Considering REM sleep-like stages among the traits defining cognitively complex lineages

Sleep stages resembling the REM and non-REM (NREM) phases observed in mammals and birds were recently found in other vertebrates, cephalopods, and euarthropods. REM sleep-like stages could mark a leap in cognitive evolution, by regulating the visuomotor elaboration that Coombs and Trestman deem essential for the cognitively complex lineages. The more widespread NREM sleep-like stages likely modulate metabolism and homeostasis of synaptic circuits.