United States: Scientists from the Okinawa Institute of Science and Technology (OIST) and the University of Washington have conducted a study on the sleeping behaviour of octopuses (Octopus laqueus), revealing striking similarities to human sleep patterns. The research, published in Nature, sheds light on the origins and functions of sleep.
The team discovered that octopuses exhibit two-stage sleep, similar to humans. During the active phase of sleep, the brain activity and skin patterning of octopuses closely resemble their wakeful state. This finding aligns with the wake-like activity observed during rapid eye movement (REM) sleep in mammals.
To confirm that the octopuses were indeed asleep, researchers tested their response to physical stimuli and found that they required stronger stimulation during both the quiet and active stages of sleep compared to when awake. Furthermore, preventing sleep or disrupting the active phase resulted in more frequent entry into active sleep.
By examining the brain activity of octopuses during different sleep stages, scientists observed sleep spindles—characteristic brain wave patterns akin to those observed in non-REM sleep in humans. These sleep spindles occurred in areas associated with learning and memory, indicating a potential role in memory consolidation.
The research team also investigated the skin patterns of octopuses using ultra-high-resolution imaging. They found that during active sleep, the octopuses cycled through the same skin patterns they used when awake, suggesting a connection between sleep and camouflage behaviour. The similarities between active sleep and wakefulness in octopuses raise intriguing questions. One hypothesis suggests that octopuses may be refining their skin patterns during sleep to enhance camouflage or maintain pigment cells. Another theory proposes that they may be reliving and learning from their waking experiences, similar to dreaming in humans.
The study’s senior author, Professor Sam Reiter, emphasized the need for further investigation to determine the exact explanation behind these phenomena. The research opens up new avenues for exploring the complex nature of sleep across different species and provides valuable insights into the evolution and function of this vital biological process.