Tore Nielsen

A review of mentation in REM and NREM sleep: "Covert" REM sleep as a possible reconciliation of two opposing models.

Numerous studies have replicated the finding of mentation in both rapid eye movement (REM) and nonrapid eye movement (NREM) sleep. However, two different theoretical models have been proposed to account for this finding: (1) a one-generator model, in which mentation is generated by a single set of processes regardless of physiological differences between REM and NREM sleep; and (2) a two-generator model, in which qualitatively different generators produce cognitive activity in the two states. First, research is reviewed demonstrating conclusively that mentation can occur in NREM sleep; global estimates show an average mentation recall rate of about 50% from NREM sleep – a value that has increased substantially over the years. Second, nine different types of research on REM and NREM cognitive activity are examined for evidence supporting or refuting the two models. The evidence largely, but not completely, favors the two-generator model. Finally, in a preliminary attempt to reconcile the two models, an alternative model is proposed that assumes the existence of covert REM sleep processes during NREM sleep. Such covert activity may be responsible for much of the dreamlike cognitive activity occurring in NREM sleep.

Disturbed dreaming, posttraumatic stress disorder, and affect distress: A review and neurocognitive model.

Nightmares are common, occurring weekly in 4%-10% of the population, and are associated with female gender, younger age, increased stress, psychopathology, and dispositional traits. Nightmare pathogenesis remains unexplained, as do differences between nontraumatic and posttraumatic nightmares (for those with or without posttraumatic stress disorder) and relations with waking functioning. No models adequately explain nightmares nor have they been reconciled with recent developments in cognitive neuroscience, fear acquisition, and emotional memory. The authors review the recent literature and propose a conceptual framework for understanding a spectrum of dysphoric dreaming. Central to this is the notion that variations in nightmare prevalence, frequency, severity, and psychopathological comorbidity reflect the influence of both affect load, a consequence of daily variations in emotional pressure, and affect distress, a disposition to experience events with distressing, highly reactive emotions. In a cross-state, multilevel model of dream function and nightmare production, the authors integrate findings on emotional memory structures and the brain correlates of emotion.

Quality of sleep and its daily relationship to pain intensity in hospitalized adult burn patients.

&NA; Sleep disturbances are frequently reported in victims following burn injuries. This prospective study was designed to assess sleep quality and to examine its daily relationship to pain intensity within the first week of hospitalization. Twenty‐eight non‐ventilated patients were interviewed during 5 consecutive mornings (number of observations=140) to collect information about perceived quality of sleep (visual analogue scale, number of hours, number of awakenings, presence of nightmares). Pain intensity was assessed at rest (nighttime, morning, during the day) and following therapeutic procedures using a 0–10 numeric scale. Seventy‐five percent of patients reported sleep disturbances at some point during the study although, in most patients, sleep quality was not consistently poor. Pooled cross‐section regression analyses showed significant temporal relationships between quality of sleep and pain intensity such that a night of poor sleep was followed by a significantly more painful day. Pain during the day was not found to be a significant predictor of poor sleep on the following night. These results support previous findings that perceived quality of sleep following burn injury is poor. Moreover, they show a daily relationship between quality of sleep and acute burn pain in which poor sleep is linked to higher pain intensity during the day.

Sleep pathophysiology in posttraumatic stress disorder and idiopathic nightmare sufferers

BACKGROUND Nightmares are common in posttraumatic stress disorder (PTSD), but they also frequently occur in idiopathic form. Findings associated with sleep disturbances in these two groups have been inconsistent, and sparse for idiopathic nightmares. The aim of the present study was to investigate whether sleep anomalies in PTSD sufferers with frequent nightmares (P-NM) differ from those observed in non-PTSD, idiopathic nightmare (I-NM) sufferers and healthy individuals. METHODS Sleep measures were obtained from nine P-NM sufferers, 11 I-NM sufferers, and 13 healthy control subjects. All participants slept in the laboratory for two consecutive nights where electroencephalogram, electro-oculogram, chin and leg electromyogram, electrocardiogram, and respiration were recorded continuously. RESULTS Posttraumatic nightmare sufferers had significantly more nocturnal awakenings than did I-NM sufferers and control subjects. Elevated indices of periodic leg movements (PLMs) during rapid eye movement (REM) and non-REM sleep characterized both P-NM and I-NM sufferers. CONCLUSIONS Posttraumatic nightmare sufferers exhibit more nocturnal awakenings than do I-NM sufferers and control subjects, which supports the hypothesis of hyperarousal in sleep in PTSD sufferers; however, elevated PLM indices in both P-NM and I-NM sufferers suggest that PLMs may not be a marker of hyperarousal in sleep of PTSD sufferers. Rather, PLMs may be a correlate of processes contributing to intense negative dreaming.

