In a scientific first, researchers have recorded brain activity from living octopuses moving freely and blithely going about their octopus business.
This remarkable feat was accomplished by implanting electrodes into the animals' brains and data loggers under the skin that could record 12 hours of brain activity. What precisely the recordings mean has yet to be decoded, but the research demonstrates a first step in understanding the strange and complicated minds of these magnificent sea beasts.
"If we want to understand how the brain works, octopuses are the perfect animal to study as a comparison to mammals," says octopus researcher Tamar Gutnick of the Okinawa Institute of Science and Technology in Japan and the University of Naples Federico II in Italy.
"They have a large brain, an amazingly unique body, and advanced cognitive abilities that have developed completely differently from those of vertebrates."
Octopuses are highly intelligent and extremely curious animals. Not only that, they're very mobile and, with their eight boneless arms, have manipulation and reach skills that are unrivaled in the animal kingdom.
Therefore, trying to attach anything to an octopus that has full use of its body is a futile endeavor. And if you want to know how an octopus's brain works in normal circumstances, it needs to fully use its body. Non-invasive equipment that sticks to the outside of the body, like an electrode cap, wouldn't work.
"If we tried to attach wires to them, they would immediately rip it off," Gutnick explains, "so we needed a way of getting the equipment completely out of their reach, by placing it under their skin."
The solution involved electrodes and data loggers designed to record the brain activity of free-flying birds. These devices are often protected by a waterproof casing of hard plastic that has a relatively large profile and is, therefore, unsuitable for implantation in octopuses, so the team developed a streamlined casing of plastic tubing.
They selected for their work three octopuses of the species Octopus cyanea, also known as the big blue octopus, a large octopus with a cavity within the mantle – the central part of its body – that could accommodate the data logger.
Researchers implanted the electrodes inside each anesthetized octopus directly into the vertical and median superior frontal lobes. These electrodes were connected to the data loggers tucked into each octopus's mantle.
Each data logger had a battery that allowed continuous recording for 12 hours. Researchers returned the animals to their tanks and allowed them to wake and go about their usual activities, their brain activity under surveillance. Meanwhile, a video camera was set up to record what they were doing so that the researchers could compare the brain activity to the behavior of each octopus.
After the recordings were complete, the researchers euthanized the octopuses and retrieved the data loggers. They identified several long-lasting brain activity patterns, including some similar to those seen in mammals. Other patterns, however, are unlike anything in the scientific literature.
What they mean is a mystery. The patterns could not be linked to any of the behaviors seen in the videos. However, that's not necessarily surprising. The brain regions to which the electrodes were attached are associated with learning and memory, and the octopuses were not required to perform any learning or memory tasks during the experiment.
That could be the focus of future experiments, perhaps on a wider range of subjects and species.
"This is a really pivotal study, but it's just the first step," says zoologist Michael Kuba, formerly of OIST and now at the University of Naples Federico II.
"Octopus are so clever, but right now, we know so little about how their brains work. This technique means we now have the ability to peer into their brain while they are doing specific tasks. That's really exciting and powerful."
The research has been published in Current Biology.