The marijuana experience -- or the psychedelic experience, in general -- is not simply an experience of the brain, but an activation of the entire nervous system, of which the brain is merely a part. Granted, this activation of the perceptual system of the brain is mostly what we consider when we consider being high, the "buzz" sensation is, at its core, one of the nervous system of the body; a resonant sensation of the in the cyclical electro-chemical state expressed in the action potential of those circuits of nerve cells. Charged! Fully primed! And ready to sense! ...everything!
This flood of the perceptual system is a rush, with subtle aspects of our surroundings, those we do not usually notice, suddenly becoming apparent in all their vibrancy and interconnectedness. It is in this flood of stimulation that the practice of meditation, and the capacity of sustained focus, should be considered essential. Without focus, the flood of associated concepts, inspiration, and ideas can be an overwhelming one, as in the low latent inhibition scores of the psychotic (Spitzer, 1997). As if the whole perceptual system is overwhelmed, leaving the victim scatterbrained with loose associations or even totally catatonic; essentially the flood drowns them. As Carson (2011) suggests, a handful of cognitive faculties separate these psychotics from creative geniuses, the measure of one of which is IQ. To have the capacity to parse all of that incoming activating stimulus into an organized understanding of the world (which can then be, more or less, clearly expressed by some medium) is no small mental feat. Likewise, to calm yourself to the level of attention span needed to retain those long delicate though associations could be thought of as high level mental gymnastics, with the creative superstars who can maintain it being something like star athletes of meditation. Carson calls them the "eminent creative achievers" and is able to show, like psychotics, they have a lower LI score -- that is, they have no filter on their perceptual inflow. The flood is coming, whether they can handle it or not; that is the test which separates rockstar professors from neurotic welfare recipients.
At it's core, that flood of nervous activation is what the mystics experienced as a sort of inner radiance, for which words like enlightenment or bliss have been used. Labels aside, this inward visionary experience allows a perspective on self, society, and spirit from which a person can learn a lot.