Optimal behavior by rats in a choice task is associated to a persistent conditioned inhibition effect

• Rats preference for discriminative vs non-discriminative alternatives differing in probability of reinforcement was studied.
• We also analyzed the relationship between choice behavior and the effects of the conditioned inhibitor.
• We replicated the finding of optimal choice behavior, in contrast to pigeons’ suboptimal choice.
• Optimal choice behavior was associated to a strong effect of the conditioned inhibitors.
• The conditioned inhibition did not dissipate, in contrast to what has been found in pigeons.

When given a choice between an alternative with a low probability of reinforcement and discriminative stimuli, and another with a higher probability of reinforcement and non-discriminative stimuli, pigeons show a clear preference for the former but rats clearly prefer the later. It has been reported that pigeon’s suboptimal choice is associated to a diminishing effect of the stimulus correlated with non-reinforcement. In the present paper, we explored the possibility that rats' optimal choice is more strongly influenced than pigeons' by the stimulus associated to non-reinforcement and that the effects of it do not dissipate during training. We trained rats to choose between an alternative with 0.50 probability of reinforcement and discriminative stimuli, and an alternative with 0.75 probability of reinforcement and non-discriminative stimuli. We replicated the strong preference for the optimal alternative. Then, after several sessions of training, we presented summation trials in which both the stimulus associated to reinforcement and the stimulus associated to non-reinforcement were simultaneously presented. The results showed that the stimulus associated to non-reinforcement exerted a strong effect on choice, and, more importantly, that it did not seem to dissipate across training. These results suggest that the strong difference found between pigeons and rats in the suboptimal choice procedure is potentially related to differences in the impact of conditioned inhibitors.