Wake and be fine? : The effect of sleep on emotional memory

Abstract: The aim of this thesis was to examine the effect of sleep on emotional memories. The first two studies examined the role of sleep in the generalization of fear learning and the third study examined how sleep affected the forgetting of unwanted emotional memories.In study 1, participants first underwent fear conditioning with a small and a large circle as the CS+ and the CS-. Next, after either a nap or an equal amount of time spent awake, participants viewed these two circles again, as well as eight novel circles that gradually varied in size in-between the former two. The results showed that fear conditioning was successful and that that there was a tendency towards the larger responses to the CS+ as compared to the CS- having been preserved during the delay interval but that there was no group difference. Analyzing responses to the novel stimuli revealed that fear responses increased as a function of their similarity to the CS+. This increase did however not differ between the groups, thus there was no support for that sleep or wake would differently affect the generalization of fear learning.In study 2, a similar design was used, but with electric shocks instead of the aversive sound, in order to elicit a stronger fear response. The results revealed that in the wake group, fear responses were larger to the CS+ compared to the CS-, whereas no such effect was observed after sleep. Similar results were evident for fear responses to the novel circles, indicating that after sleep, similarity to the CS+ was no longer a predictor of the degree of fear responding. The groups did not differ in general responsivity, but only in how their responses were distributed across the stimuli.In study 3, participants first learned associations between neutral words and images that were either negative or neutral. Then, in the Think/No-Think phase, a subset of these words were shown without the images, and participants were asked to either try to think of the image that they had previously been associated with (Think items) or to avoid all thoughts of the associated image (No-Think items). Then, memory was tested for all the items. Results revealed significant below baseline forgetting of the No-Think items in the group that was tested right after the conclusion of the No-Think phase. This forgetting effect had however disappeared after a longer delay interval, regardless of if it had contained sleep or wake, regardless of the emotionality of the images. Thus, we found no support that sleep and wake would differently affect the duration of this forgetting effect.