For people who like both Science and Chocolate - a big post on chocolate in Cocktail Party Physics: [link]
Apparently there's been lots o' scientific research on cocoa in the last ten years....
There's quite a few chemical components to cocoa. First, there's the so-called methylxanthines: caffeine and theobromine. Then there's biogenic amines like tyramine and tryptamine, as well as the by-now-well-known cocoa flavanols (which I always confuse with flavonoids; flavanols are a subclass of flavonoids, but that's as far as my understanding goes), most notably epicatechin. There's also dopamine-related compounds like salsolinol, and certain endocannabinoids like anandamide. All of these are being studied in one way or another for their potential effects on human health, whether it be measurable, direct psychophysiological effects, or acquired behavioral and psychological effects (which tend to be a bit more subjective).
Fun.
eta:
To sum up:
* The "reward" effect from eating chocolate is largely psychological, because it require consuming huge amounts of the stuff in a single sitting to have a significant chemical effect.
* Ditto for the possibility of chocolate being chemically addictive; the chocoholic phenomenon appears to be largely behavioral/psychological in nature.
* Like any food or beverage containing caffeine (and in the case of cocoa, theobromine as well), chocolate does temporarily increase cognitive or psycho-motor performance.
* The jury is still out, however, on whether consuming a flavanol-rich cocoa drink improves learning, memory or one's ability to perform complex cognitive tasks.
* The single best reason for consuming a flavanol-rich cocoa drink like Cocoapro, despite the bitterness, is that it can have a significant positive effect on cardiovascular health, reducing one's risk of high blood pressure, stroke and diabetes -- particularly for aging individuals.