Sleep Loss Produces False Memories

People sometimes claim with high confidence to remember events that in fact never happened, typically due to strong semantic associations with actually encoded events. Sleep is known to provide optimal neurobiological conditions for consolidation of memories for long-term storage, whereas sleep deprivation acutely impairs retrieval of stored memories. Here, focusing on the role of sleep-related memory processes, we tested whether false memories can be created (a) as enduring memory representations due to a consolidation-associated reorganization of new memory representations during post-learning sleep and/or (b) as an acute retrieval-related phenomenon induced by sleep deprivation at memory testing. According to the Deese, Roediger, McDermott (DRM) false memory paradigm, subjects learned lists of semantically associated words (e.g., “night”, “dark”, “coal”,…), lacking the strongest common associate or theme word (here: “black”). Subjects either slept or stayed awake immediately after learning, and they were either sleep deprived or not at recognition testing 9, 33, or 44 hours after learning. Sleep deprivation at retrieval, but not sleep following learning, critically enhanced false memories of theme words. This effect was abolished by caffeine administration prior to retrieval, indicating that adenosinergic mechanisms can contribute to the generation of false memories associated with sleep loss

Gender differences in dream content: related to biological sex or sex role orientation?

Despite the large number of studies addressing gender differences in dream recall and dream content, research regarding whether these differences might be affected by sex role orientation is rather scarce. The present online-survey included a large sample of most recent dreams. The results clearly indicate that sex role orientation (femininity/expressivity and masculinity/instrumentality) affect the same dream characteristics that show marked gender differences (e.g., sexual dream content, physical aggression). Whereas the effect of sex role orientation on dream content support the continuity hypothesis of dreaming, the effect of biological sex on dream content does not exclude that other variables (such as, for example, the amount of sexual fantasies during waking) have an effect on dream content in addition to sex role orientation. Thus, future studies have to elicit more waking-life variables in order to model the varying daytime experiences of men and women in order to investigate whether these daytime differences sufficiently explain gender differences in dreaming or whether biological factors are also of importance. </jats:p

Proportion of false memories in the recognition test.

<p>Under sleep deprivation at retrieval false memory rate was significantly enhanced in Experiment I (higher false memory rate in the sleep deprived “night wake” group compared to both non-deprived groups), while sleep after learning compared to wakefulness did not increase false memories (no difference between the “night sleep” and “day wake” group). Experiments II and III further strengthen these findings in showing that sleep deprivation at retrieval also enhanced false memory rate when “sleep vs. wakefulness after learning” was held constant and subjects only were or were not sleep deprived at retrieval (“2^nd night wake” vs. “2^nd night sleep” in Experiment II), and that sleep after learning neither enhanced false memories when retrieval was tested after a recovery night and controlling for circadian phase (“1^st night wake” vs. “1^st night sleep” in Experiment III). The administration of caffeine one hour before retrieval testing in Experiment IV abolished the sleep deprivation-induced enhancement in false memories. False memory rate refers to the mean proportion of the judgment “old” to 18 theme words that were not presented during learning (mean±SEM). * P<0.05, ** P<0.01.</p

Subjective ratings at learning and retrieval.

<p>Subjective ratings ranged from 1 = “not at all” to 5 = “very much”. ^* P≤0.05, ^** P<0.01, compared to respective control groups within each experiment.</p

Experimental design.

<p>Subjects either slept or stayed awake in the consolidation phase following learning, and either were or were not sleep deprived at retrieval. Black fields refer to sleep periods; blank fields represent times of wakefulness. Times of learning (L) and retrieval (R) are indicated for Experiments I to IV.</p