Cephalopod Resting Cycles Provide Evolutionary Insights

The mind of the octopus has fascinated scientists for decades. The octopus has been hypothesized to be one of the most resourceful and intelligent creatures in the animal kingdom, with a relatively large brain size to accompany its eight arms and three hearts. The shape-shifting and camouflaging abilities, alongside a sharp intellect for uncovering patterns and puzzles, makes this cephalopod mind critical in uncovering details of cognitive evolution. To shed insight into the relationship between cognition and sleep, a recent paper published in iScience investigated the sleep cycles of octopuses, revealing two distinct sleeping stages: a “quiet stage” and an “active stage.” 

Through observation of four wild-caught octopuses, Octopus insularis, neuroscientist Sylvia Medeiros and her team uncovered patterns in sleeping behaviors and physiological responses. Using video recordings, the team detected changes in skin color, texture, and eye movements during the two distinct patterns of sleep. The “quiet stage” was accompanied by pale skin and closed pupils, while in “active sleep,” the octopuses exhibited changing color and texture patterns and rapid eye movements. “Quiet sleep” was found to be much more common, lasting for seven minute increments, and active sleep occurred periodically in approximately 40 second increments. 

This ultradian sleep cycle, i.e. one that occurs repeatedly throughout a 24-hour day, is strikingly similar to the patterns of rapid eye movement (REM) and non-REM sleep seen in humans. The discovery of similar sleeping patterns provides an identifiable link between vertebrates and invertebrates, despite the branching of evolutionary pathways and drastic differences in brain anatomy and tissue organization. These sleeping patterns point to an origin in a common ancestor existing prior to the divergence of invertebrate and vertebrate species approximately 500 million years ago. Further investigations examining the electrophysiology and function of sleep will likely uncover greater evolutionary similarities related to memory storage and cognitive function. While human and celelophod development have long been considered separate evolutionary tracks, investigations in sleep cycles show that we might have greater connections to these creatures of the deep sea than we thought. 

Lead author Sylvia Lima de Souza Medeiros is a neuroscience graduate student at the Brain Institute of the Federal University of Rio Grande do Norte (UFRN) where she is a member of the Laboratory of Memory, Sleep and Dreams. Her research centers on sleep and learning in octopuses. 

Managing Correspondent: Samantha Tracy

Press Article: “Octopus sleep includes a frenzied, colorful, ‘active’ stage”

Journal Article: “Cyclic alternation of quiet and active sleep states in the octopus.”

Photo Credit: Pixabay