Abstract: Background: The incubus phenomenon is a paroxysmal sleep-related disorder characterized by compound hallucinations experienced during brief phases of (apparent) wakefulness. The condition has an almost stereotypical presentation, characterized by a hallucinated being that exerts pressure on the thorax, meanwhile carrying out aggressive and/or sexual acts. It tends to be accompanied by sleep paralysis, anxiety, vegetative symptoms, and feelings of suffocation. Its prevalence rate is unknown since, in prior analyses, cases of recurrent isolated sleep paralysis with/without an incubus phenomenon have been pooled together. This is unfortunate, since the incubus phenomenon has a much greater clinical relevance than isolated sleep paralysis. Methods: PubMed, Embase, and PsycINFO were searched for prevalence studies of the incubus phenomenon and a meta-analysis was performed. Results: Of the 1,437 unique records, 13 met the inclusion criteria, reporting on 14 (k) independent prevalence estimates (total N = 6,079). The pooled lifetime prevalence rate of the incubus phenomenon was 0.19 (95% confidence interval [CI] = 0.14 to 0.25, k = 14, N = 6,079) with heterogeneous estimates over different samples. In selected samples (e.g., patients with a psychiatric disorder, refugees, and students), prevalence rates were nearly four times higher (0.41, 95% CI = 0.25 to 0.56, k = 4, n = 1,275) than in the random samples (0.11, 95% CI = 0.08 to 0.14, k = 10, n = 4,804). This difference was significant (P < 0.001). Conclusions: This review and meta-analysis yielded a lifetime prevalence of the incubus phenomenon in the general population of 0.11 and, in selected samples, of 0.41. This is slightly higher than the prevalence rates in previous analyses that included cases of recurrent isolated sleep paralysis without an incubus phenomenon. Based on the condition’s robust clinical presentation and the relatively high prevalence rates, we advocate inclusion of the incubus phenomenon as a diagnostic category in major classifications such as the International Classification of Diseases and Related Health Problems (ICD) and the Diagnostic and Statistical Manual of Mental Disorders (DSM). Recommendations are also made for clinical practice and future research.
Here is a new paper on verbal perseveration errors in nightmare-prone individuals:
Elevated perseveration errors on a verbal fluency task in
frequent nightmare recallers: a replication
MICHELLE CARR, KADIA SAINT-ONGE, CLOE BLANCHETTE-CARRIERE, TYNA PAQUETTE and TORE NIELSEN
A recent study reported that individuals recalling frequent idiopathic
nightmares (NM) produced more perseveration errors on a verbal fluency
task than did control participants (CTL), while not differing in overall verbal
fluency. Elevated scores on perseveration errors, an index of executive
dysfunction, suggest a cognitive inhibitory control deficit in NMparticipants.
The present study sought to replicate these results using a French-speaking
cohort and French language verbal fluency tasks. A phonetic verbal fluency
task using three stimulus letters (P, R, V) and a semantic verbal fluency task
using two stimulus categories (female and male French first names) were
administered to 23 participants with frequent recall of NM (≥2 NMper week,
mean age = 24.4 4.0 years), and to 16 CTL participants with few
recalled NM (≤ 1 NM per month, mean age = 24.5 3.8 years). All
participants were French-speaking since birth and self-declared to be in
good mental and physical health apart from their NM. As expected, groups
did not differ in overall verbal fluency, i.e. total number of correct words
produced in response to stimulus letters or categories (P = 0.97). Furthermore,
groups exhibited a difference in fluency perseveration errors, with the
NM group having higher perseveration than the CTL group (P = 0.03,
Cohen’s d = 0.745). This replication suggests that frequent NM recallers
have executive inhibitory dysfunction during a cognitive association task
and supports a neurocognitive model which posits fronto-limbic impairment
as a neural correlate of disturbed dreaming.
A novel Differential Susceptibility framework for the study of nightmares: Evidence for trait sensory processing sensitivity
Michelle Carr & Tore Nielsen
Research on nightmares has largely focused on the nightmare itself and its associated negative consequences, framing nightmare sufferers as victims of a diathesis-stress induced form of psychopathology. However, there is evidence that frequent nightmare recallers are sensitive to a wide range of sensory and emotional experiences, and report vivid, bizarre and even intensely positive dream and daydream experiences. We propose sensory processing sensitivity as a novel trait marker that underlies the unique symptoms and imaginative richness found in nightmare-prone individuals. Sensory processing sensitivity describes an increased emotional reactivity, greater depth of processing, and subtle awareness of environmental stimuli—it is a ‘for better and for worse’ trait that is associated with positive outcomes in conditions of support, but also confers a tendency to be easily overwhelmed by stressors and adversity. This novel approach places nightmare-prone individuals within the broader framework of Differential Susceptibility and raises the possibility that they may benefit especially from supportive environments—a possibility that is particularly relevant for developing future treatment approaches.