Abstract

Every day is the same for Evan. Evan wakes up around the same time each day, which isn’t hard to do because he rarely leaves the house. When he does leave the house, it is for one of two reasons: to get food or to gamble. Evan gambles twice a day, every day, at the exact same time each day. He walks into the casino – so many options and nothing but time. He sniffs around searching for the perfect game. Perhaps the next press of a lever will be the one that produces the contents of his dreams. He chooses the high-risk machine – he always chooses the high-risk machine. High risk, high reward. He has been losing a lot recently, so a win must be just around the corner. He presses the lever, this is it. He feels so close to winning that he can taste it. Just another second. Nothing, try again. Evan has not won in a very long time. Occasionally he wins something, but he used to win much more often. He used to play more conservatively and at this particular casino, playing conservatively is the optimal strategy. Evan moved on from “playing the odds” to adopting a more high-risk strategy when scientists began injecting Evan with a serotonergic receptor agonist (8-OH-DPAT) that has been shown to contribute to disordered gambling (Grant & Potenza, 2007; Marazziti et al., 2008). Evan is a rat, and may have been one of 32 male Long-Evans rats that were subjects in a study examining the interaction between reinforcement, punishment, and neurochemical manipulations on choice behavior in a “rat gambling task” (Zeeb et al., 2009). In this experiment at the University of British Columbia, rats were placed in an apparatus with four concurrently available machines that dispensed sugar pellets. The machines were different in that they delivered smaller or larger amounts of pellets at varying probabilities and resulted in a punishing time-out period when wins did not occur. The reinforcement and punishment schedules were arranged such that optimal decision making necessitated choosing the smaller and more probabilistic choice to have the most pellets at the end of a 30-minute interval. The rats, like most people in similar gambling tasks, made the choices that optimized their reward (i.e., smaller, more probable). It wasn’t until they were administered drugs that stimulated neurochemical changes similar to the neurochemical differences observed in disordered gamblers that the rats behaved less optimally.