Octopuses are considered to be among the most intelligent invertebrates. Their sensory and motor activities are autonomous and coordinated by a complex central nervous system. The octopus’ brain comprises many neurons organized into numerous distinct lobes, the functions of which have been proposed based largely on the results of lesioning experiments.
Because the octopus lacks any hard structure to which recording equipment can be anchored and uses its eight flexible arms to remove any foreign object attached to the outside of its body, in-vivo recording of electrical activity from behaving octopuses has thus far not been possible.
Now, scientists record the first-ever brain waves from freely moving octopuses. Conducted by the Okinawa Institute of Science and Technology (OIST), the study is crucial to understanding how octopus brains control their behavior. It could offer clues to the common principles needed for intelligence and cognition.
Dr. Tamar Gutnick, first author and former postdoctoral researcher in the Physics and Biology Unit at the Okinawa Institute of Science and Technology (OIST), said, “If we want to understand how the brain works, octopuses are the perfect animal to study as a comparison to mammals. They have a large brain, an amazingly unique body, and advanced cognitive abilities that have developed completely differently from those of vertebrates.”
“Octopuses have eight powerful and ultra-flexible arms, which can reach anywhere on their body. If we tried to attach wires to them, they would immediately rip it off, so we needed to get the equipment out of their reach by placing it under their skin.”
Scientists settled on small and lightweight data loggers as the solution, initially designed to track the brain activity of birds during flight. The team modified the devices to be waterproof and compact enough to slip inside the octopuses easily. Up to 12 hours of continuous recording were possible with the batteries, which had to operate in a low-air condition.
Due to its bigger size, the researchers decided to use Octopus cyanea, also called the day octopus, as their model animal. Three octopuses were put to sleep before a logger was inserted into a hole in the mantle’s muscle wall. The most accessible portion of the octopus’s brain, known as the vertical lobe and median superior frontal lobe, is where the scientists implanted the electrodes.
After completion of the surgery, the octopuses were returned to their home tank and monitored by video. After five minutes, the octopuses had recovered and spent the following 12 hours sleeping, eating, and moving around their tank, as their brain activity was recorded. The logger and electrodes were then removed from the octopuses, and the data was synchronized to the video.
The researchers discovered various diverse patterns of brain activity, some of which resembled mammalian patterns in size and shape, while others were sluggish oscillations with very long amplitudes that had never been observed previously.
Dr. Gutnick said, “We are not yet able to link these brain activity patterns to specific behaviors from the videos. However, this is not completely surprising as they didn’t require the animals to do specific learning tasks.”
“This is an area that’s associated with learning and memory, so to explore this circuit, we need to do repetitive memory tasks with the octopuses. That’s something we’re hoping to do very soon!”
According to scientists, this method of recording brain activity from freely moving octopuses can be used in other octopus species. It could help determine several facts, including how octopuses learn, socialize, and control the movement of their body and arms.
Prof. Michael Kuba, who led the project at the OIST Physics and Biology Unit and now continues at the University of Naples Federico II, said, “This is a pivotal study, but it’s just the first step. Octopuses are so clever, but right now, we know so little about how their brains work. This technique means we now can peer into their brain while they are doing specific tasks. That’s exciting and powerful.”