# Sleep, Two-Stage Sleep, and Possible Dreaming in Octopuses

> Part IV: Inner Life, Sentience & Ethics · Chapter 9 of 17 — The Octopus Mind
> Canonical: https://octopuscognition.org/sections/sleep-two-stage-sleep-and-possible-dreaming-in-octopuses/

## In brief

Sleep in octopuses was first established behaviorally, then—remarkably—shown to have a two-stage architecture rivaling the vertebrate distinction between non-REM and REM sleep. The foundational work (Brown et al., 2006; Meisel et al., 2011) demonstrated that Octopus vulgaris meets the classical behavioral criteria for sleep: a reversible quiescent state…

Sleep in octopuses was first established behaviorally, then—remarkably—shown to have a two-stage architecture rivaling the vertebrate distinction between non-REM and REM sleep. The foundational work (Brown et al., 2006; Meisel et al., 2011) demonstrated that *Octopus vulgaris* meets the classical behavioral criteria for sleep: a reversible quiescent state with reduced activity, elevated arousal thresholds during quiet periods, and homeostatic rebound when quiescence is prevented. This satisfied the three-part behavioral definition of sleep (raised arousal threshold, rapid reversibility, and rebound after deprivation) without any need for a vertebrate-style cortex.

The two-stage discovery came from Sylvia Medeiros, Sidarta Ribeiro, and colleagues at the Brain Institute (UFRN, Brazil), published as Medeiros/Sampaio et al. (2021, *iScience*). Video-recording four adult *Octopus insularis*, they quantified a cyclic alternation between "quiet sleep" (QS)—pale, uniform skin, closed slit-pupils, stillness, median episode ~415 s (~6.9 min)—and a briefer "active sleep" (AS) phase (median ~40.8 s) of dynamic chromatophore-driven skin color and texture changes, rapid eye movements, sucker and mantle twitches, and quickened breathing. Critically, they demonstrated AS is true sleep, not waking: arousal-threshold tests using visual stimuli showed the longest response latencies and highest non-response rates during AS (median ~32 s vs. ~6 s in QS and ~4 s alert; p ≈ 2.2×10⁻¹⁶). AS almost always followed a long bout of QS (~82% of the time) and recurred with a periodicity clustered around 30–40 minutes. The behavioral resemblance to REM—twitches, eye movements, high arousal threshold—prompted cautious speculation that octopuses might experience something dream-like, while the authors stressed the cephalopod and vertebrate brains are non-homologous, making this convergent rather than inherited.

The decisive neural evidence came from Aditi Pophale, Sam Reiter, and colleagues at the Okinawa Institute of Science and Technology (OIST), published in *Nature* (Pophale et al., 2023). Using *Octopus laqueus* and Neuropixels probes in the central (supra-oesophageal) brain, with brain regions localized via CUBIC tissue clearing and light-sheet microscopy registered to a 3D atlas, they found that local field potential (LFP) activity during AS resembles waking. The superior frontal and vertical lobes—regions homologous in function to learning/memory circuits—showed the strongest AS activity, with the superior frontal lobe generating prominent ~30 Hz oscillations and the vertical lobe producing large (~700 μV) low-frequency waveforms; waking and AS LFP correlated strongly (Pearson R ≈ 0.74 low-frequency, 0.95 high-frequency). Strikingly, during QS the superior frontal lobe produced 12–18 Hz oscillatory events lasting up to ~1 s that resemble mammalian sleep spindles in frequency and duration—often with no visible behavioral correlate.

Pophale et al. also refined the timing: AS bouts recurred roughly hourly, each lasting ~60 s (75 ± 28 s), interleaved with QS bouts (~50 min); over a night at 22°C animals showed ~10 active bouts and ~12 QS bouts, with the interval temperature-dependent (a 1°C rise shortened intervals by ~5 min). Their sleep-deprivation experiment is the strongest functional evidence: keeping animals awake ~2 days produced a significant rebound—more frequent active bouts on the two following nights (P = 0.0065 and P = 0.0216, Wilcoxon)—establishing AS as a homeostatically regulated, essential sleep stage, not incidental restlessness.

The most provocative finding concerns possible dreaming. Using 8K video and a VGG-19 neural-network analysis of skin patterning, the team found AS skin dynamics rapidly cycle through the very same patterns octopuses deploy while awake and camouflaging—suggesting a "replay" or offline refinement of skin-pattern motor control, loosely analogous to rodent hippocampal replay or the structured head-direction activity seen during mammalian REM. Whether this constitutes dreaming remains unknowable; as Reiter and others emphasize, "we cannot ask the octopus."

Context from cuttlefish reinforces convergence: Frank et al. (2012) first reported a REM-like state in senescing *Sepia officinalis*, and Iglesias, Frank et al. (2019, *J. Exp. Biol.*) documented its cyclic nature (~2.4 min REM-like bouts alternating with ~34 min quiescence). A separate biorxiv preprint (Medeiros et al., 2023) reported bizarre "abnormal behavioral episodes" in senescing *O. insularis*—possible parasomnias or "nightmares"—though this remains anecdotal and unreviewed. The overarching interpretation: octopuses and mammals, whose last common ancestor lived ~550 million years ago, independently evolved two-stage sleep, implying the biphasic architecture serves something deeply fundamental.

