No phylogeny without ontogeny-a comparative and developmental search for the sources of sleep-like neural and behavioral rhythms

A comprehensive review is presented of reported aspects and putative mechanisms of sleep-like motility rhythms throughout the animal kingdom. It is proposed that ＇rapid eye movement （REM） sleep＇ be regarded as a special case of a distinct but much broader category of behavior, ＇rapid body movement （RBM） sleep＇, defined by intrinsically- generated and apparently non-purposive movements. Such a classification completes a 2 2 matrix defined by the axes sleep versus waking and active versus quiet. Although ＇paradoxical＇ arousal of forebrain electrical activity is restricted to warm-blooded vertebrates, we urge that juvenile or even infantile stages of development be investigated in cold-blooded animals, in view of the many reports of REM-like spontaneous motility （RBMs） in a wide range of species during sleep. The neurophysiological bases for motorically active sleep at the brainstem level and for slow-wave sleep in the forebrain appear to be remarkably similar, and to be subserved in both cases by a primitive diffuse mode of neuronal organization. Thus, the spontaneous synchronous burst discharges which are characteristics of the sleeping brain can be readily simu- lated even by highly unstructured neural network models. Neuromotor discharges during active sleep appear to reflect a hierarchy of simple relaxation oscillation mechanisms, spanning a wide range of spike-dependent relaxation times, where- as the periodic alternation of active and quiet sleep states more likely results from the entrainment of intrinsic cellular rhythms and/or from activity-dependent homeostatic changes in network excitability.

Perchance to dream? Primordial motor activity patterns in vertebrates from fish to mammals: their prenatal origin, postnatal persistence during sleep, and pathological reemergence during REM sleep behavior disorder

An overview is presented of the literature dealing with sleep-like motility and concomitant neuronal activity patterns throughout the life cycle in vertebrates, ectothermic as well as endothermic. Spontaneous, periodically modulated, neurogenic bursts of non-purposive movements are a universal feature of larval and prenatal behavior, which in endothermic animals （i.e. birds and mammals） continue to occur periodically throughout life. Since the entire body musculature is involved in ever-shifting combinations, it is proposed that these spontaneously active periods be designated as ＇rapid-BODY-movement＇ （RBM） sleep. The term ＇rapid-EYE- movement （REM） sleep＇, characterized by attenuated muscle contractions and reduced tonus, can then be reserved for sleep at later stages of development. Mature stages of development in which sustained muscle atonia is combined with ＇paradoxical arousal＇ of cortical neuronal firing patterns indisputably represent the evolutionarily most recent aspect of REM sleep, but more research with ectothermic vertebrates, such as fish, amphibians and reptiles, is needed before it can be concluded （as many prematurely have） that RBM is absent in these species. Evidence suggests a link between RBM sleep in early development and the clinical condition known as ＇REM sleep behavior disorder （RBD）＇, which is characterized by the resurgence of periodic bouts of quasi-fetal motility that closely resemble RBM sleep. Early developmental neuromotor risk factors for RBD in humans also point to a relationship between RBM sleep and RBD.

Call it sleep-what animals without backbones can tell us about the phylogeny of intrinsically generated neuromotor rhythms during early development

A comprehensive overview is presented of the literature dealing with the development of sleep-like motility and neuronal activity patterns in non-vertebrate animals. It has been established that spontaneous, periodically modulated, neurogenic bursts of movement appear to be a universal feature of prenatal behavior. New empirical data are presented showing that such ＇seismic sleep＇ or ＇rapid-body-movement＇ bursts in cuttlefish persist for some time after birth. Extensive ontogenetic research in both vertebrates and non-vertebrates is thus essential before current hypotheses about the phylogeny of motorically active sleep-like states can be taken seriously.