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"...