Very interesting (and very short) article: See an Octopus Change Color as It Sleeps, Perchance Dreams
According to Mather, one of the theories behind sleep is for an organism to rehearse and solidify traces in the brain from experiences of the previous day. Octopus brains do the same kind of thing. “If this central experience is ‘dreaming,’ and our dreaming is often linked to what has happened before, then octopuses might dream,” she says.
The only cephalopod with a proven penchant for dreaming is probably the cutest. A 2012 study led by Marcos G. Frank, now a neuroscientist at Washington State University Health Sciences Spokane, discovered that sleeping cuttlefish demonstrate a form of rapid eye movement (REM), the same stage of sleep that gives us our dreams, distinguished by the spontaneous activation of brain cells, going off like fireflies in a forest. For a cephalopod, this manifests in frantic eye movements under closed lids (octopuses: they’re just like us) or erratic shifts in skin coloration (or not). In Frank’s study, the sleeping cuttlefish’s chromatophores recombined into recognizable patterns, just like ones they displayed while awake. He believes this might be analogous to the weirdly familiar patchwork of human dreams. “This video is the best evidence I have ever seen that this particular cephalopod has a sleep-state similar to what we saw in cuttlefish,” Frank says of the Caribbean two-spot octopus.