Waking Events Research Articles

The Ecology of Human Sleep (EcoSleep) Cohort Study: Protocol for a longitudinal repeated measurement burst design study to assess the relationship between sleep determinants and outcomes under real-world conditions across time of year.

The interplay of daily life factors, including mood, physical activity, or light exposure, influences sleep architecture and quality. Laboratory-based studies often isolate these determinants to establish causality, thereby sacrificing ecological validity. Furthermore, little is known about time-of-year changes in sleep and circadian-related variables at high resolution, including the magnitude of individual change across time of year under real-world conditions. The Ecology of Human Sleep (EcoSleep) cohort study will investigate the combined impact of sleep determinants on individuals' daily sleep episodes to elucidate which waking events modify sleep patterns. A second goal is to describe high-resolution individual sleep and circadian-related changes across the year to understand intra- and inter-individual variability. This study is a prospective cohort study with a measurement-burst design. Healthy adults aged 18-35 years (N = 12) will be enrolled for 12 months. Participants will continuously wear actimeters and pendant-attached light loggers. A subgroup will also measure interstitial fluid glucose levels (six paticipants). Every 4 weeks, all participants will undergo three consecutive measurement days of four ecological momentary assessments each day ('bursts') to sample sleep determinants during wake. Participants will also continuously wear temperature loggers (iButtons) during the bursts. Body weight will be captured before and after the bursts in the laboratory. The bursts will be separated by two at-home electroencephalogram recordings each night. Circadian phase and amplitude will be estimated during the bursts from hair follicles, and habitual melatonin onset will be derived through saliva sampling. Environmental parameters (bedroom temperature, humidity, and air pressure) will be recorded continuously.

Obesity‐Induced Breathing Variability During Sleep Is Independent of Apneas and Sleep Fragmentation

IntroductionObesity is a major cause of sleep‐disordered breathing (SDB). Conventional metrics of SDB, such as the apnea‐hypopnea index, can be confounded by the effects of obesity on oxygenation and lack of standard definitions. Thus, the impact of SBD on sleep is often difficult to quantify. Sleep fragmentation is frequently observed in obese individuals, but whether it occurs independently of SDB remains unknown. Quantitative analysis of ventilation may delineate the effects of obesity on breathing patterns and sleep fragmentation. We aimed to examine the effects of obesity on respiratory patterns during sleep and the relationship between obesity‐related respiratory variability and sleep fragmentation.MethodsSleep recordings were performed in 15 male lean C57BL/6J mice and 17 male diet‐induced obese (DIO) mice on the same genetic background. We applied Poincaré analysis of minute ventilation (VE) during sleep to estimate the breathing variability. Apneas were scored as ≥90% reductions in airflow for two breath cycles or ≥0.7s regardless the presence of arousals. Arousals were defined as single waking events lasting less than 16s. Arousals were classified as respiratory when associated with ≥30% drops in VEfrom baseline.ResultsBreathing variability was significantly higher in DIO mice during NREM sleep, but not during REM sleep. Obesity was associated with an increased apnea severity and 45% greater sleep fragmentation. However, obesity‐induced breathing variability was not affected by apnea or arousal indexes. Respiratory arousals comprised 15% of the arousals in both strains.ConclusionsObesity increased respiratory variability during NREM sleep independently of apneas and macro‐sleep architecture. Obesity caused sleep fragmentation that was not fully explained by SDB severity. Our quantitative analysis of VE identified differences in breathing variability in obesity that were not captured by traditional SDB metrics, which may be applicable for human SDB.

Evaluating the Relationship Between Fitbit Sleep Data and Self-Reported Mood, Sleep, and Environmental Contextual Factors in Healthy Adults: Pilot Observational Cohort Study.

