do you dream in deep sleep or shallow sleep

Expanding on this previous work, we tested whether octopuses possess two stages of sleep behaviour. In octopus, this has been termed ‘active sleep’ (AS) and is accompanied by an increased arousal threshold, one of several criteria of sleep 15, 21. Sleeping cephalopods 17 have been observed to undergo rhythmic bouts of body twitches and rapid changes in skin patterning 6, 18, mediated by neural control of large populations of skin pigment cells (chromatophores) 19 among other specialized cell types 20. Octopuses are among the largest brained invertebrates and demonstrate a range of sophisticated behaviours 16, making them ideal for testing the generality of two-stage sleep.

If the functions ascribed to two-stage sleep are truly general, then one may expect to find neural and behavioural correlates of two-stage sleep widely among animals showing complex cognitive abilities. Vertebrate rapid eye movements (REMs) and slow wave sleep are characterized by a core set of behavioural and electrophysiological correlates, and proposed cognitive functions 13, 14, 15 while showing a rich diversity of species-specific features 15. The range of similarities with vertebrates indicates that aspects of two-stage sleep in octopuses may represent convergent features of complex cognition. During quiet sleep, these regions are relatively silent but generate LFP oscillations resembling mammalian sleep spindles 11, 12 in frequency and duration. LFP activity differs across brain regions, with the strongest activity during active sleep seen in the superior frontal and vertical lobes, anatomically connected regions associated with learning and memory function 7, 8, 9, 10. High-density electrophysiological recordings from the central brain reveal that the local field potential (LFP) activity during active sleep resembles that of waking. Computational analysis of active sleep skin patterning reveals diverse dynamics through a set of patterns conserved across octopuses and strongly resembling those seen while awake. We show that these bouts are homeostatically regulated, rapidly reversible and come with increased arousal threshold, representing a distinct ‘active’ sleep stage. ‘Quiet’ sleep in octopuses is rhythmically interrupted by approximately 60-s bouts of pronounced body movements and rapid changes in skin patterning and texture 6. 5) and have independently evolved large brains and behavioural sophistication. 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. While sleeping, many vertebrate groups alternate between at least two sleep stages: rapid eye movement and slow wave sleep 1, 2, 3, 4, in part characterized by wake-like and synchronous brain activity, respectively.

Do you dream in deep sleep or shallow sleep