Study
Cetacean sleep: an unusual form of mammalian sleep
Lyamin, Oleg I.; Manger, Paul R.; Ridgway, Sam H.; Mukhametov, Lev M.; Siegel, Jerome M.
Neuroscience & Biobehavioral Reviews, 2008
A synthesis of electroencephalographic and behavioural sleep studies in dolphins, killer whales and belugas, covering the structure of cetacean sleep, its distribution between brain hemispheres, and its development in calves.
- Studied in
- Tursiops truncatus, Orcinus orca, Delphinapterus leucas
- Sample size
- synthesis of EEG and behavioural sleep recordings across cetaceans
Cetaceans sleep one cerebral hemisphere at a time, with the eye opposite the sleeping hemisphere closed, allowing continuous swimming and surfacing to breathe. REM sleep is minimal or absent by the usual criteria. Newborn calves and their mothers show almost no conventional sleep for the first weeks of life.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Unihemispheric slow-wave sleep is an adaptation to obligate voluntary breathing and continuous movement, and represents a genuinely different solution to sleep from that of land mammals.
How NatureHQ reads it
This is the cleanest available answer to "do dolphins sleep", and it dissolves the question rather than answering yes or no. A dolphin is never fully asleep and never fully awake — half its brain rests while the other half swims, watches and surfaces. The absence of measurable REM is the genuinely puzzling part, since REM is near-universal in mammals and is often tied to memory consolidation in exactly the sort of animal you would expect to need it.
- Overwhelmingly captive animals; wild sleep is very hard to record.
- REM detection depends on criteria developed for land mammals and may simply not transfer.
- Small numbers of individuals across a handful of species.
Recording half a brain asleep while the other half swims
A dolphin has to surface to breathe, and breathing in a cetacean is voluntary. How does an animal like that sleep at all?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/j.neubiorev.2008.05.023
This reference was resolved automatically against Crossref on 2026-08-11.
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