In my first exposure to Psychology as a course of study, I was a senior in high school. The class was second period, so I had time to come down from my before-school session and actually absorb some information. Psychology was a great class; you learn all about yourself, quantify the differences in personality, and find out people are generally sheep. During my study, I also learned about the importance of your corpus callosum.
That is the bit that connects the two halves of your brain. It is not required for a happy life, but those with a severed corpus callosum — usually due to the treatment of epilepsy — have difficulty with spontaneous speech and listening to commands that require the use of a non-dominant hand.
This classic informational video is a great primer on the subject.
A new study in Psychological Medicine shows that super chronic weed may be doing its part in perpetuating Reefer Madness. While marijuana has been associated with some kind of psychosis by its earliest detractors, it has never been proven nor determined what level of consumption would contribute to the actual brain morphology. Now, it seems high potent weed may be destructive — at least in some respect.
In summary, of the (small number of total) study participants that used high potency cannabis, a degradation of the white matter within the corpus callosum occurred. That means the connection between the two halves of the brain was weakened.
Whether that is going to result in deleterious, split-brain-type effects is yet to be seen. No increase of psychosis was correlated with high-potency smokers, and, in fact, "the effects of potency and frequency were similar in users and in users without psychosis."