Sleep behavior has been widely studied in vertebrates, such as mammals, birds, and some reptiles. However, know how invertebrate animals sleep It continues to be a great challenge for science due to the technical difficulties posed by their soft bodies, their rigid shells or the aquatic environment, among other reasons.
Until now, it was thought that only the former had two dream states, the rapid eye movement phase (REM, for its acronym in English) and the non-REM phase. Thanks to the work of a group of scientists from Brazil, published in the journal IScience, it has been shown that the octopus species Octopus insularis, typical of the coasts of Brazil, presents two similar sleep states: ‘quiet sleep’ and ‘active sleep ‘.
The alternation of sleep states observed in the octopus insularis seems quite similar to ours, despite the enormous evolutionary distance between cephalopods and vertebrates “
“The alternation of sleep states observed in the octopus insularis seems quite similar to ours, despite the enormous evolutionary distance between cephalopods and vertebrates, with an early divergence of lineages about 500 million years ago”, explains its author. Sylvia Medeiros, from the Brain Institute of the Federal University of Rio Grande do Norte, Brazil.
As explained in the study, the species octopus insularis fulfilled all the criteria to define sleep, since these cephalopods choose a preferred resting place and adopt a typical posture of lowered head, arms wrapped around the body, immobile body except for shrinking sporadic and rapid movement of the suction cups. In addition, they maintain a pale body color, closed eye pupils, and a reduced respiration rate.
Color changes in dreams
To confirm their theory, the team recorded on video to four specimens, introduced in urns, and evaluated their behavior. “We observed periods in which the animals were extremely calm, with uniformly pale skin and with the pupils of the eyes contracted to a slit. Then, at a certain moment –after about 6 minutes–, the animals suddenly began to change color and move both eyes while contracting the suction cups and the body, with many muscular jerks ”, he details to SINC Sidarta Ribeiro, co-author of the study.
Scientists suspect that both states were of sleep because they always occurred in tandem, first quiet sleep and then active sleep, similar to what is observed in vertebrates
“We decided to perform sensory stimulation tests to quantify the threshold of arousal throughout the sleep-wake cycle. The results show that in both sleep states the octopuses needed a strong stimulus to evoke a behavioral response, compared to the alert state, during which the animals are sensitive to very weak stimuli ”, continues the researcher. That is, in those two stages They were a sleep.
In this way, during the active sleep, the animal dynamically changed color, moved its eyes and performed muscle jerks. On the other hand, with the quiet sleep, his color was pale, his eyes were kept closed and he made very smooth and slow movements.
During active sleep, the octopus may experience a state analogous to REM sleep, which is the state during which humans dream the most.
This finding raises the possibility that octopuses experience something similar to Sound. “It is not possible to say that they are dreaming, but our results suggest that during active sleep the octopus could experience a state analogous to REM sleep, which is the state during which humans dream the most,” Medeiros compares.
If so, they are likely to be dreams much less complex than those of humans. “Active octopus sleep has a very short duration, from a few seconds to a minute. If there is a dream during this state, it should be similar to a small video clip or even a gif ”, exemplifies the author.
Likewise, the alternation in mammals between quiet sleep and active sleep favors memory consolidation. “By analogy, in the octopus it can reflect the evolutionary pressure to process a heavy load of newly acquired memories that need to be integrated into distant brain regions ”, he considers.
Being so different and separate species, such as cephalopods and the rest of vertebrates, the following question arises: how could they develop physiological processes in such a similar way?
“The independent evolution in cephalopods of an ‘active sleep’ analogous to REM sleep in vertebrates may reflect an emergent property common to centralized nervous systems that reach a certain complexity,” says Medeiros.
According to this hypothesis, “the similarities between cephalopods and vertebrates are probably a consequence of similar selective pressures, related to the demanding cognitive loads experienced by these separate groups of animals ”, concludes Ribeiro.
Medeiros SLS, et al. “Cyclic alternation of quiet and active sleep states in the octopus.” IScience
Rights: Creative Commons.