November 11, 2014, Los Angeles Times: REGULAR POT SMOKERS HAVE SHRUNKEN BRAINS, STUDY SAYS: “Experimental mice have been telling us this for years, but pot-smoking humans didn’t want to believe it could happen to them: Compared with a person who never smoked marijuana, someone who uses marijuana regularly has, on average, less gray matter in his orbital frontal cortex, a region that is a key node in the brain’s reward, motivation, decision-making and addictive behaviors network. More ambiguously, in regular pot smokers, that region is better connected than it is in non-users: the flow of signal traffic is speedier to other parts of that motivation and decision-making network, including across the superhighway of “white matter” that connects the brain’s hemispheres.”
There has been much speculation on this fundamental issue but it is not surprising to me because we seem to easily forget the impact of chronic alcohol intake on brain function (se:https://en.wikipedia.org/wiki/Wernicke%27s_encephalopathy). Excess has its costs, so how do we determine just the right amount of alcohol or pot that is safe. I suspect that it is different between people, some get these problems with lesser dosages.