BackgroundMental health disorders can disrupt a person’s sleep, resulting in lower quality of life. Early identification and referral to mental health services are critical for active duty service members returning from forward-deployed missions. Although technologies like wearable computing devices have the potential to help address this problem, research on the role of technologies like Fitbit in mental health services is in its infancy.ObjectiveIf Fitbit proves to be an appropriate clinical tool in a military setting, it could provide potential cost savings, improve clinician access to patient data, and create real-time treatment options for the greater active duty service member population. The purpose of this study was to determine if the Fitbit device can be used to identify indicators of mental health disorders by measuring the relationship between Fitbit sleep data, self-reported mood, and environmental contextual factors that may disrupt sleep.MethodsThis observational cohort study was conducted at the Madigan Army Medical Center. The study included 17 healthy adults who wore a Fitbit Flex for 2 weeks and completed a daily self-reported mood and sleep log. Daily Fitbit data were obtained for each participant. Contextual factors were collected with interim and postintervention surveys. This study had 3 specific aims: (1) Determine the correlation between daily Fitbit sleep data and daily self-reported sleep, (2) Determine the correlation between number of waking events and self-reported mood, and (3) Explore the qualitative relationships between Fitbit waking events and self-reported contextual factors for sleep.ResultsThere was no significant difference in the scores for the pre-intevention Pittsburg Sleep Quality Index (PSQI; mean 5.88 points, SD 3.71 points) and postintervention PSQI (mean 5.33 points, SD 2.83 points). The Wilcoxon signed-ranks test showed that the difference between the pre-intervention PSQI and postintervention PSQI survey data was not statistically significant (Z=0.751, P=.05). The Spearman correlation between Fitbit sleep time and self-reported sleep time was moderate (r=0.643, P=.005). The Spearman correlation between number of waking events and self-reported mood was weak (r=0.354, P=.163). Top contextual factors disrupting sleep were “pain,” “noises,” and “worries.” A subanalysis of participants reporting “worries” found evidence of potential stress resilience and outliers in waking events.ConclusionsFindings contribute valuable evidence on the strength of the Fitbit Flex device as a proxy that is consistent with self-reported sleep data. Mood data alone do not predict number of waking events. Mood and Fitbit data combined with further screening tools may be able to identify markers of underlying mental health disease.

Integration of waking experience through dreams considered in light of individual differences in implicit learning ability.

The present study explored whether individual differences in implicit learning were related to the incorporation of waking events into dreams. Participants (N=60) took part in a sequence learning task, a measure of implicit learning ability. They were then asked to keep a record of their waking experiences (personally significant events [PSEs]/major concerns), as well as their nightly dreams for a week. Of these, the responses of 51 participants were suitable for further analysis in which participants themselves and three independent judges rated the correlation between waking events and dreams of the same day. Implicit learning ability was found to significantly correlate with the incorporation of PSEs into dreams. The present results may lend support to the Horton and Malinowski autobiographical memory (AM) model, which accounts for the activation of memories in dreams as a reflection of sleep-dependent memory consolidation processes that focusses in particular on the hyperassociative nature of AM during sleep.

Relationship Between Personality Types in MBTI and Dream Structure Variables.

This study aimed to explore relationships between personality type variables and dream structure variables. In the questionnaire experiment (N = 410), we investigated associations between different personality variables in the Myers-Briggs Type Indicator questionnaire (MBTI) and various aspects of dreams in the Mannheim Dream questionnaire (MADRE). The MBTI has four dimensions. In the Extroversion/Introversion (E/I) dimension, I types dreamt more of emotional intensity and passive emotions than E types. In addition, I types may become more distressed in nightmares than E types. E types more frequently shared their dreams with others. In the Sensation/Intuition (S/N) dimension, N types had a more positive attitude toward dreams and can get more novel ideas and help from their dreams than S types. In the dream diary experiment (N = 47), we investigated whether the S/N dimension may influence waking events’ incorporation into dreams. External judges decoded paired waking events and dream reports. N types had more metaphorical incorporation than S types. More specifically, N types had more metaphorical expressions in their dreams than S types. This result may be due to the different characteristics between S types and N types. It may provide support for the dream continuity hypothesis.

