Addicted Brains

A neuroscientist examines life on drugs.

When the Thrill is Gone: Reward Deficiency Syndrome

Not enough dopamine receptors? Then you might just want to get high.

Click here and watch a minute or two of B. B. King singing "The Thrill is Gone." You might notice that he does not look happy. Nor does he sound happy. And he's sweating. A lot. He says he's free, but I somehow doubt it.

What happens when the thrill is gone? In fact, what if the thrill was never there to begin with?

I said I'd report to you on everything I learned at the conference on behavioral addictions in Budapest. Well, on day 2 of the conference, I met the guy who coined the term Reward Deficiency Syndrome (RDS). His name is Kenneth Blum. He's a smallish wiry guy, very intense, seemingly dour, but flashing the occasional dry smile. Here's his hypothesis:

When we do whatever it is we're addicted to (substances OR behaviors), the brain systems that "light up" include dopamine circuits in the nucleus accumbens and its neighbors in the prefrontal cortex and motor system. No surprise there. Blum lists half a dozen dopamine receptors that get in on the act. But the prize goes to the D2 receptor. The D2 receptor is involved in attention, motor control, motivation....lots of important stuff. Here's a detailed description. So what happens when the D2 receptor population isn't quite normal (e.g., too many or too few)? What happens is that you are more likely to suffer from a whole host of things, including OCD, ADHD, schizophrenia, and -- you guessed it -- addiction. Addiction to drugs, booze, gambling -- that receptor can be a gateway to the underworld of the psyche.

The problem is that the DRD2 gene, which is responsible for growing D2 receptors while we're still in the womb, has got different variants (like many genes), and one of those variants (allele A1) causes an overall reduction in the number of D2 receptors. There's lots of evidence that addiction runs in families. I usually steer away from that side of things and focus more on experience -- nurture, not nature. But Blum cites some pretty convincing research showing that addictions shared across generations (like father, like son) correspond with this nasty dopamine allele. In other words, the allele gets passed down to the same offspring who end up becoming addicts.

Now some people have fewer D2 receptors than the general population, like maybe 40% fewer in some brain areas like the nucleus accumbens. So these people are not as excited about reaching their goals. Their whole "reward system" is relatively flat. Life is not as much of a buzz for them as it is for most people. As with B. B. King, the thrill is gone. In fact, maybe it was never there at all.

If you have the wrong allele of the DRD2 gene, and thus
fewer D2 receptors, you're slated for RDS. So how are you going to get the thrills those around you seem to get? Well, drugs (including alcohol), gambling, and other super-fun stuff might be the most effective way. These "rewards" are hyper-exciting for most people. For you, who are chronically under-excited, they might be the only way to feel really engaged with life. Addiction, then, is just an unfortunate side-effect.

That's the story, according to Blum. Reward deficiency leads you to seek out the biggest bang for your buck. Which makes sense, because everyone wants to feel the excitement that dopamine

bestows when something special is about to happen. When I was a kid, about age eight or so, I remember making a disturbing discovery. Almost all the fun I had in life seemed to come with looking forward to things, whether a chocolate bar or a birthday present. Once the desired event was actually happening, it wasn't as much fun anymore. (I was a weird kid, no doubt.) But for most people, a lot of pleasure comes from anticipation, from approach, and that's what gets muted with RDS.

Despite its appeal, there are some serious problems with the RDS model. I'll name just two. We know from dozens of studies that drug or alcohol use itself leads to a reduction in dopamine receptor density, or at least dopamine receptor activation, because those receptors tend to burn out or become desensitized when we keep bombarding them with fun stuff. Now that's getting closer to B. B. King's complaint: The thrill was there for awhile, but now it's gone. The question remains: is your dopamine landscape more determined by your genes or by how you use them? Problem #2 is that teenagers as a group are often described in terms of reward deficiency syndrome. Teens can be seen as under-stimulated, probably because the reorganization of the nervous system in adolescence is pretty uneven, with new motives often preceding new opportunities for fulfilling them.

So teenage thrill-seeking is not only natural, it's inevitable. Unfortunately, dangerous drugs are often part of the picnic. In other words, genetic contributions to addiction may simply be dwarfed by a tidal wave of thrill-seeking that comes with adolescence.

The jury is still out when it comes to genetic influences on addiction. Few addiction researchers doubt that such influences exist, but their exact mechanisms aren't well understood. Blum and his colleagues are still chasing down the RDS model, and trying to connect it to other influential models, like Berridge's incentive sensitization model. There's still a lot to learn.

Marc Lewis, PhD has been a professor of developmental psychology and neuroscience for over 20 years and is the author of Memoirs of an Addicted Brain. 

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