Wake-like skin patterning and neural activity during octopus sleep.

While sleeping, many vertebrate groups alternate between at least two sleep stages: rapid eye movement and slow wave sleep, in part characterized by wake-like and synchronous brain activity, respectively. Here we delineate neural and behavioural correlates of two stages of sleep in octopuses, marine invertebrates that evolutionarily diverged from vertebrates roughly 550 million years ago (ref. ) and have independently evolved large brains and behavioural sophistication.