A Paradigm for Matching Waking Events Into Dream Reports.

In this study, participants recorded their waking events (Personal significant events, PSEs/Major concerns, MCs) and dream reports for 7 days. These events and dreams were paired by the same day (216 PSEs-dreams pairs and 215 MCs-dreams pairs). Then participants were instructed to both find similar features (characters, objects, locations, actions, emotions, and themes) of their events-dreams pairs and give a match score of their events-dreams pairs. Besides, we proposed a method for independent judges to match waking events into dreams (the external ratings). The rating standard of the external-ratings was to look for similar behaviors between events and dreams. Based on this rating standard, three independent judges were instructed to rate participants’ events- dreams pairs. Firstly, we compared the two kinds of methods of self-ratings. Spearman correlations showed that the two methods were significantly correlated with each other. These results suggested that the sum of different kinds of similar features could be used to represent self-ratings reported of the degree of the correlation between a waking event and a dream. Regression correlations showed that for PSEs-dreams pairs, actions, emotions, and themes were similar features that affected the degree of the correlation between an event and a dream of the same day, and for MCs-dreams pairs, emotions, and themes were similar features that affected the degree of the correlation between an event and a dream of the same day. These results suggested that different kinds of similar features had different influence on the self-ratings’ evaluation for the degree of matching between waking event and dream. Secondly, we compared the rating results of the self-ratings and the rating results of the external-ratings. Spearman correlations showed that the results of the self-ratings were significantly correlated with the results of the external-ratings. So this study’s method for the external ratings may be suitable for future studies. Besides, as the external ratings of this study can rate dream metaphors, we also made a short discussion on dream metaphors. Future studies can use the method to explore dream metaphors.

No cognitive processing in the unconscious, anesthetic-like, state of sleep.

We review evidence challenging the hypothesis that memories are processed or consolidated in sleep. We argue that the brain is in an unconscious state in sleep, akin to general anesthesia (GA), and hence is incapable of meaningful cognitive processing-the sole purview of waking consciousness. At minimum, the encoding of memories in sleep would require that waking events are faithfully transferred to and reproduced in sleep. Remarkably, however, this has never been demonstrated, as waking experiences are never truly replicated in sleep but rather appear in very altered or distorted forms. General anesthetics (GAs) exert their effects through endogenous sleep-wake control systems and accordingly GA and sleep share several common features: sensory blockade, immobility, amnesia and lack of awareness (unconsciousness). The loss of consciousness in non-REM (NREM) sleep or to GAs is characterized by: (a) delta oscillations throughout the cortex; (b) marked reductions in neural activity (from waking) over widespread regions of the cortex, most pronounced in frontal and parietal cortices; and (c) a significant disruption of the functional connectivity of thalamocortical and corticocortical networks, particularly those involved in "higher order" cognitive functions. Several (experimental) reports in animals and humans have shown that disrupting the activity of the cortex, particularly the orbitofrontal cortex, severely impairs higher order cognitive and executive functions. The profound and widespread deactivation of the cortex in the unconscious states of NREM sleep or GA would be expected to produce an equivalent, or undoubtedly a much greater, disruptive effect on mnemonic and cognitive functions. In conclusion, we contend that the unconscious, severely altered state of the brain in NREM sleep would negate any possibility of cognitive processing in NREM sleep.

A Survey of Koreans on Sleep Habits and Sleeping Symptoms Relating to Pillow Comfort and Support.

