Integration of conditioned threat with pre-existing memories.

How does negative affect spread through existing memories? Whereas many studies have investigated generalization of learned threat responses across perceptual and semantic dimensions, little attention has been given to the possibility that Pavlovian threat responses may spread beyond what is directly learned to previously encoded memories that overlap in content. Here, we increased the demand on associative memory in a modified sensory preconditioning task to investigate this. First, participants encoded 40 unique episodes, each consisting of two neutral stimuli. On the following day, one of each pair was newly associated with either an aversive or a neutral stimulus. Another day later, both stimuli of the original memories were found to trigger enhanced pupil dilation if one was indirectly linked to an aversive stimulus. This effect was independent of whether the associations encoded on day 1 were accurately retained on the day of testing, and confined to trials on which the indirectly associated stimulus was consciously brought to mind, suggesting the formation of a link that directly connects preconditioned stimuli to subsequently learned aversive outcomes. The present study demonstrates that the human defensive system is remarkably adept at quickly anticipating threat based on information acquired over separate events, and gives a first glimpse into the associative structures that enable this ability.