Dr. Richard Garey of Tulane University  theorized that the very strong pot people smoke today is causing common reactions nowdays that were rarely seen back in the 60s and 70s when pot was only about one tenth as powerful as it is now. He spoke of how THC stimulates the pleasure centers located in the midbrain. But also located in the midbrain are the violence and unpleasant emotion centers. The stronger pot evidentally causes neural firing (or misfiring) that lights up not only the pleasure centers but nearby violence centers. The MJ user damages feeder cells by thickening the myelin sheaths of those neurons (because THC is fat soluble and myelin sheaths are fatty) and causing fatty blockages in the synaptic gaps. That causes reduced ability to receive any natural highs, makes one emotionally flat and explains in part the amotivational syndrome. One could theorize that huge amounts of THC would be needed to stimulate any pleasure in the advanced user and adjoining areas would get lit up so to speak. Violence could actually trigger a strong response in the pleasure center by stimulating intense neural activity in the midbrain…activity no longer provided by natural highs thanks to damage by marijuana.