thoughts on these two studies?

My 2 cents - these are competently executed studies, but like anything else, you have to take them with a grain of salt. The first study is cross-sectional. Is it marijuana use that is associated with the impaired axonal connectivity, is it impaired axonal connectivity that is associated with marijuana use, or is it something else all together that is associated with both?

The findings of the second study appeared more robust at first as it made us of multiwave data, however, their conclusions were based on psychometric assessments (one of my areas of specialization) as opposed to MRIs. One things to consider is as follows: does marijuana use exert a temporary influence on test scores or does it actually influence the neurological structures associated with scores on those tests? My presumption is the former and unfortunately, this study cannot tease these two explanations apart.

Also consider that none of these studies make use of random assignment (which would be unethical and infeasible in this situation). Really, studies along these lines need to be conducted with mice using MRIs (or sacrificing the animals to examine their brain structures) in order to actually answer these questions.

Make no mistake about it, these are both good pieces of science. But like any study, they really raise more questions than answers.

Note that my PhD is in the social sciences rather than medical sciences, so you can take my comments with a grain of salt. Also note that I did not thoroughly read these papers, but simply skimmed them.

Glad to see someone from the same line of work around these parts. Welcome to fc! A very good breakdown of the limitations of the study

Like I said earlier in this thread, a lot of the limitations of these studies are due to the limitations of the conventional psychometrics used in these studies.

I do agree that we need to be looking for more direct indicators, and rethinking our methods in general - rather than the somewhat conceptually shakey methods that often get used within our discipline/s. IQ should be abandoned though, a psychological construct that is meant to represent another psychological construct (the concept of intelligence) is not good science in my humble opinion. We need to get back into the real world, remember that these concepts are only useful when they are clearly defined and understood - and even so, measuring with these concepts remains a tenuous exercise. We have conceptual work to do before studies like these are worth undertaking. We need to ask: what is intelligence (and not just a circular operational definition ie: 'intelligence is what intelligence is purported to do')? We need to establish whether intelligence is a 'thing' to be measured, amongst many other crucial questions.

Apologies for what was probably a very jargon-loaded post, but I am passionate on this topic lol

I am a psycho-educational specialist with years of practical experience in the education field, and my bottom-line 2-cents on the matter is this: the measurement of intelligence cannot be ascertained by the all-too-numerous IQ tests, which attempt at great variance among them, to measure and define 'capacity' and 'application'. It is, that is - 'intelligence' - is much too fluid and fleeting in nature given immediate personal circumstance, condition, etc., to measure with any degree of accuracy and validity pertaining to long-term implications. It is a moving target ever changing in all shape and substance, expanding and contracting, static at times and racing at others. And by 'intelligence' do we mean to define and isolate it's relevance within the realm of 'emotion', calculation, reasoning, artistic, abstract, concrete, flexibility, ...what exactly, or even what in the most blurred of definitions? I have taught children with severe deficits of all manner and affliction, and they all show extraordinary capacity in one wonderful form or another, in countless kaleidoscopic ways! I say FUCK trying to nail down IQ to the thousandth's degree, and simply appreciate the infinite talents among us in all capacities. Why think in terms of quantifying limitations? Edit: I have a 23 year old cat who's emotional/perceptive intelligence far exceeds just about any human I have ever known, and that's no lie!!!

Enjoyed @Caligula 's comments in this thread, lol

As I said above, If we/anyone takes their DATA, and their assertion, at face value, we are left with a very small study that is inconclusive. But fuck face value.

1) Smoke is a known neurotoxin. This study said "Users smoked a significantly greater amount of tobacco than non-users but did not differ in levels of alcohol consumption." Is it possible that all that smoke had something to do with it? They used regression to determine that tobacco use was not a "significant regressors", but that doesn't explain how toxic smoke would have played in.

2) Another study done at UCSD found conflicting results. "Marijuana use during the interscan interval did not predict change over time."
http://onlinelibrary.wiley.com/doi/10.1111/j.1530-0277.2012.01920.x/abstract
(Might even help protect the brain slightly from binge drinking damage)

3) Setting smoke and a contradictory study aside, how would quality of cannabis factor in? All I know about Aus. cannabis is there are two types. The brick stuff and another commonly available type which I hear is decent, but nothing great and nobody is quite sure where it comes from. These are just what I've heard from a number of people. May not be true at all. I am sure that SoCal has access to "medical" (quotes due to differences in that claim) strains that are considered to be some of the best in the world.

Sorry for the ramble, but since both studies contradict each other, the quality of cannabis would seem to play an important part. Organic, well tended, lab tested product, would seem to be far less detrimental than something with unknown amounts of pesticides etc.

4) There is no behavior endpoint. It is possible that the "axonal fibre connectivity" precedes the cannabis use. Are there any negative effects?

Those are the 4 main ones that jump out to me. I also wonder how cannabis can be both a neuroprotectant and neurotoxin? If the cannabinoid receptors are more concentrated in white matter, wouldn't an increase be beneficial to some degree? Is it possible there is a reduction in pathways due to others being more effective? How many "users" out of 59 would have to not abstain for the requested 12hr period before a scan to skew the results / not abuse other drugs?

I've seen a lot of comments in this thread, but none that have convinced me that either of these studies have any validity to their assertions. The above can all be argued against. Just some observations from a non scientist.

Their assertion that "Our findings indicate long-term cannabis use is hazardous to the white matter of the developing brain." is false. Even if cannabis really is the cause of a change in axonal streamline pathology, there is no evidence of a hazard/danger due to a decrease in streamlines. Just reacting differently.

The assertion is false, the methodology is flawed, and if anyone can show how this study has any validity beyond the "we need more research" line, I'd love to hear it. Until then, this is just another meaningless study in a long line that I'm waiting to see replicated.

Magic9 said:

Smoke is a known neurotoxin.
I also wonder how cannabis can be both a neuroprotectant and neurotoxin?

Click to expand...

Great analysis
Combusted cannabis causes smoke, so smoked cannabis is a neurotoxin.
Cannabis ingested in other ways is a neuroprotectant.