Gambling on marijuana use makes for bad decisions

I just can’t seem to stay away from the marijuana debate, even given the recent defeat of Proposition 19 that aimed to legalize marijuana in California. This article is a short one, but speaks to some of the cognitive issues associated with marijuana use.

A study (see here) conducted by a Wake Forest University team (Including Doctor Linda Porrino) found that habitual marijuana smokers (those who smoked an average of twice a day for seven years) may be bad at detecting negative outcomes.

The experiment used fMRI scanning technology to examine the brain activity of smokers and controls during the Iowa Gambling Task, which uses four decks of cards. Two of the decks yield large, infrequent, rewards as well as losses. The other two decks yield small, more frequent rewards, and less losses. The first two are considered the “bad” decks, and the latter two the “good” decks, because selecting from the small-gain, small-loss, decks will result in more gain overall. The task is considered a pretty good, if complex, measure of risk-taking, decision making, and loss-discounting.

Marijuana users lose money while controls gainThe take-home result from the study: Not only did marijuana smokers take longer to learn how to maximize their rewards, but their decision-making brain regions seemed to show lower overall responding during the task, meaning they were less active while performing the decisions. And as you can see from the graph on the left, while the controls were able to achieve overall gains, the same was not true for the long-term marijuana users even after 100 repetitions. It seems that marijuana smokers’ brains were not as efficient at detecting losses and responding to them. Maybe that’s why marijuana users are the first to claim that marijuana use has no negative outcomes associated with it…

As usual, it is important to note that since the participants in the study were not randomly assigned to long-term marijuana smoking, it’s impossible to know if these deficits are specifically caused by marijuana use or if they were pre-existing. Nevertheless, these results strongly suggest that individuals who engage in long-term use of marijuana are cognitively distinct from those who don’t. I think that plays into the argument that marijuana legalization would not increase use, because if that’s actually true, then there’s something different about individuals who choose to smoke weed and it is not the legal status that matters. I suspect that in actuality, people who currently choose to smoke marijuana long-term are in fact distinct, in some ways, from some of the people who would take up smoking the stuff if it became legal.


Christopher T. Whitlowa, Anthony Liguoria, L. Brooke Livengooda, Stephanie L. Harta, Becky J. Mussat-Whitlowb, Corey M. Lamborna, Paul J. Laurientic and Linda J. Porrino (2004). Long-term heavy marijuana users make costly decisions on a gambling task. Drug and Alcohol Dependence, 76, 107-111.

The brain after cocaine – White matter damage and addiction treatment

The brain damage left behind after long-term cocaine use can apparently tell us quite a bit about how well a cocaine addict will do in addiction treatment – as long as we assess the right kind of damage.

Different kinds of brain matter

I’ve talked before about the fact that use of cocaine, and other drugs, can bring about long-term changes in the brain that sometimes include the actual destruction of neural pathways. What you may not know is that brain matter consists of several different components including the cell bodies of neurons (known as gray matter) and the tracts of axons that transmit messages across the brain (known as white matter). There are other parts as well, but those are the two important ones to know for this article.

Gray matter is important because brain transmission isn’t possible without a cell body, which is its operations center. But white matter is equally important because without it, the messages don’t get anywhere. It’s like having a telephone without a communication network – The phone can work perfectly and no one will ever hear you speak.

Until recently, it’s been pretty hard to measure the structure of white matter because it consists of very thin bands that twist and turn throughout the brain. But recent advancements in fMRI imaging and analysis have allowed us to look at it by measuring the direction in which water molecules flow through white matter. It’s called DTI (Diffusion Tensor Imaging) and it’s pretty complicated, but all you need to know is that it lets us know a lot about the integrity of axons in the brain.

White matter and cocaine

Use of cocaine has already been shown to cause damage to brain white matter. A recent study conducted at Yale examined whether the degree of damage can tell us anything about how well people will do in addiction treatment. Researchers took 16 participants and gave them a host of tests as well as some brain scans before sending them off to an 8 week treatment program. The addiction treatment utilized was outpatient and provided different individuals with different combinations of CBT, medication (antabuse), individual, and group therapy. At the end of treatment, the number of clean urine tests (out of 56 total tests) was used as a measure of treatment success. The more clean urines, the better, something I think we need to adopt overall instead of the all-or-nothing view that abstinence is the only form of improvement.

The bottom line: Using three different measures, the researchers found that individuals with more damaged white matter provided less clean urines throughout the addiction-treatment period. Another important fact – the damages areas that were found to be associated with treatment success were found all over the brain. Interestingly, brain damage wasn’t associated with the length of drug use, but it may have been associated with the extent of use (in terms of years and amount used), something the researchers didn’t report on.

Brain matter and addiction treatment outcomes

One day, we’ll have a battery of tests that will let us tailor treatment more effectively towards specific addicts. Genetics, brains scans, and more, will be able to tell us where an addict is especially weak so that we can focus on those areas first. Some may need specific help with impulsivity and weakened learning systems whereas others may be better off with treatment that addresses past trauma and an oversensitive stress response system.

As this research shows, brain scans can offer us a glimpse into the aspects of an addict’s brain that have been compromised. But we’re not there yet – right now, all we know is that certain genes, brain function patters, and experiences, are associated with a greater risk for addictive behavior or a lower chance of recovery. Getting better at more specifically tailoring treatment is still a little farther than we’d like.


Jiansong Xu, Elise E DeVito, Patrick D Worhunsky, Kathleen M Carroll, Bruce J Rounsaville & Marc N Potenza (2010). White Matter Integrity is Associated with Treatment Outcome Measures in Cocaine Dependence, Neuropsychopharmacology 35, 1541–1549.