There are many games which rely upon this neurobiological mechanism for their enjoyment, including chess, checkers and so forth, where direct competition further enhances the enjoyment of making a good decision. The fun of a game of chess lies not just in winning the game but in solving the challenging problem of how to beat the other player given the current state of the board, which is why chess puzzles in newspapers and the like enjoy an audience: solving puzzles is inherently enjoyable, if you're sufficiently interested in the kind of puzzle to want to solve it.
Chess is in effect a game which generates puzzles to be solved, and the same is true of a great many hobby games, the relatively complex, decision-focused board games that enjoy a cult following among geeks of all stripes, although these often have other dimensions to their appeal as well.
But there is more to this connection between the decision center and the reward center than solving puzzles. Researchers at Cambridge University (Clark et al, 2009) have shown that even if we fail at an activity, the decision center will release dopamine if it assesses that we nearly won.
In other words, when we come close to triumph, the limbic system spurs us into another attempt. I have called this mechanism grip, and it explains why gambling and certain digital games can be addictive even in the absence of reward schedules.
When a particular game gets the player into a state of wanting "just one more go", it is because of grip: the feeling that one might succeed (or do better) on another attempt fosters the desire to persevere. Slot machines depend upon this for their appeal (if you didn't win with that coin, surely you will have a better chance of winning next time!).
Although related to grind at the neurobiological level, grip is quite distinct in character. Recall that a player who is grinding is repeating the same activities, accumulating an in-game resource. A player caught in grip is also pursuing future reward, but its attainment is uncertain.
A grinding player knows they will eventually collect enough of their resource to win their reward; a player experiencing grip only believes they will eventually win -- which is partly why slot machines are so effective at making money for casinos.
As it happens, grind also generates grip. The decision center assesses the future reward -- and this reward will certainly be achieved, the only uncertainty is when. As a result, players caught in grinding often have great difficulty stopping, and if they do manage to stop they remain under the game's spell, and anxiously desire to return to it at the earliest possible moment. Players who tend towards goal-orientation are particularly at risk to both grip and grind, and as a result are more likely to become addicted to a game than a process-oriented player.
I myself tend heavily towards goal-orientation, and as my wife will testify I become terribly addicted to computer role-playing games -- to the extent that nowadays I'm not allowed to play them except under special circumstances (such as I am working on the development of one). While living in Knoxville in 2000, I had terrible insomnia because I was playing Pokémon (Game Freak, 1996), a computer role-playing game about training fantasy creatures.
I was so caught up in the grind of the game's reward structures (i.e. improving the abilities of my pet creatures) that I was in a state of perpetual grip, always wanting to get back so that I could evolve my Bulbasaur or get my Pikachu to just the right state. I spent several hundred hours playing those games that year, and I was by no means the only player to be sucked into the fictional world of Pokémon: the original Game Boy games sold an astonishing 45 million units between them.
In the absence of grind, grip occurs when the player is in pursuit of triumph, which corresponds to a large release of dopamine: the player wants to win, and while they believe they can win, grip will motivate them to continue trying. But in order to produce this potent experience of triumph it is necessary for there to be adversity to overcome.
In games of chance, this can be attained by raising the stakes -- the bigger the risk, the greater the reward -- but in games of competition this is attained by direct conflict. This brings in frustrations (i.e. anger) which are associated with the neurotransmitter norepinephrine. Nicole Lazzaro (2004) has also correctly recognized that difficult puzzles also produce triumph; this appears to be because of the close link between the decision and reward centers of the limbic system we have already seen in connection with grip.
It is also worth briefly noting the role of testosterone in sustaining competitive play. Since the 1970s, testosterone has been connected with persistence and tenacity, and testosterone levels spike when player's triumph over adversity. It is not that high testosterone is a requirement to experience Ekman's fiero, it is that people with high levels of this androgen (male or female -- its effect on behavior is not gender-specific) are more likely to persist against a challenge and thus attain victory (Andrews et al, 1972; Oades 1978; Booth et al, 1989; Mazur et al, 1997). To put this another way: players with high testosterone levels are more susceptible to the grip of an undefeated challenge.
Recall that excitement relates to epinephrine, and that competition can be related to norepinephrine. This makes two of the basic patterns of play correspond with the two sides of the fight-or-flight response, first observed by Walter Cannon in 1929. Anger is the underpinning of the desire to fight, and corresponds to competition, while fear lies beneath the urge to flee, and relates to experiences of vertigo and excitement.
It must be noted, however, that a game of competition need not be angry, and an exciting play experience need not be fearful. A low level of frustration (anger) will not even reach the conscious awareness of a competitive player, and although their neurochemistry is identical, excitement and fear are distinct experiences, with only the latter involving the amygdala, the brain's fear center.
What's more, there is a connection between the chemical correlates of the fight-or-flight response (epinephrine and norepinephrine) and the reward chemical dopamine involved in grip, grind and triumph, since the former two chemicals are synthesized from the latter. In fact, essentially every multi-cellular animal that has evolved since the Cambrian makes use of these three catecholamine chemicals -- from ants to zebras -- although the actual chemistry involved is slightly different in certain cases. The chemicals that support play at the biological level are the same as those involved in the most basic behavioral mechanisms of reward and survival.