Wall of text inc fellas, btw some more clicks on them you-know-what would be much appreciated.
If you are still wondering whether humans were intended to enjoy and benefit from marijuana's main psychoactive ingredient, THC, pick up a copy of Michael Pollan's bestseller "The Botany of Desire." Pollan, a contributor to The New York Times, should be required reading for anyone weighing the pros and cons of marijuana's booming new acceptance, both as a medicine and perhaps further down the line as a recreational drug. I stumbled across it while researching my own book on medical marijuana, and this is one of the best I've found explaining the drug's affect on the human brain. Most fascinating to me is the revelation that the brain is pre-wired to accept cannabinoids, the active ingredients in cannabis of which THC is one. Just as the brain has receptor cells for endorphins, serotonin and other chemical compounds, so too are there cells specially designed to pair with cannabinoids to unlock certain mental functions.
Here' the gist, in Pollan's words:
In 1988, Allyn Howlett, a researcher at the St. Louis University Medical School, discovered a specific receptor for THC in the brain -- a type of nerve cell that THC binds to like a molecular key in a lock, causing it to activate. Receptor cells form part of a neuronal network; the brain systems involving dopamine, serotonin and the endorphins are three such networks. When a cell in a network is activated by its chemical key, it responds by doing a variety of things: sending a chemical signal to other cells, switching a gene on or off, or becoming more or less active. Depending on the network involved, this process can trigger cognitive, behavioral or psychological changes. Howlett's discovery pointed to the existence of a new network in the brain.
The cannabinoid receptors Howlett found showed up in vast numbers all over the brain (as well as in the immune and reproductive systems) though they were clustered in regions responsible for the mental processes that marijuana is known to alter: the cerebral cortex (the locus of higher-order thought), the hippocampus (memory), the basal ganglia (movement), and the amygdala (emotions). Curiously, the one neurological address where cannabinoid receptors didn't show up was in the brain stem, which regulates involuntary functions such as circulation and respiration. This might explain the remarkably low toxicity of cannabis and the fact that no one is known to have ever died from an overdose.
On the assumption that the human brain would not have evolved a special structure for the express purpose of getting itself high on marijuana, researchers hypothesized that the brain must manufacture its own THC-like chemical for some as-yet-unknown purpose. ... In 1992, some thirty years after his discovery of THC, Raphael Mechoulam (working with a collaborator, William Devane) found it: the brain's own endogenous cannabinoid. He named it "anandamide," from the Sanskrit word for "inner bliss."
So there you have it. Not only is part of the brain designed specifically to react to cannabinoids like THC, but it produces its own in order to achieve effects similar to smoking marijuana, including pain relief, sedation, impairment of short-term memory and cognitive befuddlement. (It should be noted that THC is far stronger and longer-lasting than anandamide, exaggerating and prolonging the effects of the naturally occurring chemical.) Why would the brain want to do this to itself?
Pollan (and the scientists he consulted with) have a few theories, the most intriguing of which is as a natural curative for the "routine slings and arrows of life." Not only is pain dulled (such as during childbirth; there are cannabinoid receptors in the uterus) but quickly forgotten.
Another possibility is that the brain equips us with the natural ability to be amused and excited by our surroundings, that it allows us (through the activation of these cannabinoid receptors) to forget what we know, however mildly, and see the world anew from time to time through the lens of suspended knowledge and rediscovery. As anyone who has ever been high knows, this is one of the main pleasures of the experience -- hearing a song as if for the first time, appreciating textures and colors more fully, being much more intimately aware of one's tactile surroundings.
Such experiences might seem like a waste of time to those who rail against marijuana as the "devil's weed," but evolution apparently considered them valuable enough to develop an entire neural network devoted to their pursuit.
And who's to argue with your own brain?