The number of people who complain of sleep disturbances is steadily increasing. An understanding of sleep-related factors is required to address sleep problems. This survey study investigated the sleep habits and sleeping symptoms relating to the comfort and support characteristics of pillows and the relationship between sleep quality and pillow design factors. The study utilized data from 332 participating Korean adults aged 20–76 years (mean age ± SD: males, 40.4 ± 15.2; females, 42.9 ± 15.4). We developed a questionnaire that evaluated sleep habits (sleep duration, bedtime, wake-up time and sleeping position); sleeping symptoms (snoring or coughing, breathing and sleepiness during waking hours) based on the Korean version of the Pittsburgh Sleep Quality Index (PSQI-K) questionnaire; and pillow-related factors (support, comfort, fatigue, height and shape) from existing pillow studies. The average sleep duration was 6.8 h, with more than half (52%) of participants sleeping in the supine position. The overall score for sleep quality was considered poor (4.84 points on a seven-point Likert scale), with some degree of sleepiness during waking hours (4.4 points on a seven-point Likert scale). Females went to bed earlier than males and were more likely to sleep in the lateral position compared to males. The number of toss and turn or waking events during sleep increased with age, and older individuals went to sleep earlier and woke up earlier. Among the symptoms of fatigue, pain, discomfort with changing position, snoring, coughing and breathing discomfort, participants reported their highest levels of discomfort due to sleepiness after waking, and they experienced the least head pain. Participants who used a regular-type pillow had poorer satisfaction on multiple comfort and support factors (support, comfort, height suitability, shape suitability) compared with those who used a functional-type pillow. Less head fatigue, less neck fatigue and less shoulder pain had significant effects on sleep quality. To reduce neck fatigue and shoulder pain, designers should consider the height for neck support in the lateral position. To reduce neck fatigue, it is desirable to use materials like latex or memory foam that provide neck support, which can improve sleep quality. The findings of this study contribute to a better understanding of sleep habits and characteristics of pillow comfort and provide practical guidelines for better pillow designs.

Posterior Hippocampal Spindle Ripples Co-occur with Neocortical Theta Bursts and Downstates-Upstates, and Phase-Lock with Parietal Spindles during NREM Sleep in Humans.

Human anterior and posterior hippocampus (aHC, pHC) differ in connectivity and behavioral correlates. Here we report physiological differences in humans of both sexes. During NREM sleep, the human hippocampus generates sharpwave ripples (SWRs) similar to those which in rodents mark memory replay. We show that while pHC generates SWRs, it also generates approximately as many spindle ripples (SSR: ripples phase-locked to local spindles). In contrast, SSRs are rare in aHC. Like SWRs, SSRs often co-occur with neocortical theta bursts (TBs), downstates (DSs), sleep spindles (SSs), and upstates (USs), which coordinate cortico-hippocampal interactions and facilitate consolidation in rodents. SWRs co-occur with these waves in widespread cortical areas, especially frontocentral. These waves typically occur in the sequence TB-DS-SS-US, with SWRs usually occurring before SS-US. In contrast, SSRs occur ∼350 ms later, with a strong preference for co-occurrence with posterior-parietal SSs. pHC-SSs were strongly phase-locked with parietal-SSs, and pHC-SSRs were phase-coupled with pHC-SSs and parietal-SSs. Human SWRs (and associated replay events, if any) are separated by ∼5 s on average, whereas ripples on successive SSR peaks are separated by only ∼80 ms. These distinctive physiological properties of pHC-SSR enable an alternative mechanism for hippocampal engagement with neocortex.SIGNIFICANCE STATEMENT Rodent hippocampal neurons replay waking events during sharpwave ripples (SWRs) in NREM sleep, facilitating memory transfer to a permanent cortical store. We show that human anterior hippocampus also produces SWRs, but spindle ripples predominate in posterior. Whereas SWRs typically occur as cortex emerges from inactivity, spindle ripples typically occur at peak cortical activity. Furthermore, posterior hippocampal spindle ripples are tightly coupled to posterior parietal locations activated by conscious recollection. Finally, multiple spindle ripples can recur within a second, whereas SWRs are separated by ∼5 s. The human posterior hippocampus is considered homologous to rodent dorsal hippocampus, which is thought to be specialized for consolidation of specific memory details. We speculate that these distinct physiological characteristics of posterior hippocampal spindle ripples may support a related function in humans.

