Sunday, January 27, 2013

Weed or Wheel!

Research Article: Weed or Wheel! fMRI, Behavioural, and Toxicological Investigations of How Cannabis Smoking Affects Skills Necessary for Driving


Article here.  Abstract:
Battistella G, Fornari E, Thomas A, Mall J-F, Chtioui H, et al. (2013) Weed or Wheel! fMRI, Behavioural, and Toxicological Investigations of How Cannabis Smoking Affects Skills Necessary for Driving. PLoS ONE 8(1): e52545. doi:10.1371/journal.pone.0052545
Marijuana is the most widely used illicit drug, however its effects on cognitive functions underling safe driving remain mostly unexplored. Our goal was to evaluate the impact of cannabis on the driving ability of occasional smokers, by investigating changes in the brain network involved in a tracking task. The subject characteristics, the percentage of Δ9-Tetrahydrocannabinol in the joint, and the inhaled dose were in accordance with real-life conditions. Thirty-one male volunteers were enrolled in this study that includes clinical and toxicological aspects together with functional magnetic resonance imaging of the brain and measurements of psychomotor skills. The fMRI paradigm was based on a visuo-motor tracking task, alternating active tracking blocks with passive tracking viewing and rest condition. We show that cannabis smoking, even at low Δ9-Tetrahydrocannabinol blood concentrations, decreases psychomotor skills and alters the activity of the brain networks involved in cognition. The relative decrease of Blood Oxygen Level Dependent response (BOLD) after cannabis smoking in the anterior insula, dorsomedial thalamus, and striatum compared to placebo smoking suggests an alteration of the network involved in saliency detection. In addition, the decrease of BOLD response in the right superior parietal cortex and in the dorsolateral prefrontal cortex indicates the involvement of the Control Executive network known to operate once the saliencies are identified. Furthermore, cannabis increases activity in the rostral anterior cingulate cortex and ventromedial prefrontal cortices, suggesting an increase in self-oriented mental activity. Subjects are more attracted by intrapersonal stimuli (“self”) and fail to attend to task performance, leading to an insufficient allocation of task-oriented resources and to sub-optimal performance. These effects correlate with the subjective feeling of confusion rather than with the blood level of Δ9-Tetrahydrocannabinol. These findings bolster the zero-tolerance policy adopted in several countries that prohibits the presence of any amount of drugs in blood while driving. 


This article recently caught my eye, and it's pissing me off. Mind you, I don't think PLOS One is the most reputable of sources, but this may not be known beyond academic circles, and any policy-maker will be happy to choose this article over another that may be more difficult to access or extract a message from. And therein lies the problem: It's not that the article is bad, per se. The rationale seems sound, the methodology is acceptable, even the results are fine. What's rubbing me the wrong way is the obvious political agenda, and the way it is snuck into the interpretation and discussion -- and undeservedly so. The sweeping, politically charged conclusions are not at all supported by the data, so even though the data themselves are fine, this kind of aggrandization is dangerous in my opinion. I'm surprised to see this coming out of Europe, where I like to tell myself they're more enlightened about drug research. Sigh.

So let's start with the results. In a nutshell, the investigators had subjects smoke pot vs. a placebo joint, and perform an out-of-scanner object tracking task that has shown some relationship to real-life driving, an in-scanner tracking task while brain activity was measured with functional MRI, and self-reports of high, confusion, confidence in ability to drive, etc. Self-reported effects went as expected after pot compared to placebo, and performance on the tracking tasks decreased. During the in-scanner task, a lot of brain regions predictably involved in task performance showed lower activity after pot vs placebo, and a few showed higher activity. And in some of those regions, activity correlated with self-reported confusion. I may have missed a few, but that's the basic gist of it.

