In recent years, science has made significant discoveries in the study of sleep in various animals. However, a recent study published in Nature drew particular attention to the sleep activity of octopuses. Scientists found that these sea creatures have an “active sleep” phase, which resembles the rapid sleep phase in humans and other animals.
Researchers from the Okinawa Institute of Science and Technology (OIST) and the University of Washington made observations on the brain activity and skin structure of octopuses, which periodically transition between two states of sleep, “active” and “restful. During active sleep, activity resembling wakefulness was observed, as well as similar to the rapid sleep phase in other animals.
These results raise interesting questions about sleep in animals and its evolution. Previously, only vertebrates were thought to have two-stage sleep, but this study shows that octopuses, which do not have spines, also transition between different stages of sleep. This indicates that the presence of an active sleep stage may be a common feature of complex cognition.
Researchers observed adult octopuses in aquariums for two weeks. During the day, they adopted a “flat resting pose and evenly white skin pattern,” which is a sign of calm octopus sleep. However, about once an hour, the octopus went into an active sleep state, which was accompanied by eye and body movements, as well as rapid breathing.
Electrophysiological recordings of the octopus brain showed that activity during active sleep was similar to that during wakefulness. The strongest activity was observed in the upper parts of the brain, which are associated with learning and memory function.
To confirm that the octopuses were indeed sleeping during active sleep, the researchers tested their responses to physical stimuli. They found that the octopuses needed more stimulation to elicit a response during sleep than during wakefulness.
Interestingly, when bouts of active sleep were interrupted, the next attack came earlier than if the octopuses were napping continuously. This indicates that the active stage of sleep is important for the proper functioning of octopuses.
Scientists speculate that octopuses may improve control of their skin pattern or activate neural activity associated with their experiences while awake. However, the exact mechanism of this phenomenon remains unknown and requires further research.
This study breaks new ground in the understanding of sleep in animals. It emphasizes that sleep is not unique to vertebrates, but may be a common phenomenon in the animal world. Further research may help us better understand the functions of sleep and its evolution.