Michael Schredl

Continuity between waking activities and dream activities

Empirical studies largely support the continuity hypothesis of dreaming. Despite of previous research efforts, the exact formulation of the continuity hypothesis remains vague. The present paper focuses on two aspects: (1) the differential incorporation rate of different waking-life activities and (2) the magnitude of which interindividual differences in waking-life activities are reflected in corresponding differences in dream content. Using a correlational design, a positive, non-zero correlation coefficient will support the continuity hypothesis. Although many researchers stress the importance of emotional involvement on the incorporation rate of waking-life experiences into dreams, formulated the hypothesis that highly focused cognitive processes such as reading, writing, etc. are rarely found in dreams due to the cholinergic activation of the brain during dreaming. The present findings based on dream diaries and the exact measurement of waking activities replicated two recent questionnaire studies. These findings indicate that it will be necessary to specify the continuity hypothesis more fully and include factors (e.g., type of waking-life experience, emotional involvement) which modulate the incorporation rate of waking-life experiences into dreams. Whether the cholinergic state of the brain during REM sleep or other alterations of brain physiology (e.g., down-regulation of the dorsolateral prefrontal cortex) are the underlying factors of the rare occurrence of highly focused cognitive processes in dreaming remains an open question. Although continuity between waking life and dreaming has been demonstrated, i.e., interindividual differences in the amount of time spent with specific waking-life activities are reflected in dream content, methodological issues (averaging over a two-week period, small number of dreams) have limited the capacity for detecting substantial relationships in all areas. Nevertheless, it might be concluded that the continuity hypothesis in its present general form is not valid and should be elaborated and tested in a more specific way.

Effects of state and trait factors on nightmare frequency

In a new approach, this study compared the effects of trait and state factors on nightmare frequency in a non-clinical sample. Although neuroticism and boundary thinness were related to nightmare frequency, regression analyses indicated that the trait measures did not add to the variance explained by the state measures. This finding supports the so-called continuity hypothesis of dreaming, i. e., nightmares reflect negative waking-life experiences. Second, the moderate relationship between nightmare frequency and poor sleep quality was partly explained by the day-time measures of neuroticism and stress, but it can be assumed that nightmares are an independent factor contributing to complaints of insomnia. Longitudinal studies measuring nightmare frequency and stress on a daily basis will shed light on the temporal relationship between daytime measures and the occurrence of nightmares. It will be also very interesting to study the relationship between stress and nightmare frequency in a sample who have undergone cognitive-behavioral treatment for nightmares.

Questionnaires and Diaries as Research Instruments in Dream Research: Methodological Issues

Dream questionnaires are widely used in dream research to measure dream recall frequency and various aspects of dream life. The present study has investigated the intercorrelation between questionnaire and diary measures. 285 participants completed a dream questionnaire and kept a dream diary over a two-week period. Results indicate that keeping a dream diary increased dream recall in low and medium dream recallers but decreased dream recall in high dream recallers. The correlation coefficients between questionnaire items measuring aspects of dream content and diary data were large, except for a more complex scale (realism/bizarreness). In the low recall group, however, considerably lower coefficients were found indicating that recall and sampling processes affect the response to global items measuring dream content. Using the example of testing gender differences, the findings of the present study clearly indicate that the measurement technique affects the results. Whereas sufficient internal consistency and retest reliability have been demonstrated for various dream questionnaires, future research should focus on the aspects of validity by comparing questionnaire data to dream content analysis of at least 20 dreams per person.

Dreaming in Posttraumatic Stress Disorder: A Critical Review of Phenomenology, Psychophysiology and Treatment

This review summarizes the available knowledge on the phenomenology of posttraumatic dreams. Posttraumatic nightmares are reported by up to 70% of individuals suffering from posttraumatic stress disorder (PTSD). An extensive review of polysomnographic studies suggests that neither this high incidence nor the occurrence of posttraumatic nightmares throughout the sleep cycle can be explained by altered REM sleep parameters. The assumption that a reduction of dream recall may serve as a coping mechanism in PTSD patients is questionable. About 50% of posttraumatic dreams comprise exact replications of the traumatic events. Therefore dreams in PTSD do not have stereotypical content. Data characterizing non-replicative posttraumatic dreams and indicating a change in dream content over time must be considered preliminary. Occurrence of posttraumatic dreams is associated with psychopathological developments. Imagery Rehearsal Therapy has repeatedly been proven to be a valuable tool in treating patients suffering from posttraumatic dream disturbance. A deeper knowledge of posttraumatic dreams is essential for any theory of PTSD as well as for a better understanding of the overall function of dreaming.

Factors of home dream recall: a structural equation model

Previous research has indicated that personality factors such as openness to experience, creativity, visual memory, attitude toward dreams, and sleep behavior is related to home dream recall frequency (DRF). However, a study investigating all areas simultaneously within one sample in order to determine the percentage of variance explained by all variables and to take intercorrelations between the influencing factors into account has not been performed till now. The present study with 444 participants fills this gap. Using several indicators for each of the variables mentioned above, a structural equation model was tested. Although the model fit was satisfying, the four factors which were significantly related to DRF: personality (openness to experience, thin boundaries, absorption), creativity, nocturnal awakenings, and attitude toward dreams, explained only 8.4% of the total variance. As this value is considerably lower than those of studies investigating a single influencing factor and using similar measurement instruments in similar samples, one might speculate about possible expectancy effects in these previous studies, an effect which has been demonstrated for DRF in the laboratory setting. In addition, the small percentage of explained variance of each single factors (<3%) may indicate that other, in this study unmeasured, variables such as sleep duration (state aspect), introspection, and cognitive functioning immediately upon awakening (sleep inertia) show substantial covariance with the interindividual differences in DRF. Future studies should focus on longitudinal aspects in order to differentiate between state versus trait factors (although methodologic issues, e.g. the effect of the measurement technique on DRF itself, have to be clarified) and investigate additional variables which might be associated with DRF (see above).

