Visual and emotional aspects of waking memories follow different paths as people fall asleep. Healthy adults viewed an emotional image, then were awakened seconds to minutes later during wakefulness, N1, or N2 sleep stages. Semantic similarity between the image and subsequent hypnagogic imagery—the 'image residue'—persisted and even increased during N1 sleep, lasting longer with more time in that stage. In contrast, the emotional tone of the image—the 'affect residue'—gradually faded as sleep progressed, becoming neutralized and reaching its lowest point during N2. Brain theta power (4.5–6.5 Hz) during N1 was inversely related to image residue. These findings suggest that visual content and strong negative emotions may decouple at sleep onset, possibly aiding emotional processing.
Slow wave activity during a nap and dreams related to a stressful video game predict better post-sleep performance for people in a low-agency, prey-like role, but not for those in a high-agency predator role. Thirty adult pairs played a first-person shooter game against each other, then napped while EEG and ECG were recorded, reported dreams, and played again. For participants assigned the prey role, score improvements correlated positively with slow wave activity during the nap, how much dreams related to the game, and heart rate variability during the first round. No such correlations appeared for predator-role participants, suggesting sleep's adaptive function may be especially important for individuals facing threatening, low-control situations.