Effects of methamphetamine on signalled probability in rats using concurrent chains

Pigeons show a suboptimal choice for probabilistic reinforcement in the presence of informative stimuli, which has been proposed as an animal model of gambling. However, this behaviour has been difficult to replicate in rats. In our study, rats responded on alternatives that provided 50% or 100% reinforcement with half of the sessions reliably signalled and half un-signalled. Contrary to expectation, rats preferred the optimal alternative to a greater extent in the signalled sessions compared to the un-signalled sessions. Acute methamphetamine increased preference for the 50% alternative exclusively in signalled sessions. These results suggest that rats, unlike pigeons, are able to use the information provided by the stimulus correlated with non-reinforcement to shift preference away from the suboptimal alternative, and that the influence of methamphetamine on rats' probabilistic choice is context dependent.