Although the emotional and motivational characteristics of dreaming have figured prominently in folk and psychoanalytic conceptions of dream production, emotions have rarely been systematically studied, and motivation, never. Because emotions during sleep lack the somatic components of waking emotions, and they change as the sleeper awakens, their properties are difficult to assess. Recent evidence of limbic system activation during REM sleep suggests a basis in brain architecture for the interaction of motivational and cognitive properties in dreaming. Motivational and emotional content (...) in REM and NREM laboratory mentation reports from 25 participants were compared. Motivational and emotional content was significantly greater in REM than NREM sleep, even after controlling for the greater word count of REM reports. (shrink)

Several theories claim that dreaming is a random by-product of REM sleep physiology and that it does not serve any natural function. Phenomenal dream content, however, is not as disorganized as such views imply. The form and content of dreams is not random but organized and selective: during dreaming, the brain constructs a complex model of the world in which certain types of elements, when compared to waking life, are underrepresented whereas others are over represented. Furthermore, dream content is consistently (...) and powerfully modulated by certain types of waking experiences. On the basis of this evidence, I put forward the hypothesis that the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance. To evaluate this hypothesis, we need to consider the original evolutionary context of dreaming and the possible traces it has left in the dream content of the present human population. In the ancestral environment human life was short and full of threats. Any behavioral advantage in dealing with highly dangerous events would have increased the probability of reproductive success. A dream-production mechanism that tends to select threatening waking events and simulate them over and over again in various combinations would have been valuable for the development and maintenance of threat-avoidance skills. Empirical evidence from normative dream content, children's dreams, recurrent dreams, nightmares, post traumatic dreams, and the dreams of hunter-gatherers indicates that our dream-production mechanisms are in fact specialized in the simulation of threatening events, and thus provides support to the threat simulation hypothesis of the function of dreaming. Key Words: dream content; dream function; evolution of consciousness; evolutionary psychology; fear; implicit learning; nightmares; rehearsal; REM; sleep; threat perception. (shrink)

Since the discovery that the characteristics of dreaming sleep are far stronger in Stage 1 rapid eye movement sleep than in any other biological state, investigators have attempted to determine the relative responsibility of the tonic versus the phasic properties of REM sleep for the different characteristics of dreaming–features such as the amount of information in the dream report, the brightness and clarity of the visual images, shifts in thematic continuity, and incongruities of image and meaning. The present experiment is (...) designed to identify dream characteristics that are specifically associated with tonic changes in level of cortical activation within sleep. It samples reports of imagery and thought during spontaneous variations within one phase of the 24-h diurnal rhythm and across the REM-NREM sleep cycle in order to identify the independent and joint contributions of the two cycles to imagery and thought. The rising phase of the diurnal cycle in the late night and morning was estimated from clock time during the late night and early morning and was varied by delaying the sleep onset and waking time of the subjects. Considered together with other studies, the results suggest that the major determinant of vivid visual imagery and enhanced cognitive activity during sleep is a pattern of subcortical and cortical activation that is common to both the REM phase of the REM-NREM cycle and the activated phase of the 24-h diurnal wake-sleep cycle. (shrink)