**Striking / counterintuitive:**
- Active-sleep LFP brain activity in the octopus is nearly indistinguishable from waking activity (Pearson R up to 0.95 in high-frequency bands), yet arousal thresholds are highest during this stage.
- Quiet sleep contains 12–18 Hz oscillatory events lasting ~1 s that resemble mammalian sleep spindles—strikingly convergent given ~550 million years of separate evolution and no homologous brain structures.
- During active sleep, octopuses rapidly cycle their skin through the exact camouflage patterns they use while awake, hinting at offline 'replay' or rehearsal of skin-pattern control.
- Sleep-deprived octopuses rebound specifically by increasing active-sleep bouts, proving the REM-like stage is homeostatically defended and essential, not incidental.
- Active-sleep interval timing is temperature-dependent: a 1°C rise shortens the cycle by roughly 5 minutes.
- A preprint reports bizarre 'nightmare-like' abnormal episodes in senescing octopuses, though this is anecdotal.

**Open questions:**
- Do octopuses subjectively experience anything dream-like during active sleep, or is the skin-pattern 'replay' purely offline motor maintenance with no phenomenology? This is likely unanswerable with current methods.
- Is the skin-pattern cycling during active sleep true memory replay (like hippocampal replay) or stochastic churn through the motor repertoire?
- What is the mechanistic function of the sleep-spindle-like 12–18 Hz waveforms in quiet sleep—memory consolidation, as in mammals?
- Given non-homologous brains, is two-stage sleep a case of deep convergent evolution driven by shared computational constraints, or independent solutions that merely look alike?
- Do young, healthy octopuses show the same 'abnormal'/parasomnia-like episodes, or are those artifacts of senescence and captivity?
- How generalizable are findings across octopus species (O. insularis, O. laqueus, O. vulgaris) and to other coleoid cephalopods?

*Key researchers/labs: Sam Reiter (Computational Neuroethology Unit, OIST), Aditi Pophale (OIST, co-first author), Sylvia Medeiros (Brain Institute, UFRN Brazil), Sidarta Ribeiro (Brain Institute, UFRN), Marcos G. Frank (Washington State University; cuttlefish REM-like sleep), Teresa L. Iglesias, Ruth A. Byrne / David Meisel (early octopus sleep behavior), E. R. Brown (Stazione Zoologica Naples).*

### Key papers
- **Aditi Pophale, Kazumichi Shimizu, Tomoyuki Mano, Leenoy Meshulam, Sam Reiter, et al. (2023).** *Wake-like skin patterning and neural activity during octopus sleep.* Nature — Neuropixels recordings show active-sleep brain activity resembles waking and QS contains sleep-spindle-like waveforms; deprivation triggers rebound, and skin patterns replay waking camouflage—key evidence for a REM-like, possibly dream-like stage.
- **Sylvia L. de S. Medeiros, Mizziara M. M. de Paiva, Paulo H. Lopes, Sidarta Ribeiro, et al. (Sampaio group) (2021).** *Cyclic alternation of quiet and active sleep states in the octopus.* iScience — First to define two-stage octopus sleep (quiet vs active) in O. insularis, with arousal-threshold data proving active sleep is genuine sleep and speculation on dreaming.
- **Marcos G. Frank, R. J. Waldrop, M. Dumoulin, et al. (2012).** *A preliminary analysis of sleep-like states in the cuttlefish Sepia officinalis.* PLOS ONE — First report of a REM-like state in a cephalopod (senescing cuttlefish), establishing the cross-cephalopod precedent for REM-like sleep.
- **Teresa L. Iglesias, Marcos G. Frank, et al. (2019).** *Cyclic nature of the REM sleep-like state in the cuttlefish Sepia officinalis.* Journal of Experimental Biology — Documented cyclic ~2.4 min REM-like bouts alternating with ~34 min quiescence, showing periodic two-stage structure in cuttlefish.
- **David M. Meisel, Ruth A. Byrne, et al. (2011).** *Contribution of the visual system of the octopus to determination of sleep-like behavior.* Journal of Experimental Marine Biology — Helped establish behavioral sleep criteria (arousal threshold, reversibility) in Octopus vulgaris.
- **E. R. Brown, S. Piscopo, R. De Stefano, A. Giuditta (2006).** *Brain and behavioural evidence for rest-activity cycles in Octopus vulgaris.* Behavioural Brain Research — Foundational demonstration of circadian rest-activity cycles and quiescent behavioral sleep in octopus.

## Resolved source links

- [Wake-like skin patterning and neural activity during octopus sleep.](https://doi.org/10.1038/s41586-023-06203-4) — DOI 10.1038/s41586-023-06203-4
- [Cyclic alternation of quiet and active sleep states in the octopus.](https://doi.org/10.1016/j.isci.2021.102223) — DOI 10.1016/j.isci.2021.102223
- [A preliminary analysis of sleep-like states in the cuttlefish Sepia officinalis.](https://doi.org/10.1371/journal.pone.0038125) — DOI 10.1371/journal.pone.0038125
- [Cyclic nature of the REM sleep-like state in the cuttlefish Sepia officinalis.](https://doi.org/10.1242/jeb.174862) — DOI 10.1242/jeb.174862
- [Contribution of the visual system of the octopus to determination of sleep-like behavior.](https://search.crossref.org/?q=Contribution%20of%20the%20visual%20system%20of%20the%20octopus%20to%20determination%20of%20sleep-like%20behavior.)
- [Brain and behavioural evidence for rest-activity cycles in Octopus vulgaris.](https://doi.org/10.1016/j.bbr.2006.05.009) — DOI 10.1016/j.bbr.2006.05.009

## Related trails

- [The Inner Life Trail](https://octopuscognition.org/trails/inner-life/index.md): What can science responsibly say about octopus experience?