The point of contention is with the statements they make in the interpretation of the data. The abstract alone (which, presumably, is all a policy-maker will read before making a decision) feels like a heap of half-truths and manipulation.
"Our goal was to evaluate the impact of cannabis on the driving ability of occasional smokers, by investigating changes in the brain network involved in a tracking task." I don't think this is a fair description of the rationale for the study. They may well have wanted to investigate the effects of cannabis on brain networks involved in a tracking task, but everything in between is pure conjecture. We don't know if the tracking task has ANYTHING to do with driving ability, in the absence of a test that involves.....actual driving. The out-of-scanner tracking task they use has a "moderate correlation with real-world driving," but that's not the one that was used in the scanner, and they never test if performance on the two tasks correlates with each other, let alone actual driving.
"We show that cannabis smoking, even at low Δ9-Tetrahydrocannabinol blood concentrations, decreases psychomotor skills and alters the activity of the brain networks involved in cognition." This statement isn't entirely unfair, but I don't see how it deserves to be applied specifically to driving. The evidence suggests that subjects were feeling more generally "confused" after cannabis, which could also impair their ability to walk on a crowded sidewalk, or mow their lawn, or play chess. Why isn't the article focused on those?
"Subjects are more attracted by intrapersonal stimuli (“self”) and fail to attend to task performance, leading to an insufficient allocation of task-oriented resources and to sub-optimal performance." This statement is the authors' interpretation based ENTIRELY on the brain regions that were activated/deactivated. But brain regions tend to be involved in more than one thing (including, but far from limited to, the thing that is convenient for the interpreter), and it seems overreaching to make it sound like a sure result in the absence of having tested any of these things.
"These findings bolster the zero-tolerance policy adopted in several countries that prohibits the presence of any amount of drugs in blood while driving." This is the one that got me. I mean, what?! Until someone gets a research subject high and puts them in a driving simulator, this is a HUGE leap in logic. How does decreased performance on an in-scanner tracking task translate to real-world driving behaviour? It can't be the only factor that goes into driving, and maybe people can recruit other resources to compensate for impairment when their safety is actually on the line, and just as there is a low blood alcohol level that is considered "safe" for the roads (but surely impairs task performance too), shouldn't it be tested if there is a dose-response relationship for cannabis too before calling for a zero tolerance policy? (I mean, don't get me wrong, I am NOT in favour of impaired driving, and firmly believe that no one has the right to make their intoxication anybody else's problem. But I am equally not in favour of skewed statements with little basis. If you're going to broadcast claims to the world, they should at least be backed up.)

Also, I find the conclusion of the manuscript entirely schizophrenic: "...we failed to find any quantitative correlation between the THC levels measured in whole blood and either the BOLD signal or the psychomotor performance. These results bolster the “zero tolerance policy” that prohibits the presence of any amount of THC in the blood while driving." If self-reported confusion correlated with outcome measures, but THC in the system didn't.....wouldn't it make more sense to call for a zero tolerance policy on confusion?

In all seriousness, though, the paper certainly deserves a spot in the Journal of Proofs of Concept with Potential Implications for the Real World; it's not groundbreaking, but it IS the sort of thing that policies should be built on. But to scoop up a bucket of sand and call it a sandcastle is not just unprofessional, but in this case, potentially detrimental to evidence-based policy progress.

2 comments:

  1. I don't know if you have ever met or heard of Dan O'Leary at the University of Iowa, but he's done a bunch of interesting Marijuana studies with FMRI. I've not read them all but I've been to some of his whiteboard talks and he seems like he is very focused on coming up with interesting results without editorializing. One funny thing he once said in a meeting was "Iowa is great for Cannibis research because we seem to have a sizeable population of regular users who don't use any other illicit drug."

    Iowa also has a gazillion dollar driving simulator where they could do actual testing of driving response while under the influence, in fact they seem to be recruiting subjects here: http://www.drivingstudies.com/

    The anecdotal evidence (i.e. talking to people who smoke pot) is that it does not impair driving the way alcohol does, unless you're really really high. And combining alcohol and weed degrades one's driving ability more than either by itself.

    Even if this anecdotal conclusion is borne out by actual research, it raises interesting questions: If it is possible to get high enough to impair driving on par with significant blood alcohol levels, are people that stoned less likely to try and drive? My instincts say yes -- if one is that messed up, you just want to stay on the couch and wait for the fog to clear. Also, is it possible that the subjectively pleasant dosage of marijuana is less impairing than subjectively pleasant dose of alcohol?

    That would be an interesting study: Have one group smoke to a comfortable high, and test them, then have another group drink until they're pleasantly buzzed and test them.

    And one hazard no one studies with respect to cannabis and driving: The tendency to miss turn offs and/or get lost.

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    1. interesting points, for sure. i'm not sure i agree with a couple of things though:

      i don't think people who are stoned are less likely to want to drive than people who have been drinking. from what i observed while living in car-centric places (detroit, L.A.), people get fucked up, and if they want to get from point A to point B, they get in the car. the end. there is no intervening thought, and no alternative even considered, even if the alternative is sitting on the couch eating cheetos. if you need to be at point B, it's just what you do.

      the other thing is that "subjectively pleasant dose" is sooooo…..well, subjective, and dependent on context, and certainly changes the longer one uses. and with a factor that varies so considerably across people, it's near impossible to come up with a decent standard or limit. also, i think subjective experience should NEVER be a yardstick for ability to drive. people who feel completely sober could have way impaired judgment and motor function, and it's exactly this that's so problematic -- "i feel fine" and "my safe driving capacities are unimpaired" are two completely different things.

      that said though, i do like the idea of leaving it up to the subject to smoke/drink to a comfortable level and go from there….. i just bet it'd be a bitch to get it by journal reviewers.

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