Effects of optimism on gambling in the rat slot machine task

• We identified rats displaying ‘pessimistic’ and ‘optimistic’ traits.
• We determined how these traits affect behavior in the rat Slot Machine Task.
• ‘Optimistic’ rats were more likely to gamble in the hopeless ‘clear loss’ situation.
• We demonstrated interrelation between optimism and gambling in an animal model.

Although gambling disorder is a serious social problem in modern societies, information about the behavioral traits that could determine vulnerability to this psychopathology is still scarce. In this study, we used a recently developed ambiguous-cue interpretation ​(ACI)​ paradigm to investigate whether ‘optimism’ and ‘pessimism’ as behavioral traits may determine the gambling-like behavior of rodents. In a series of ACI tests (cognitive bias screening), we identified rats that displayed ‘pessimistic’ and ‘optimistic’ traits. Subsequently, using the rat slot machine task (rSMT), we investigated if the ‘optimistic’/‘pessimistic’ traits could determine the crucial feature of gambling-like behavior that has been investigated in rats and humans: the ​interpretation of ‘near-miss’ outcomes as a positive (i.e., win) situation. We found that ‘optimists’ did not interpret ‘near-miss’, ‘near loss’, or ‘clear win’ as win trials more often than ​their ‘pessimistic’ ​conspecifics; however, the ‘optimists’ were statistically more likely to reach for a reward in the hopeless ‘clear loss’ situation. This agrees with human studies and provides a platform for modeling interactions between behavioral traits and gambling in animals.