oceany: Sleep in animals

Evidence: 100 • authority: 72

Sleep is broadly considered a biological necessity in virtually all animals. The large majority of such taxa with documented sleep physiology are bilaterians, though there is increasing evidence of sleep or sleep-like states in non-bilaterians such as Cassiopea jellyfish and hydra (both cnidarians), and sponges. The various criteria which biologists use to define sleep states have been observed in all other animal phyla, often with profound variation in function. In all of these taxa except sponges, regulation of sleep is documented to involve genes whose transcription oscillates with time, known as circadian or clock genes. These genes and the gene networks they regulate give rise to the i…

Evidence: 64 • authority: 92

Evolution of canonical circadian clock genes underlies unique sleep strategies of marine mammals for secondary aquatic adaptation.. To satisfy the needs of sleeping underwater, marine mammals, including cetaceans, sirenians, and pinnipeds, have evolved an unusual form of sleep, known as unihemispheric slow-wave sleep (USWS), in which one brain hemisphere is asleep while the other is awake. All aquatic cetaceans have only evolved USWS without rapid eye movement (REM) sleep, whereas aquatic sirenians and amphibious pinnipeds display both bihemispheric slow-wave sleep (BSWS) and USWS, as well as REM sleep. However, the molecular genetic changes underlying USWS remain unknown. The present study…

Evidence: 59 • authority: 72

Cetaceans are marine mammals belonging to the infraorder Cetacea (), a secondarily aquatic clade under the order Artiodactyla that include whales, dolphins, porpoises and extinct groups such as Basilosaurus. Most cetaceans live in marine environments, particularly the pelagic zone, but some reside solely in brackish or fresh water. Having a cosmopolitan distribution, they can be found in some rivers and all of Earth's oceans. Many species migrate seasonally over vast ranges for food advantages. Key characteristics of cetaceans are their fully aquatic life cycle, streamlined, fish-like body shape, the need to periodically surface and breathe air, and exclusively carnivorous diet. Some cetace…

Evidence: 44 • authority: 92

Adaptive changes in BMAL2 with increased locomotion associated with the evolution of unihemispheric slow-wave sleep in mammals.. Marine mammals, especially cetaceans, have evolved a very special form of sleep characterized by unihemispheric slow-wave sleep (USWS) and a negligible amount or complete absence of rapid-eye-movement sleep; however, the underlying genetic mechanisms remain unclear. Here, we detected unique, significant selection signatures in basic helix-loop-helix ARNT like 2 (BMAL2; also called ARNTL2), a key circadian regulator, in marine mammal lineages, and identified two nonsynonymous amino acid substitutions (K204E and K346Q) in the important PER-ARNT-SIM domain of cetacea…

Evidence: 44 • authority: 72

The neuroscience of sleep is the study of the neuroscientific and physiological basis of the nature of sleep and its functions. Traditionally, sleep has been studied as part of psychology and medicine. The study of sleep from a neuroscience perspective grew to prominence with advances in technology and the proliferation of neuroscience research from the second half of the twentieth century. The importance of sleep is demonstrated by the fact that every day animals spend hours of their time in sleep, and that sleep deprivation can have disastrous effects ultimately leading to death in animals. For a phenomenon so important, the purposes and mechanisms of sleep are only partially understood,…

Evidence: 44 • authority: 72

Unihemispheric slow-wave sleep (USWS) is sleep where one half of the brain rests while the other half remains alert. This is in contrast to normal sleep where both eyes are shut and both halves of the brain show unconsciousness. In USWS, also known as asymmetric slow-wave sleep, one half of the brain is in deep sleep, a form of non-rapid eye movement sleep and the eye corresponding to this half is closed while the other eye remains open. When examined by electroencephalography (EEG), the characteristic slow-wave sleep tracings are seen from one side while the other side shows a characteristic tracing of wakefulness. The phenomenon has been observed in a number of terrestrial, aquatic and av…

Evidence: 38 • authority: 80

Evidence: 36 • authority: 92

The Sentinel Sleep Theory: Unweaving the biological function of REM sleep.. The biological function of Rapid Eye Movement (REM) sleep remains one of neuroscience's great mysteries. In this theoretical research paper, I present the evolutionary theory that explains why REM sleep exists. I demonstrate that REM sleep functions to heighten brain alertness to significantly mitigate the high vulnerability inherent in non‑REM sleep-especially in deep sleep. Every organism with a nervous system must undergo non-REM sleep, a necessity that accompanies a negative and potentially lethal consequence: a higher risk of dying. Because non‑REM sleep substantially reduces alertness and increases the death r…