Dr. Dodes recent article, apparently trying to blow up the myth of addiction as a neurophysiological disorder, sounded persuasive, although its underpinning was oversimplified and it's understanding of the brain-science involved in addiction, and other associated mental health disorders, was lacking. Hopefully, by presenting a more complete picture of the evidence for a brain-aspect to addiction, I can un-bias the discussion somewhat.
I, for one, don't believe that neuroscience will ever be the only factor important in addiction - an individual's environment, social influences, and other factors will always end up playing important parts as well - still, I think that to dismiss all of the evidence for biological factors at play in the development of addiction is foolhardy. Especially when there's so much of it that was glossed over in Dr. Dodes' introduction.
Pleasure center activation is only part of the picture in addiction
Firstly, supporters of the notion that addiction is, at least partly, an outcome of specific brain function point not only to pleasure center activation, but also to a whole host of findings showing genetic variability that is either protective from, or a risk factor for, dependence on drugs and likely also behavioral addiction like eating disorders, compulsive gambling, and maybe sex addiction as well (you can start out looking up ALDH2-2 variability and alcoholism and cocaine addiction, DRD4 and stimulant addiction, and many more).
While it is true that all those who consume addictive substance activate the brain similarly, there are considerable differences in the specific of that activation in reaction to drugs. Some release more dopamine while others have more "active" versions of specific important receptors; neurotransmitter recycling is quick in some, but not all, and drug metabolism is different in different individuals in ways that have been shown to be important not just for addiction risk, but also for the probability of treatment success. Just look at the nicotine and CPY26 literature for an example. It's right there.
Additionally an entire body of literature exists that shows differential activation, as well as structural differences, between addicts and non-addicts in regions as varied as the OFC, PFC, Insula, and more. This is not to mention a slew of evidence that shows different behavioral test performance on risk-taking, impulsivity, and delay-discounting, all personality variables highly associated with addiction. If one simply ignore all of this evidence, it may be easy to believe that there is no biological explanation for these phenomena, but that's just wrong.
To say that mesolimbic activation (what the good doctor called "pleasure centers") is the only evidence for physiological factors in addiction is dismissive at best.
Drug addiction develops in only some drug users
The notion that not everyone who takes drugs becomes addicted is nothing close to evidence against a brain explanation for addiction. Everyone's motor--cortex, striatum, and substantia nigra (the areas of the brain responsible for movement) activate in the same way during movement, but only a small group ends up suffering from Parkinson's or Huntington's disorders. One fact does not preclude the other but instead may specifically point to the fact the group which develops the disorder has somewhat different neurological functioning. Researchers aren't concerned with explaining why all individuals can become addicted to drugs, but rather why that small subgroup develops compulsive behavior. A short reading of the literature makes that fact pretty clear. Additionally, while Dr. Dodes' claims otherwise, imaging technology HAS produced evidence explaining this "mystery", including differences in the ways addicted smokers respond to smoking-related triggers, and an increased dopamine response in cocaine addicts to cues, and well as to cocaine.
As mentioned in the motor disorder section above, ingestion of chemicals is not at all necessary for brain disorders to occur or indeed develop later in life. Dr. Dodes example of shifting addiction could be used as evidence for an underlying neurological difference just as well as it would serve to make his point... Or even better. If there's a faulty basic mechanism attached to rewarding behaviors, it doesn't really matter what the behavior is, does it? Sex addiction, gambling, and more can all be explained using a similar mechanism, though drugs of abuse may just have a more direct impact. I know, I've written about them all.
