Study
Cyclic alternation of quiet and active sleep states in the octopus
Medeiros, Sylvia L. S.; Paiva, Mizziara M. M.; Lopes, Paulo H.; Ribeiro, Sidarta; Leite, Tatiana S.
iScience, 2021
Octopuses were filmed around the clock. Periods of rest were classified by skin pattern, eye and arm movement, and responsiveness to stimuli was tested to confirm that rest states were genuinely sleep-like.
- Studied in
- Octopus insularis
- Sample size
- 4 captive octopuses filmed continuously
Rest alternated between a pale, still "quiet" state and brief episodes of rapid skin-colour change, eye movement and muscle twitching, recurring roughly every half hour or so.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Octopuses have two-stage sleep with an active phase superficially resembling vertebrate REM sleep.
How NatureHQ reads it
This is where "do octopuses dream?" comes from. What was shown is a cyclic active sleep state — the same *structure* as REM sleep, arrived at independently. Whether anything is experienced during it is not something a camera can answer, and the researchers say so. Four animals of one species.
- Four individuals.
- Behavioural classification without simultaneous brain recording.
- Structural similarity to REM sleep does not imply similar function or experience.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Cell PressPublished in a Cell Press journal.
doi.org/10.1016/j.isci.2021.102223
This reference was resolved automatically against Crossref and OpenAlex on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-09.