Considering how many people fall prey to addiction, and considering how many potentially addictive things are in the world — including food we eat every day — it might seem as if science should know a little more about it by now. But many questions are open, and Bethany Brookshire lists some of them. A human is wired to have a reward system, which is meant to encourage us to continue doing and pursuing things that are good for us. But sometimes the reward system gets its wires crossed and causes us to want things that are bad for us. Is that the root of all addiction?
Or is addiction basically a learning disorder? Or an inappropriate overreaction to normal stress that most people develop healthier ways of dealing with? Or does it stem from an unlucky combination of inborn genetic conditions that interact badly with input from the environment? Brookshire suggests that while none of those ideas are wrong, they are all incomplete:
Addiction is a disorder of reward, a disorder of learning. It has genetic, epigenetic and environmental influences. It is all of that and more. Addiction is a display of the brain’s astounding ability to change — a feature called plasticity — and it showcases what we know and don’t yet know about how brains adapt to all that we throw at them.
While a case can be made that genetic differences cause some individuals to have an increased vulnerability and propensity toward addiction, that is only a small part of the total picture. And while dopamine does undeniably play a role, it turns out not to act in the ways that were originally assumed to be the totality of the picture. Different areas of the brain don’t always connect in the same ways. Neither the chemicals nor the receptors consistently act in the ways that researchers had come to expect. Many times, causality is an open question.
The trouble with studying the brain of an addict is the difficulty of distinguishing what conditions existed there before the addiction. What came first? Some sort of deficit that opened the door for addiction? Or a continuing assault upon the system by some substance, which created a deficit?
Science thought for a while that the answer could be found in dopamine, the brain chemical associated with pleasure. Addictive drugs bring out more of it. But that simple theory has been thrown into doubt.
Paul Kenny, a neurobiologist interviewed by the writer, notes a subtle but significant difference — the notion that dopamine measures not pleasure, but value. For instance, the presence of a drug has the effect of re-prioritizing the reward system. The substance is assigned the highest value, while other parts of life such as family, money, work, and law-abidingness take a back seat. Brookshire explains:
As someone takes a drug over and over, dopamine and other systems in the brain respond with plasticity — that is, those systems adapt to the presence of the drug. Receptors that control the response to chemicals like dopamine change concentration. Connections between brain cells and between different areas of the brain strengthen and weaken.
As Dr. Kenny admitted, “Now, scientists are willing to admit we have no idea where reward comes from or how we experience pleasure.” So, back to square one.
To many researchers, it appears evident that all behavioral disorders are the same because they all involve learning and plasticity. One example given is the development of habits, which generally benefit us. It’s a very good thing that a person can, for instance, remember how to use a toilet even when half-asleep, in pain, or just preoccupied with other thoughts. If we had to stop and relearn how to do it every time, life would be complicated indeed. Most of our habits are good. But when an addictive substance is present, the brain learns differently and in maladaptive ways. We not only catch bad habits, but the process of habit formation gets speeded up.
Brookshire’s article of course goes into much greater detail about all these ideas and the researchers who discuss them. She wraps it up with a comprehensive back-to square-one type of statement:
The only overall explanation for addiction is that the brain is adapting to its environment. This plasticity takes place on many levels and impacts many behaviors, whether it is learning, reward or emotional processing. If the question is how we should think of addiction, the answer is from every angle possible.
Your responses and feedback are welcome!
Source: “Addiction showcases the brain’s flexibility,” ScienceNews.org, 08/05/14
Image by torbakhopper