Checking into the reward pathway in the brain...

There is a reward pathway in the brain.  This is a bundle of dopamine containing neurons.  It goes from a deep area (ventral tegmental) in the brain than up to the prefrontal cortex.  We know that this pathway is activated with any pleasurable activity, including eating (chocolate),and drinking, playing video games, running, making love or other drug induced activity.  With recreational drugs this area of the brain can be stimulated to create a pleasurable buzz to a euphoric high.  In an experiment with rats this area of the brain was stimulated by pushing a lever.  They continued pushing the lever up to 6,000 an hour.  We crave this kind of stimulus. 
Another way of stimulating this pathway is with LENS neurofeedback.  The brain works to get this sort of pleasurable feedback by releasing any of the clogged up areas.  We then have a way of creating natural pleasure without any outside influence.  This has been tested with a mediation group in California.