The relationship between REM sleep and memory consolidation in old age and effects of cholinergic medication

BACKGROUND Recent findings in young adults suggest that rapid eye movement (REM) sleep plays a role in procedural memory consolidation. The significance of REM sleep for memory consolidation in old age has not yet been investigated. METHODS Effects of REM sleep manipulation on declarative and procedural memory consolidation were investigated in 107 healthy older adults, ages 60-82 years. Rapid eye movement sleep deprivation was achieved by REM sleep awakenings and compared with non-REM sleep awakenings. Rapid eye movement sleep augmentation was realized physiologically by REM sleep rebound and pharmacologically by administering an acetylcholinesterase inhibitor in a double-blind, placebo-controlled design. Memory performance was tested by a paired associate list and a mirror tracing task at 9:30 pm and 7:30 am with sleep intervening between 11:00 pm and 7:00 am. RESULTS Although REM sleep deprivation led to a significant reduction in total and phasic REM sleep, memory consolidation remained unaffected. Both REM sleep augmentation groups showed a significant increase in phasic REM sleep, whereas only pharmacological cholinergic REM sleep manipulation exerted a significant positive effect on procedural memory consolidation. CONCLUSIONS Because only after cholinergic stimulation of phasic REM sleep procedural memory consolidation is improved, cholinergic activation seems to be a crucial component of REM sleep-related memory consolidation in old age.

Donepezil-induced REM sleep augmentation enhances memory performance in elderly, healthy persons

Previous research in younger individuals has shown that acetylcholinesterase inhibitors may enhance REM sleep. The present study indicates that in the elderly, donepezil, an acetylcholinesterase inhibitor, also exerts a marked effect on REM sleep parameters--percentage of REM sleep and REM density were increased whereas REM latency was reduced. In addition, we also found a correlation between memory performance and REM sleep. Based on these findings, we conclude that there is an interrelationship between cognitive performance and amount of REM sleep in elderly humans as has been previously shown in animals and young adults.

Gender differences in dream recall: a meta‐analysis

Many studies have reported gender differences in dream recall. Data from 175 independent studies have been included in the analyses. Overall, estimated effect sizes in five age groups of healthy persons differed significantly from zero. Variables like measurement method and publication year did not affect the gender difference but age groups showed different effect sizes. The smallest effect size was found for children (0.097), the largest for adolescents (0.364), whereas the three adult groups ranged from 0.242 to 0.270. The findings suggest that the age‐dependent gender differences in dream recall might be explained by gender‐specific ‘dream socialization’. Longitudinal studies in this area, however, are still lacking.

Dreaming and insomnia: dream recall and dream content of patients with insomnia.

The present study investigated dream recall frequency and dream content of patients with insomnia in comparison to healthy controls. Patients’ dream recall frequency was elevated, due mainly to their heightened frequency of nocturnal awakenings. Dream content seems to reflect waking life stressors found in these patients, i.e. dream emotions were more negative and dreams were characterized by themes of depression, ‘negatives’ in self‐description and health themes. Patients taking antidepressants showed lower dream recall frequency than patients without any medication; benzodiazepine intake, however, did not affect dream recall frequency. Both drug groups reported more positively toned dreams than drug‐free patients. It is suggested that future studies should use more dreams per subject in order to reduce error variance of the dream content measures and more detailed measures of waking life stress.

Gender differences in nightmare frequency: A meta-analysis

Many studies have reported gender differences in nightmare frequency. In order to study this difference systematically, data from 111 independent studies have been included in the meta-analysis reported here. Overall, estimated effect sizes regarding the gender difference in nightmare frequency differed significantly from zero in three age groups of healthy persons (adolescents, young adults, and middle-aged adults), whereas for children and older persons no substantial gender difference in nightmare frequency could be demonstrated. There are several candidate variables like dream recall frequency, depression, childhood trauma, and insomnia which might explain this gender difference because these variables are related to nightmare frequency and show stable gender differences themselves. Systematic research studying the effect of these variables on the gender difference in nightmare frequency, though, is still lacking. In the present study it was found that women tend to report nightmares more often than men but this gender difference was not found in children and older persons. Starting with adolescence, the gender difference narrowed with increasing age. In addition, studies with binary coded items showed a markedly smaller effect size for the gender difference in nightmare frequency compared to the studies using multiple categories in a rating scale. How nightmares were defined did not affect the gender difference. In the analyses of all studies and also in the analysis for the children alone the data source (children vs. parents) turned out to be the most influential variable on the gender difference (reporting, age). Other results are also presented. Investigating factors explaining the gender difference in nightmare frequency might be helpful in deepening the understanding regarding nightmare etiology and possibly gender differences in other mental disorders like depression or posttraumatic stress disorder.