Aversion and Reward: Brain Pathways and Addiction Treatment

By Regina Walker 10/27/15

It’s becoming increasingly clear that our whole understanding of what addiction is, and how to treat it, will be revolutionized.

Too Close For Comfort

Deep inside your brain are two small clusters of nerve cells, roughly the size of a walnut. (The brain, like the body, is symmetrical; it’s pretty much the same on one side as the other.) Brain scientists call these little knots of cells “nuclei” (just one is called a nucleus) and each tends to have a certain special job to do. Right now, we’re interested in one called the nucleus accumbens. (Well, two really; remember, in the brain as in the rest of the body everything comes in pairs.)

The nucleus accumbens' rather funny sounding name is Latin, like so much medical terminology. (This is thanks to the fact that for centuries, Greek and Latin were the languages used by doctors and scientists in Europe; in this case the name means, roughly, “nucleus next to the midline of the brain.”) It may have a weird-sounding name and not sound very impressive in terms of size, but that little knot of brain cells at the base of your brain has a big job: making sure you do what you need to, to stay alive.

We’ve talked about this before on The Fix, but let’s get into the subject a little deeper now. We like to think of ourselves as thinking animals, who do things for a reason—and it’s true that we are, and do—at least some of the time. But on a deeper level, we do things for emotional reasons—simply put, we like to do things that feel good, and we hate doing things that feel bad. Now things that feel good, don’t feel good without reason. Water and food taste good to us because if they didn’t, we wouldn’t drink or eat and we would not be motivated to do what we need to, to get food and water. Sex, as you probably don’t need to be told, feels pretty terrific, and that’s because if it didn’t, we wouldn’t be strongly motivated to try and make it happen, and after a while, there wouldn’t be any people around.

It doesn’t just stop with momentary pleasure, either. The nucleus accumbens is part of a whole system of connected pathways and nuclei in the brain that, all together, make up what brain scientists call the reward-aversion system. The whole job of the reward system is to make sure you do whatever you need to, to survive and reproduce. The job of the aversion system is to make sure you don’t do anything that will get you killed. These two systems work together, by “talking” to other parts of the brain that influence emotions, and that are involved in making long-range plans. So we don’t just feel that something feels good, and leave it at that. We’re actually wired to make plans to do the thing we just did that was fun, at some point in the future as well.

The aversion system does the same thing, but with the opposite effect. The classic example of an aversion response is how we react to the smell of rotten meat. The reaction is very powerful; you would have to work pretty hard to overcome it. And once again, the reaction is an emotional one; the meat smells bad. Some kinds of aversion seem to be innate, but others can be learned.  

The classic study that really marked the beginning of our understanding that there was a neurological basis to addiction took place in 1954. Two scientists—James Olds and Peter Milner—placed electrodes in the region of rat brains in which the nucleus accumbens is found. (In many respects, all mammals share the same basic brain structure.) They found, much to their amazement, that a low voltage electrical current applied to this part of the brain acted as a powerful reward, and that rats who got a trickle of current in a certain part of a maze would return to that part of the maze again and again. They had been, as psychologists and psychiatrists say, “conditioned.” Olds and Milner subsequently found that rats would push a lever that gave them a burst of current—and thus, pleasure—again and again, forgetting to eat or even drink: the very model of addiction. Their study was published as “Positive Reinforcement Produced By Electrical Stimulation of Septal Area And Other Regions Of The Brain.” (The study, by the way, also influenced science fiction writer Larry Niven, who wrote of a future world where addicts could be found whom he dubbed “wireheads”—people fitted with electrodes that stimulated the pleasure centers; he also wrote of a weapon called a tasp that could stimulate a person’s pleasure centers from a distance so powerfully as to incapacitate them.) 

The problem of course, is that there are unfortunately many things in this world that feel good, but aren’t necessarily good for you, and thus, we have the potential to feel powerfully motivated to do things that might be pleasurable for the moment, but that harm us over the long term. That urge to do things that feel good but hurt us in the long run, is basically all addiction really is. There is an increasingly enormous amount of research that shows that addiction is pretty complicated, at least from a medical and a neurological standpoint—for instance, it’s been observed for many centuries that addiction tends to run in families, and in modern times, it’s become increasingly clear that there is a major genetic component to addiction, but it’s only in the last few years that we’ve started to see how specific genes might increase a person’s vulnerability. We’re also increasingly aware of the role that environment plays—research shows that one of the biggest predictors of addiction is exposure to highly traumatic emotional events, especially in early childhood.  

And, research is also progressing to the point that some of the mysteries around why one treatment works for one person, but might not work for another, have started to unravel a bit.  

One recently published study showed a fascinating, and hitherto unsuspected, potential problem not only in the treatment of addiction, but in the treatment of depression. 

Scientists have long suspected that the two are linked. Both addiction and depression are tied to the nucleus accumbens, and it is also known that depression and addiction are often found together. The details, as you might expect, are complicated, but the basic story is this: the parts of the brain, and specifically of the nucleus accumbens, involved in increased risk of depression and of relapse are affected by the same neurotransmitter. (As you might remember, neurotransmitters are chemicals produced by cells in the brain, to influence other cells, and control brain activity.) 

Stress, for instance, has long been known from observations of the behavior of addicted persons, to be a trigger for relapse; but we can now see exactly which neurotransmitter pathways are affected by stress and how those pathways can trigger the reward-aversion wiring in the nucleus accumbens to drive relapses.

The study looked closely at the exact wiring of the reward-aversion pathways in rats, and discovered an interesting fact: they’re right next to each other; less than a millimeter apart. That means that if you give someone a drug—one intended to help fight an addiction, perhaps, or also one intended to fight depression—that, at least some of the time, the reward pathway gets stimulated at the same time as the aversion pathway, and the two cancel each other out, which means you’d get no effect at all.

The pathways use a type of receptor for neurotransmitters called a kappa opioid receptor. The study’s lead investigator, Dr. Michael Bruchas, explains:

“We studied the neurons that cause activation of kappa opioid receptors, which are involved in every kind of addiction—alcohol, nicotine, cocaine, heroin, methamphetamine,” he said, as reported in the journal Neuron this month. He went on to say; “We produced opposite reward and aversion behaviors by activating neuronal populations located very near one another. This might help explain why drug treatments for addiction don’t always work—they could be working in these two regions at the same time and canceling out any effects.”  

Another researcher involved in the study, Dr. Ream Al-Hasani, said, “We were surprised to see that activation of the same types of receptors on the same types of cells in the same region of the brain could cause different responses. By understanding how these receptors work, we may be able to more specifically target drug therapies to treat conditions linked to reward and aversion responses, such as addiction or depression.”

With such highly focused and detailed studies, it’s becoming increasingly clear that our whole understanding of what addiction is, and how to treat it, will be revolutionized in coming years by research that may finally yield widely effective treatments for one of the oldest, most persistent, and most difficult problems in medicine.

Regina Walker is a regular contributor to The Fix. She last wrote about the role of DBT in the treatment of addiction as well as the ACE test to predict future addiction.

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Regina Walker is a licensed psychotherapist in NYC. She has written for multiple publications and is an avid photographer. You can find her on Linkedin or follow her on Twitter.