Theoretical reviewNeural correlates of insight in dreaming and psychosis
Introduction
Rapid eye movement (REM) sleep is the sleep stage associated with the most vivid and intense dreams. These internally generated perceptions and emotions typically show many cognitive peculiarities, with a bizarre plot, delusional thought, and a complete lack of insight into the true state of the subject. In this regard, dreaming resembles the psychosis of mental illness such as schizophrenia, characterized by hallucinations, loosening of associations, incongruity of personal experience, and a loss of self-reflective capacity [1], [2]: both the psychotic patient and the dreamer fail to discern self-generated from non-self-generated percepts, and uncritically accept bizarre experiences as real [3].
The idea that dreaming can indeed serve as a model for psychosis has a long and honourable tradition: Kant [4] likened the madman to a waking dreamer, Schopenhauer [5] considered the dream a brief madness and madness a long dream, and also modern psychiatrists such as Bleuler, Kraepelin, Freud or Jung stressed the similarities between dreaming and psychosis [6]. While these historical proposals to consider dreaming as a model for psychosis are notoriously speculative, they are supported by recent studies of dream phenomenology: dream reports of healthy subjects include more quasipsychotic experiences than their reports of experiences during wakefulness [7], and striking similarities in cognitive bizarreness measures were found between the waking thought of psychotic patients and dream reports of either patients or healthy controls [6], [8], ∗[9], [10], [11], [12]. In other words, whereas healthy subjects experience strong fluctuations of bizarre and hallucinated cognitive elements across the sleep–wake cycle, psychotic patients continuously experience such dream-like mentations during both waking and dreaming [13]. Interestingly, also during wakefulness, psychotic patients consider their dream reports as being less bizarre than healthy controls do, despite a similar density of bizarre elements as scored by external judges [14]. In addition, similarities between REM sleep and schizophrenia can also be observed at the neurobiological level [15], in particular noradrenergic demodulation was proposed to contribute to the cognitive disturbances that occur during dreaming and psychosis [16].
Section snippets
Insight in dreaming and psychosis
One of the most interesting aspects of the dreaming–psychosis model is the issue of insight: between 50 and 80% of the patients diagnosed with schizophrenia have poor insight into the presence of their disorder [17], probably due to ineffective self-reflection processes [18]. Since such deficits are thought to lead to more relapses and rehospitalisations and poorer therapy success in general [19], the concept of insight is becoming an increasingly important area of investigation in
The dreaming brain
Dream-like mental activity can be observed during all sleep stages, however REM sleep dreams are particularly vivid and intense. The specific phenomenal characteristics of dreaming have frequently been associated with neural activation patterns observed during REM sleep. For example, during normal REM sleep, higher visual and motor areas show strong metabolic activity [36], [37], which is in line with visuomotor hallucinations as the hallmark of typical dreaming [38]. Also the amygdala, medial
The lucid brain
While lucid dreaming is characterized by all coarse electroencephalogram (EEG) features of REM sleep according to classical sleep stage scoring [42], brain activity during lucid REM sleep shows distinctive changes compared to non-lucid REM sleep. Fig. 1 shows the increased EEG activation that was observed over the right dorsolateral prefrontal cortex during lucid dreaming [34]. In this study, three subjects out of 20 undergraduate students participating in three months of lucidity training were
The psychotic brain
During recent years, an increasing number of approaches has shed light on the neural mechanisms underlying impaired insight in psychotic patients. Numerous neuropsychological studies on schizophrenia observed a relationship between insight deficits and impaired performance in cognitive tasks primarily mediated by the prefrontal cortex [49], [50].
Several neuroimaging studies confirmed an association of prefrontal brain areas with impaired insight in psychotic patients, however revealed also
Insight in dreaming and psychosis: neural similarities
On first sight, this short literature review presents a rather scattered picture, with a great variety of brain regions found to be involved in insight deficits in psychosis. However, the most robust findings seem to be prefrontal, medial parietal and cingulate cortex contributions underlying insight deficits in psychosis. Interestingly, grey matter volume reductions in frontal and parietal regions are not only state markers of insight deficits, but also have predictive value: In a longitudinal
Clinical implications
Since the majority of studies support the assumption that insight in schizophrenia is associated with compliance during treatment [19], interventions to promote insight are thought to be crucial for therapy success [20]. Insight deficits in psychosis have been targeted with a great variety of interventions, however there is still a paucity of reliable data on successful treatment options [84]. Interventions with at least some empirical support include pharmaceuticals [75], psychoeducation [85],
Limitations
While the large overlap between neural correlate of insight in dreaming and psychosis provides evidence for the dreaming–psychosis model, this confirmation cannot be generalized to all aspects of the model: the neural basis of self-reflection might be similar during dreaming and psychosis, however this similarity might theoretically be an exception, independent from the general validity of the model. Hence, other aspects of the model will have to be tested in further studies.
Furthermore, it
Conclusions
In conclusion, recent EEG and neuroimaging research shows that regions that have been related to psychotic insight deficits are highly activated in lucid compared to non-lucid dreaming. This fact empirically substantiates the analogy between the metacognitive impairments in psychosis and non-lucid dreaming. While research into lucid dreaming is currently limited by the rarity of the phenomenon, metacognitive training or other lucid dreaming induction methods might lead to new therapeutic
Disclosure
The authors declare no conflict of interest.
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