Study

Slow waves, sharp waves, ripples, and REM in sleeping dragons

Shein-Idelson, Mark; Ondracek, Janie M.; Liaw, Hua-Peng; Reiter, Sam; Laurent, Gilles

Science, 2016

Peer-reviewedcontrolled laboratory experimentlaboratory

What they did

Electrodes implanted in the brains of bearded dragons recorded activity across whole nights, alongside video of eye movement. The recordings were analysed for the alternation between slow-wave and low-amplitude fast states that defines mammalian and avian sleep architecture.

Studied in: Pogona vitticeps
Sample size: 5 bearded dragons with implanted electrodes

What they found

The lizards alternated between two distinct sleep states throughout the night, one with slow waves and sharp-wave ripples and one with low-amplitude activity and eye movements. The cycle was far faster than in mammals — around 80 seconds against roughly 90 minutes in humans — and much more regular.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Two-state sleep resembling non-REM and REM occurs in a reptile, suggesting the architecture is older than the mammal–bird split rather than having evolved twice.

How NatureHQ reads it

What makes this worth including is the timing. A reptile cycling every 80 seconds looks like the mammalian pattern in structure and nothing like it in tempo, which is a useful warning against reading human sleep stages onto other animals. The states are analogous; the experience they correspond to is not something the recording can tell us about.

Limitations

Five animals of one species, in a laboratory, with implanted electrodes.
Whether the reptile states are homologous to the mammalian ones or convergent is not resolved by the recording alone.
Naming the states REM and non-REM imports assumptions the data do not establish.