Memory consolidation processes can be highly selective. For example, negative emotional aspects of events tend to be consolidated more readily than other, more neutral, aspects. This chapter discusses evidence that the sleeping brain provides an ideal environment for memory consolidation, and that active, as opposed to passive, sleep-based consolidation processes are particularly important in explaining why emotional memories are retained so well. I also review evidence that elevated levels of stress hormones (cortisol, norepinephrine), particularly during the time of the initial experience, support downstream emotional memory consolidation. The chapter then proposes a working model that describes why arousal and stress at encoding may set the stage for sleep to etch emotional memories in the brain on a long-lasting basis and presents recent data to support this model. However, in addition to promoting the consolidation and stabilization of emotional memories, evidence suggests that sleep and stress also transform memories—in both adaptive and maladaptive ways. Memory for negative emotional experiences, while adaptive in general, can also contribute to the etiology and perpetuation of clinical conditions such as depression and anxiety. Thus, I argues that it is possible to have “too much of a good thing” and suggests ways that the transformative nature of stress and sleep might be used to restructure maladaptive memories in the clinic.
Emotional Memory Formation Under Lower Versus Higher Stress Conditions