An Attempt at Matching Waking Events Into Dream Reports by Independent Judges.

Correlations between memories and dreaming has typically been studied by linking conscious experiences and dream reports, which has illustrated that dreaming reflects waking life events, thoughts, and emotions. As some research suggests that sleep has a function of memory consolidation, and dreams reflect this, researching this relationship further may uncover more useful insights. However, most related research has been conducted using the self-report method which asks participants to judge the relationship between their own conscious experiences and dreams. This method may cause errors when the research purpose is to make comparisons between different groups, because individual differences cannot be balanced out when the results are compared among groups. Based on a knowledge of metaphors and symbols, we developed two operationalized definitions for independent judges to match conscious experiences and dreams, the descriptive incorporation and the metaphorical incorporation, and tested their reliability for the matching purpose. Two independent judges were asked to complete a linking task for 212 paired event-dreams. Results showed almost half dreams can be matched by independent judges, and the independent-judge method could provide similar proportions for the linking task, when compared with the self-report method.

Dream-reality confusion in borderline personality disorder: a theoretical analysis.

This paper presents an analysis of dream-reality confusion (DRC) in relation to the characteristics of borderline personality disorder (BPD), based on research findings and theoretical considerations. It is hypothesized that people with BPD are more likely to experience DRC compared to people in non-clinical population. Several variables related to this hypothesis were identified through a theoretical analysis of the scientific literature. Sleep disturbances: problems with sleep are found in 15–95.5% of people with BPD (Hafizi, 2013), and unstable sleep and wake cycles, which occur in BPD (Fleischer et al., 2012), are linked to DRC. Dissociation: nearly two-thirds of people with BPD experience dissociative symptoms (Korzekwa and Pain, 2009) and dissociative symptoms are correlated with a fantasy proneness; both dissociative symptoms and fantasy proneness are related to DRC (Giesbrecht and Merckelbach, 2006). Negative dream content: People with BPD have nightmares more often than other people (Semiz et al., 2008); dreams that are more likely to be confused with reality tend to be more realistic and unpleasant, and are reflected in waking behavior (Rassin et al., 2001). Cognitive disturbances: Many BPD patients experience various cognitive disturbances, including problems with reality testing (Fiqueierdo, 2006; Mosquera et al., 2011), which can foster DRC. Thin boundaries: People with thin boundaries are more prone to DRC than people with thick boundaries, and people with BPD tend to have thin boundaries (Hartmann, 2011). The theoretical analysis on the basis of these findings suggests that people who suffer from BPD may be more susceptible to confusing dream content with actual waking events.

Rehearsal of dreams and waking events similarly improves the quality but not the quantity of autobiographical recall.

Rehearsal of dreams and waking events similarly improves the quality but not the quantity of autobiographical recall.

Recall and recognition of dreams and waking events: A diary paradigm

Summary: Dream recall is often considered to be poor, although it is rarely systematically compared to the retrieval of waking event memories. A diary paradigm was implemented to explore the memory profile of recalled dreams over time, in comparison to recalled waking experiences. Twenty-five participants completed a dream and waking-event diary over two weeks. Titles of reports were re-presented in a surprise recall task. Subsequently, extracts of the reports were represented for recognition. No significant differences were found between dream and waking event memories in terms of either recall or recognition although some differences were found in terms of recollective experience, with waking-events being rememberedas episodic memories more than dreams. Diary dream memories that are recalled, reported and to some extent rehearsed are therefore accessible and detailed in a similar manner to waking experiences, providing that they are adequately encoded close to their time of occurrence. The continuity of retrieval processes over sleep and wake is outlined.

