Dream content and memory processing: Dream lag effects within a single night and across several nights: A pilot study

Dream content may reflect elements of memory processing occurring within a single night and across several days or weeks. One 19-year-old healthy female college student kept a daily diary, a sleep diary, and recorded her dreams for 2 months. A preset alarm clock allowed her to sample dreams from both early NREM-rich and late REM-rich sleep. Dreams were examined for memory elements that were similar to diary entries. There were 55 scorable dreams obtained during 25 nights. Matches between dream elements and daytime events occurred quite frequently depending on dream element. Dream characters, actions, themes, and settings more often matched daytime memories than dream objects, emotions, or events. Matches were also time dependent. Emotions appeared in dreams after the subject experienced them sooner than all other elements (1.5 days), while objects took the longest to appear in dreams (3.5 days). With respect to within night cognitive processing, 42% of scorable nights contained the same memory elements in the first and last dreams and 8% of scorable nights contained the same emotion within the same context between an early and late dream. Selected dream elements appear to reflect memory processing occurring throughout the night and over the course of several days.