Very interesting to see this article from Bernheim and Rangel in December's AER on addiction and decision making. In addition to coming up with a nifty model presenting the notion that drug use among addicts is a "cue-triggered mistake", the authors then expand into policy prescriptions based on their model.
My confusion, however, starts in the abstract: "use among addicts is frequently a mistake" To back this up the authors give us a story about how we can't infer preferences from observed behavior:
There are plainly circumstances in which it makes no sense to infer preferences from choices. For example, American visitors to the U.K. suffer numerous injuries and fatalities because they often look only to the left before stepping into streets, even though they know traffic approaches from the right. One cannot reasonably attribute this to the pleasure of looking left or to masochistic preferences.
Well, sure, the first time you step into the street I could call that a mistake. But someone who keeps getting run over repeatedly has some additional problems. The authors go into a Hedonic Forecasting Mechanism which is disrupted by the addictive substance to skew the perception of the addict that he's going to get much more pleasure from the addictive substance than he actually will.
Another explanation might be that when someone is addicted to a drug they get an abnormal amount of pleasure from it (as opposed to someone who is not addicted) due to the relief from the craving. In that case there is no skewed perception at all. The person is forecasting correctly that he will greatly enjoy getting the monkey off of his back.
This also fits in to what we know about the effects of attentive/reward drugs on neurotransmitter receptors. When your synapse is flooded with a particular neurotransmitter, the neuron can remove some of the receptor sites that neurotransmitter is binding to. In a nutshell, that means that such a neuron is less receptive to that neurotransmitter.
Fewer receptors mean that when you're not on drugs you're actually feeling worse, which is what results in cravings. The choice becomes one of inter-temporal substitution. Drugs now which will have an immediate relief of symptoms and generate direct reward, or abstain, suffer now, and get an indirect reward sometime in the future.
So getting back to this concept of skewed perception, the non addicted user might go from 0-60 on the Hedon-O-Meter, but because of the down-regulation of receptors the addict is starting at a negative value. Suppose that utility is function of the cubed root of opioids:
The non addicted user has a normal level of 0 for opiates and is getting a 'net' utility of 0 from them. Let's say the drug taken increases opiates by a level of 40. The user now gets utility of 3.4. Repeated use, however, down-regulates the opiate receptors so that when the user is not taking drugs, they are experiencing a -20 level of opiates and a utility of -2.7 (withdrawal). This user takes the same dose and moves from -20 to +20, and a utility of +2.7, but the total change in utility is from -2.7 to +2.7, or 5.4 which is greater than 3.4 received by the non-user.
The model of Bernheim and Rangel has recovered addicts (their receptor levels have returned to normal) being stimulated by usage cues (hanging out with drug buddies, Jimmi Hendrix, etc...) activating the motivational circuitry to seek out drugs. I guess so, but maybe the activation is in response to something else. If you buy into the notion that addicts use drugs in response to cravings, it could be that the cues are associated with the craving rather than just the motivation. As any smoker trying to quit will tell you, they start to crave cigarettes when they are presented with smoking cues (usually hanging out in a bar). It makes much more sense that it is the craving that stimulates the motivational behavior rather than the cues alone. Even though the 'underlying preferences' may be to stay clean, the individual experiences disutility from the craving now and is motivated to satisfy it. And if the craving is stopped by using the drug, that's not a mistake, it's the a rational decision to satisfy a craving.