Sleep has been described in all branches of the animal kingdom, but slow-wave sleep (SWS) and paradoxical or rapid eye movement (REM) sleep have only been described in mammals, birds and reptiles. Cellular-resolution polysomnography in zebrafish revealed two major sleep signatures — termed slow bursting sleep and propagating wave sleep — that share features of SWS and REM sleep. The authors also found that melanin-concentrating hormone signalling (which is involved in mammalian sleep) regulates propagating wave sleep and the overall amount of sleep in zebrafish. These findings suggest that common neural sleep signatures might be present across all vertebrates.
Leung, L. C. et al. Neural signatures of sleep in zebrafish. Nature 571, 198–201 (2019)