase in dopamine that we could call a little mini peak in dopamine.

But then here's the key thing. Very soon after I realized my desire for something, that peak that was caused by the desire comes down and drops below baseline, below the level of dopamine that it was prior to even thinking about the sandwich or the coffee or the glass of water.

And it's that drop below baseline that triggers my desire to go out and find that sandwich, that coffee, that water, or that blank, insert whatever it is that you happen to desire, action or substance of any kind or person, et cetera. So that drop below baseline is fundamental to the whole process.

And that drop below baseline was triggered by the preceding peak. So let's say that I desire a sandwich, there's an increase in dopamine. Then very quickly, it comes down below baseline just a little bit. Now I'm in pursuit of the sandwich. I'm looking for where I can get that sandwich.

I can order it, perhaps to be delivered. I can go out and find it. Now is the stage in which I have to think about what are the different stimuli, that is the things in my environment that signal whether or not I'm likely to get that sandwich or not.

And so for instance, if I were to go into my phone and order food on an app or walk down the street and see the sign for a deli, that's a cue that I'm likely to relieve that drop in dopamine and get not just back to baseline, but that I'll get a peak in dopamine.

And indeed that's what happens. If I find that deli, I go into the deli, they're open, they're making the sandwich that I want, they make my sandwich and great, I get that sandwich. And that sandwich will have some degree of inherent reward to it. Some degree of my liking it or not liking it.

So let's say I like it. It's not the best sandwich I've ever had, but all I'm doing is comparing my desire for that sandwich to the sandwich that I actually got and ate. And chances are, it's going to relieve that craving, meaning it will take that dopamine that had fallen below baseline, up, up, back to baseline.

And if I like the sandwich, it's going to indeed increase that dopamine, again, to another peak. Now, if I love the sandwich, like it's the most delicious thing that I've ever tasted in my entire life, well then I'll get a big peak in dopamine when I consume that reward.

However, chances are the sandwich is more or less as I expect it to be, which is pretty good. I'll eat it and I'm fine. What do I mean by fine? Well, there's a concept called reward prediction error. Reward prediction error says that the dopamine that it has experienced, that is, that's released from the VTA and nucleus accumbens, is going to be of a certain value.

And that value is going to be compared to the desire and expectation of what I thought I was going to get. So if you take what you actually got minus what you expected, that's reward prediction error. So if the sandwich is basically what I expected to get, fine, dopamine comes down basically to a baseline level that's pretty standard for me and is basically the baseline level I had before I ever thought about the sandwich at all.

If the sandwich completely surprises me and is completely amazing, just an amazing sandwich, well then, the level of dopamine that I experience when I consume that sandwich is going to be even greater and it's going to be that minus what I expected. So there, it's a bigger reward prediction error in the direction of higher peak by consuming the sandwich.

And then of course, there's the other possibility, which is the deli's closed or the sandwich they make me is lousy or it doesn't taste good or something happened in the consuming of that sandwich that just makes it a bad experience. In which case, if we take that reward experienced minus reward predicted from the initial craving, well then it's going to be less than what I expected and therefore the baseline drops below where it was prior to even desiring the sandwich.

Okay, so all of this might seem a little bit complicated, but it's all very simple. Desire for things increases dopamine, but then our level of dopamine drops below baseline and it's that drop below baseline that triggers the motivation to bring that dopamine level back up by going and pursuing the thing that you wanted in the first place.

Now, of course, as this is happening, you're not conscious of your dopamine levels. You experience this as context-dependent craving and pursuit. Because remember, the prefrontal cortex is involved in context setting and craving and pursuit because it relates to action and movement, which is one of the general features of the dopamine system.

So you can start to see how this is a beautifully designed system. And you can also see how it's a perfect system for desire and pursuit of anything, not just sandwiches, as I'm giving you in this somewhat trivial, but everyday and therefore applicable example. (upbeat music)