Dissociative symptoms are notorious for their enigmatic, disparate nature encompassing excessive daydreaming, memory problems, absentmindedness, and impairments and discontinuities in perceptions of the self, identity, and the environment. The famous 19th century British neurologist Hughlings Jackson was the first to view dissociation as the uncoupling of normal consciousness, resulting in what he termed 'the dreamy state'. Recent studies have linked dissociative symptoms to vivid dreaming, nightmares, and objective sleep parameters (e.g., lengthening of REM sleep). Germane to this is the idea that in dissociative individuals, the waking state as compared to REM sleep may be marked by an increase in “fluid” and hyperassociative thinking.

Llewellyn has advanced a theory which posits that a progressive de-differentation of wake and dream states of consciousness eventually results in schizophrenia; a lesser degree of de-differentiation may have implications for dissociative symptoms. Because of the differences in neuromodulatory systems between waking and dreaming, the self and the world during dreaming differ. The perceived world during waking depends on making sense of external sensory input, which engenders a strong sense of external reality in which the ‘self and its inner-world’ exists. Self-organizing during waking and dreaming enables integration of the self and the world in both states. Accordingly, when a degree of loss of self-organization occurs, de-differentation of the waking and dreaming states may ensue, fostering a perception of loss of self, as occurs during episodes of depersonalization. Several authors have commented on the overlap between dissociative symptoms and psychotic–like experiences. Interestingly, a disturbance in the feeling of presence of the self situated in the world is considered as one of the hallmarks of the schizophrenic prodrome. This sense that the self is alienated from the experience manifests in various forms in schizophrenia and other conditions, most notably as depersonalization and derealization experiences, which are considered core dissociative symptoms.

Speculations about the relation between sleep and memory can be traced back to the early nineteenth century when the British psychologist David Hartley (1801) argued that dreaming might change the strength of associative memory links within the brain. Today, we know that sleep plays a crucial role in extracting meaning and in facilitating associative links with existing information (abstraction) so as to create more adaptive semantic networks. Sleep disturbances are not only associated with omission and commission errors, but also with memory fragmentation. Interestingly, higher dissociation scores were related to more temporal disintegration (i.e., memory deficits regarding the chronology of events). There is also an intimate connection between dissociation and the inability to forget emotional stimulus material. Sleep deprivation differentially affects memory for emotional stimuli. Specifically, it disrupts encoding and later retention of neutral and positive stimuli, but negative stimuli seem to be relatively immune to these effects. Accordingly, negative thoughts may infiltrate consciousness, thereby fostering further sleep disruption, dissociation, and other manifestations of psychopathology.

In sum, we welcome theoretical and empirical contributions on the linkage of consciousness, memory, and mental illness with a special interest for dissociative symptoms.

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