Second-order conditioning of safety in male and female rats.

Stimuli can acquire meaning and significance indirectly by being paired with other stimuli that already have known outcomes. When a stimulus has a well-established association with either aversive or rewarding consequences, other neutral stimuli can take on similar properties simply by occurring alongside it - even if the original outcome is not presented. This process is known as second-order conditioning. Relatively few studies have examined second-order conditioning of inhibitory safety memories. Here, we examined second-order conditioning of safety in adult male and female Long-Evans rats by adapting our well-established first-order safety conditioning paradigm to include novel stimuli paired with the established safety cue. Our findings demonstrate that a second-order safety cue can attenuate fear responses to a degree comparable to that of a first-order safety cue. In contrast, a novel cue that had never been paired with a safety signal failed to produce an equivalent reduction in defensive behavior during fear cue presentation, demonstrating that the reduced fear to the second-order safety cue was a product of conditioning and not external inhibition. Developing methods to generalize safety to novel stimuli that have not been explicitly conditioned for safety holds significant promise for advancing innovative strategies aimed at mitigating maladaptive fear responses.