From REM sleep behaviour disorder to status dissociatus: Insights into the maze of states of being

Sleep is a coordinated process involving more or less simultaneous changes in sensory, motor, autonomic, hormonal, and cerebral processes. On the other hand, none of the changes occurring with sleep are invariably coupled to sleep. EEG synchrony, heat loss, sleep-related hormone secretion, and even REM-related motoneuron paralysis may occur independent of the parent state. In REM sleep behaviour disorder (RBD) the muscle tone of wakefulness intrudes into REM sleep, allowing the release of dream-enacting behaviours. Status dissociatus (SD) is a condition in which brain and mind are in disarray along the boundaries of sleep and wakefulness. The existence of such dissociated behaviours shows that they have separate neuronal control systems and indicates that the whole organization of sleep is an emergent property of the collective neuronal systems to synchronize. Insults to the brain can drastically alter the circuitries responsible for maintaining the integrity of wakefulness, NREM sleep, and REM sleep. As a consequence, the basic states of existence can become admixed and interchanged with striking disturbances of consciousness, brain electrophysiology, and the behavioural and polygraphic expression of sleep and wakefulness. The evolution of RBD into SD may result from a disarray of (brainstem) structures that orchestrate the whole brain wake–sleep conditions, but with preserved discrete systems and dissociable strategies to still place navigation in wake and sleep. Advances in the fields of genetics, neuroimaging, and behavioural neurology will expand the understanding of the mechanisms underlying the organization of the states of being along with their somatic/behavioural manifestations.