No support for an effect of a daytime nap on the consolidation or generalization of fear learning

Abstract

This study examined the role of a daytime nap in the consolidation and generalization of fear learning. 31 healthy, young adult participants (16 in the wake group and 15 in the sleep group) underwent a fear acquisition procedure in which the conditioned stimulus (CS+), a composite image consisting of a geometrical figure imposed on a background, was repeatedly paired with a mild electric shock. The safety stimulus (CS-), another geometrical figure imposed on another background, was never paired with the shock. After a delay interval containing either a 2-h nap opportunity or an equivalent amount of time spent awake, participants performed a fear memory and generalization test. Here, participants viewed four different stimuli: the CS+ and CS- seen before, as well as two novel stimuli composed of the same two geometrical figures seen before imposed on novel background images. This design allowed us to examine a) whether sleep consolidates the original fear memory and b) whether sleep affects the degree of generalization of fear learning to the original fear-eliciting geometrical figure presented on a novel background image. Results revealed no group differences for either the consolidation or generalization of fear learning in any of our outcome measures (skin conductance responses, subjective ratings of unpleasantness, retrospective shock expectancy ratings, or explicit memory performance). This study adds to the body of work showing mixed findings on the effect of sleep on consolidation and generalization of fear learning, in which there is currently limited evidence for sleep having an effect in either direction.