How Evaluating Dreams Makes History: Asabano Examples

Among the Asabano of Papua New Guinea, dreams deemed true have motivated hunting expeditions, medical treatments, and religious conversion. In contrast, dreams deemed false have negligibly affected behaviour. The Asabano draw on multiple and changing opinions and theories of dreams and dreaming when assessing whether or not particular dreams accurately represented reality. Dreams conforming to several dream scenario genres routinely receive attention as potential “true” dreams. These scenarios concern hunting, illness, death, and since contact, Christianity. Analysis of subsequent waking events resolves ambiguous cases. Asabano dream theories have changed in response to enculturation, diffusion, and personal experiences. Theories and methods of evaluating remembered dreams influence agency and events. I argue that classifying particular dreams as true or false is an historical process because once a remembered dream is labelled “true” or “false” it motivates appropriately responsive action or inaction.

Relief Expectation and Sleep

Originally, a role for sleep in learning and memory has been advocated following the observation of sleep-dependent performance enhancements at simple procedural tasks. With the investigation of a variety of cognitive and behavioral abilities, multiple stages of memory were further suggested to benefit from the off-line reprocessing believed to occur during specific sleep stages. In particular, REM sleep has been implicated in the integration of new information into associative networks as well as in the abstraction and generalization of implicit rules allowing adaptive behaviors. In a recent study, we extended these observations by demonstrating that the mediating effect of expectation on placebo-induced analgesia is strengthened by sleep, and that the individual amount of REM sleep is predictive of the relief expected on the next morning. However, this relation is strongly modulated by the level of concordance between expectations and sensory information available prior to sleep. As placebo responses derive from the learned association between contextual cues and subsequent relief, these results are discussed in relation to the proposed roles of REM sleep in the integrative stages of memory processing. In light of the responsiveness of REM sleep to waking events, its expression is also proposed to reflect the cognitive demand associated with the offline reprocessing of information necessary for the assimilation of new expectations to one's belief system.

Sleep and rest facilitate implicit memory in a visual search task

Several forms of learning have been demonstrated to show improvements with sleep. Based on rodent models, it has been suggested that replay of waking events in the hippocampus during sleep may underlie memory consolidation in humans. However, behavioral data for the role of sleep in human hippocampal-related memory have been inconsistent. To further investigate the role of sleep in hippocampal-mediated learning, we tested subjects in two sessions of a contextual cueing paradigm, a form of hippocampus-dependent implicit learning, separated by intervals of sleep, active wake, or carefully controlled quiet rest. Participants completed a visual search task, and unbeknownst to them, some search displays were occasionally repeated in the experiment. Contextual cueing was revealed by faster search speed on repeated trials ( Old) than unrepeated ones ( New), even though subjects were unaware of the trial repetition. Notably, performance in a second testing session was equivalent for participants who underwent quiet resting, daytime sleep, or nocturnal sleep between the two sessions. These four groups showed equivalent transfer of learning from Session 1. Notably, learning of New configurations in Session 2 was absent in the active wake group, but was equally strong among the other three groups. These results indicate that this form of hippocampal learning is independent of sleep, and vulnerable to proactive interference during active wake. They prompt a reevaluation of the hippocampal replay hypothesis as a general model of sleep-dependent learning.

The role of intrinsic and extrinsic factors in infant night waking.