What are the memory sources of dreaming

Investigators since Freud have appreciated that memories of the people, places, activities and emotions of daily life are reflected in dreams but are typically so fragmented that their predictability is nil. The mechanisms that translate such memories into dream images remain largely unknown. New research targeting relationships between dreaming, memory and the hippocampus is producing a new theory to explain how, why and when we dream of waking life events.

Immediate and delayed incorporations of events into dreams: further replication and implications for dream function

The incorporation of memories into dreams is characterized by two types of temporal effects: the day‐residue effect, involving immediate incorporations of events from the preceding day, and the dream‐lag effect, involving incorporations delayed by about a week. This study was designed to replicate these two effects while controlling several prior methodological problems and to provide preliminary information about potential functions of delayed event incorporations. Introductory Psychology students were asked to recall dreams at home for 1 week. Subsequently, they were instructed to select a single dream and to retrieve past events related to it that arose from one of seven randomly determined days prior to the dream (days 1–7). They then rated both their confidence in recall of events and the extent of correspondence between events and dreams. Judges evaluated qualities of the reported events using scales derived from theories about the function of delayed incorporations. Average ratings of correspondences between dreams and events were high for predream days 1 and 2, low for days 3 and 4 and high again for days 5–7, but only for participants who rated their confidence in recall of events as high and only for females. Delayed incorporations were more likely than immediate incorporations to refer to events characterized by interpersonal interactions, spatial locations, resolved problems and positive emotions. The findings are consistent with the possibility that processes with circaseptan (about 7 days) morphology underlie dream incorporation and that these processes subserve the functions of socio‐emotional adaptation and memory consolidation.

Impact of Imagery Rehearsal Treatment on Distressing Dreams, Psychological Distress, and Sleep Parameters in Nightmare Patients

We investigated the impact of imagery rehearsal treatment (IRT) on nightmare frequency, psychological distress, and sleep quality using polysomnography (PSG). 12 chronic nightmare patients completed prospective dream logs, measures of psychological distress, and underwent PSG prior to and 8.5 weeks following a single IRT session. Post-treatment, significant reductions were observed in retrospective nightmare frequency (d = 1.06, p = .007), prospective bad dream frequency (d = 0.53, p = .03), and anxiety scores (d = 1.01, p = .004). Minimal sleep alterations were found post-IRT, and varied as a function of nightmare etiology. The results independently replicate the efficacy of IRT for alleviating disturbing dreams and psychological distress. Sleep improvement may occur later in the recovery process.

Interhemispheric EEG Coherence before and after Partial Callosotomy

Measures of interhemispheric EEG coherence during REM and NREM sleep reflect the functional connectivity of the right and left hemispheres mediated by the corpus callosum. Surface recordings of interhemispheric coherence in two patients reflected fairly accurately the degree of anatomical section produced by partial callosotomy. With further development, EEG coherence may prove useful as a noninvasive method for assessing interhemispheric integration under different physiological and experimental conditions.

Decreased Interhemispheric EEG Coherence during Sleep in Agenesis of the Corpus Callosum

Inter- and intrahemispheric EEG coherence was studied in 4 subjects with agenesis of the corpus callosum (ACC) and in 4 matched controls through different states of the sleep/wakefulness cycle. Interhemispheric coherence was calculated between homologous prefrontal, frontal, central, parietal and occipital electrode pairs whereas intrahemispheric coherence was calculated between all adjacent, unihemispheric electrode pairs. EEG samples were recorded from stage 2, stages 3 + 4 and stage REM sleep and the eyes closed waking state. Interhemispheric coherence measures indicated lower values for ACC subjects than for control subjects for most brain regions; the occipital cortex was least affected. These results further validate the interhemispheric coherence function as a measure of activity in the corpus callosum and suggest that occipital measures may index activity localized in the posterior commissure. Intrahemispheric coherence measures indicated very few differences between the two groups, a result consistent with the suggestion that there is no specialized intrahemispheric compensation in ACC.

Nightmares, Bad Dreams, and Emotion Dysregulation: A Review and New Neurocognitive Model of Dreaming

Nightmares—vivid, emotionally dysphoric dreams—are quite common and are associated with a broad range of psychiatric conditions. However, the origin of such dreams remains largely unexplained, and there have been no attempts to reconcile repetitive traumatic nightmares with nontraumatic nightmares, dysphoric dreams that do not awaken the dreamer, or with more normative dreams. Based on recent research in cognitive neuroscience, sleep physiology, fear conditioning, and emotional-memory regulation, we propose a multilevel neurocognitive model that unites waking and sleeping as a conceptual framework for understanding a wide spectrum of disturbed dreaming. We propose that normal dreaming serves a fear-extinction function and that nightmares reflect failures in emotion regulation. We further suggest that nightmares occur as a result of two processes that we term affect load—a consequence of daily variations in emotional pressures—and affect distress—a disposition to experience events with high levels of negative emotional reactivity.