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.
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.