Parents of young infants are faced with a number of adjustments and challenges. In particular, during the first few weeks or months following birth, infants require feeding at regular intervals throughout the day and night. Infants signal their need to be fed by crying, and thus the nighttime of parents is frequently disrupted by the cry signal and the need to awaken to feed the infant, change the infant's diaper, and soothe the infant back to sleep. Most parents know to expect these interruptions to their during early infancy, and many mothers and some fathers are able to devote full time to the many demands of caring for a young infant by foregoing employment or taking maternity or paternity leave from their jobs. By 3-4 months, however, most infants no longer physiologically require feedings, and most infants have adapted to a daily rhythm in which they more at than during the day. Although essentially all infants continue to awaken at at 3 months, about half of them are able to return to without signaling and without parental intervention (Karraker & Cottrell, 2000). The other half signal to their parents when they awaken, and often require feeding, rocking, and other parental assistance to return to sleep. These signaled awakenings continue throughout the first year and beyond for a significant proportion of infants, and some infants who begin to sleep through the (meaning that they do not signal to their parents following an awakening) at some point in early infancy return to a pattern of signaled waking around 9 months. These signaled waking behaviors (henceforth referred to simply as night waking) beyond the first few months of infancy are the focus of the present discussion. They are of concern to parents and practitioners primarily because of their impact on parents. Parents whose is frequently shortened and fragmented experience substantial deprivation, which can cause daytime fatigue, irritability, motor and cognitive deficits, impaired decision making, and lack of motivation (Dement, 1999; Pilcher & Huffcutt, 1996). It has been estimated that parents of infants lose an average of 2 hours of per from birth to 5 months, and 1 hour of per from 6 to 24 months (Dement, 1999). Sadeh and Anders (1993) also report that infant difficulties are the most common concern parents report to pediatricians at well-baby visits. The present paper addresses what is known about infants' waking, with a focus on the role of environmental causes and correlates of individual differences in this behavior. To provide context, the discussion begins with a review of the normative developmental course of infant waking, followed by a description of the effects of deprivation on adults. Then, factors associated with individual differences in the frequency of waking are described. Both intrinsic factors (characteristics of infants) and extrinsic factors (parent behaviors, family environment, etc.) are addressed. Then, the types of interventions commonly used to reduce infant waking are summarized. Finally, a behavioral and developmental model of the causes and effects of infant waking is described and illustrated. Normative Developmental Changes in Night Waking During Infancy Information about infant behavior is based primarily on maternal reports, video recordings, and actigraph recordings. An actigraph is a wristwatch-like device that is typically attached to the infant's leg and that records movements for later analysis. Hayes (2002) discussed the relative value of these different methods. Although video and actigraph recordings are more objective and detailed than maternal reports, they can be costly, intrusive, and difficult to use. Further, the sole use of actigraph recordings makes it difficult to discriminate signaled and unsignaled waking events. …

The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming.

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.

Paradoxical sleep as a programming system.

The concept of 'psychological individuation' i.e 'intraspecific variability' is essential for evolution as stated by Mayr (1958). It has been recently revived by the study of Bouchard (1990) in homozygous twins separated at birth and reared in different environments. These twins still retain identical psychological idiosyncratic reactions. Even if their brains are almost identical at birth, it is most likely that the different epigenetic stimuli from the external world have differently altered many cerebral synaptic circuitry due to the plasticity of the brain. Therefore, in order to maintain an identical psychological profile, there should be a mechanism which would reinforce the genetic programmation of the central nervous system either in reinforcing or erasing special genetic circuitry which would be stimulated during previous and/or subsequent waking periods. In ectothermic vertebrates, in immature mammals or sometimes in mature birds, this programming can be effectuated by neurogenesis. After neurogenesis has stopped in mammals, paradoxical sleep would be well suited for reinforcing the genetic programming during sleep. The patterns of portogeniculo-occipital (PGO) activity (which depend upon genetic factors) would be responsible for this function, together with the theta activity of the hippocampus (read out of previous waking events) and fast cortical EEG. This programming would activate all the brain including the pyramidal motor system while movements would be suppressed by the system controlling muscle atonia.

Dream Reports and Autobiographical Memory

Two experiments investigated autobiographical memory by studying dream reports. The continuity of autobiographical memory in the waking state and in sleep was demonstrated via Crovitz and Schiffman's retention function. The retention function was found to hold for vivid memories of dreams and vivid memories of waking experiences. It was also found to hold for waking events referenced in dream reports. In addition, the incidence of day residues was examined. About half of the dream reports collected included references to waking events of the previous day. The results were discussed in light of Freud's theory of dreams and cognitive theories of memory.