Two experiments examined the effects of varying the probability of “wins” within a rat model of gambling. On a concurrent-chains procedure, rats could choose between a “work” lever on which a fixed 20 responses produced a food pellet or a “gamble” lever, where on some trials (“wins”) only one response was required for reinforcement while on other trials 40 responses were required. Despite the fact that the work lever was always associated with the higher overall reinforcement rate, rats frequently chose to respond on the gamble lever. The frequency with which rats chose the gamble lever varied as a function of win probability. Extinction of the gamble choice (i.e., gamble-lever choices no longer resulted in wins) resulted in consistent choice of the work lever. The behavioral baselines reported in the present study may prove useful for investigators interested in employing a rat model of gambling.



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