Pure Pedantry

Which is where step two comes in: On top of creating memories, dopamine controls the areas of the brain responsible for desire, decision making, and motivation. So once fries become salient, the next time you see or smell them, your brain releases a surge of dopamine that drives you to get more fries. When you succeed, your brain produces more dopamine, which reinforces the memory that made fries salient in the first place, etching it further into your brain. It's a never-ending cycle: The more you do something that's rewarding, the more dopamine makes sure you do it again. This is precisely how habits form. Eventually, if the fries become salient enough, your brain will release dopamine and push you to get fries anytime you see the colors yellow and red, even if you're nowhere near McDonald's.

And this is true for any behavior that results in a reward: Orgasms cause dopamine surges. So does hitting the jackpot when you gamble, winning a race, acing a test, doing cocaine or methamphetamines, smoking, drinking. (Emphasis mine.)

This description of the action of dopamine is wrong for two reasons.

1) A nitpicky point: How the reward system works in drug users and how it works for say shopping or french fries are two very different things.  (I wrote about how sugar is not quite like a drug here.)  There is a world of difference between cocaine and methamphetamines and acing a test. 

Think of it this way.  Many drugs -- not all drugs...some work in different ways -- function to short-circuit the reward system and create the perception of reward in the absence of any tangible rewarding stimuli.  Thus, french fries activate the reward system because they taste good.  Heroin activates the reward system by directly floating into the brain and activating it.  This would explain why heroin is more rewarding (at least initially) than french fries. 

I think putting all of those things in one sentence as if they were equivalent rewards dangerously confuses the complexity of their different functions.

2) This notion of cascading increases of dopamine release as the result of a reward stimuli is just flat out wrong.  That is not how dopamine works at all.

Dopamine is released by what neuroscientists call reward error.  Reward error is a difference between what you the reward you expected to receive and the reward you actually received.  Dopamine is only released in the presence of unpredicted rewards, not repeated rewards.  Further, the dopamine release is lessened if an expected reward is omitted. 

Basically if I give you a cookie that you didn't expect one morning, you are like "Nice!  Free cookie."  You release dopamine.  In contrast, if I give you a cookie every morning for several weeks, this cookie has become a predicted reward; hence there is no further release of dopamine.  (Why this is I will explain in a second.)  Dopamine release would change if you expected to get a cookie every morning and I didn't give you one.  This would be an omitted expected reward, and it would cause a reduction in dopamine release.

The reason that dopamine functions in this way is because it trains your behavioral responses.  This is a point that Skloot does make in her article.  The dopamine is released in areas of the brain such as the striatum and frontal cortex that function in decision making.  The computation that these regions make is that whatever the activity was when the dopamine was released, well, let's do more of that because it was rewarding.  Whatever you are doing when the dopamine was released, let's do that again. 

However, it is important to note that once this behavior has been consolidated, there is no more need for dopamine release.  To use a metaphor, think of dopamine as the means of digging yourself into a behavioral rut.  After the digging is done, you are in the rut.  No more digging is required. 

In addition, Skloot makes light of the significance of predictors of reward, so-called "salient" cues.  It is true that you can condition dopamine release if you show someone a predictor of reward.  The example she uses is being in a supermarket making you think of junk food.  The supermarket is not in and of itself rewarding; it is just associated with junk food.  Therefore, the cue -- the supermarket -- can ellicit dopamine release.  However, cues associated with dopamine release also have a similar period of attenuation:  after a while the cue does not cause dopamine release either.

If you don't believe me about this or would like further reading, I urge to read this paper by Wolfram Schultz who is one of the experts in this field.  To summarize what I have argued, here is a quote from his paper:

Dopamine neurons report rewards relative to their prediction rather than signaling primary rewards unconditionally...The dopamine response is positive (activation) when primary rewards occur without being predicted. The response is nil when rewards occur as predicted. The response is negative (depression) when predicted rewards are omitted. Thus dopamine neurons report primary rewards according to the difference between the occurrence and the prediction of reward, which can be termed an error in the prediction of reward

What makes you repeat behaviors is not repeated dopamine release.  It is the changed activity in the brain regions that facilitate decision making as a consequence of dopamine action. 

Getting back to the focus of Skloot's article -- which I didn't think was half-bad minus that error -- why do we have trouble changing our bad habits?  The problem is not that dopamine is being constantly released.  Rather, it is a problem of getting past the behavioral inertia of the bad habit and replacing it with a good habit.  Later in her article, she mentions research about habitual behavior, and how repitition can consolidate these habits.  She suggests that if you did something for three weeks -- such as exercise, you can make a habit of it.  

This is accurate.  Old habits can be overcome.  What must often be replaced are the cues for bad habits.  This is why we tell former drug-users to avoid their old friends and sometimes move to a different state.  What also must happen is that you have to suffer through a couple weeks of not being happy.