“CHICAGO -— Young adults who used marijuana only recreationally showed significant abnormalities in two key brain regions that are important in emotion and motivation, scientists report. The study was a collaboration between Northwestern Medicine® and Massachusetts General Hospital/Harvard Medical School.
This is the first study to show casual use of marijuana is related to major brain changes. It showed the degree of brain abnormalities in these regions is directly related to the number of joints a person smoked per week. The more joints a person smoked, the more abnormal the shape, volume and density of the brain regions.”
“It may be that we’re seeing a type of drug learning in the brain,” Gilman said. “We think when people are in the process of becoming addicted, their brains form these new connections.”
In animals, these new connections indicate the brain is adapting to the unnatural level of reward and stimulation from marijuana. These connections make other natural rewards less satisfying.”http://www.northwestern.edu/newscenter/stories/2014/04/casual-marijuana-use-linked-to-brain-abnormalities-in-students.html
But they'll still get it and smoke it and there's nothing anyone can realistic do to stop it.
For one thing, the n sample size is too small to be confident of conclusions. Since this is a non-interventional approach, and no harm to subjects comes about, a larger study using hundreds of subjects is needed. A second criticism involves the self-statements of the subjects as to how often they smoked, which was seen to correlate with degree of "abnormality". This is likely to be wildly variable in reality and some subjects have reasons to not give correct answers, yet the amount of smoking was found to predict abnormality by degree very nicely, in a manner which seems a little too good to be true, especially in such a small study. A third criticism is that no functional description is tied to the abnormal brain structures, other than the rather large leap to the animal study and the conclusion about diminishing efficacy of natural reward. No test scores, etc. Individual brains vary a lot from one person to another. It is conceivable that the "abnormality" could even be superior in some way, if it in fact exists as a result of the THC ingestion.
My impression is that these neuroscientists (a field in which I was trained also) went into the study to prove something and By God did they ever find what they were looking for! Maybe a little too enthusiastically. We will have to wait for future larger, longitudinal, and function-measuring studies to clarify the real cause and effect involved here, and if the "abnormalities" are found reliably and even matter.