A new Hebrew University study recently examined the possibility that octopuses, known to be among the most intelligent of invertebrates, could have multiple brains.
The full intelligence of an octopus is not fully understood, however it is known that they have the largest nervous system among invertebrates – even larger than some vertebrates – with more nerve cells not in the brain itself but rather in its body and the tentacles.
The question of multiple brains is one that many researchers are still investigating.
The collection of sensory information and the ability to process it, learn from it and respond accordingly, is an essential aspect of animal behavior. Octopuses, which are considered the most intelligent of the invertebrates even though the exact nature of their intelligence is still unclear, provide us with a unique system for studying the relationship between sensory information, neural processing and motor activity.
Evidence has been presented in the past that each of the octopus's tentacles sometimes functions independently without exchanging information between themselves and the central brain system. There have been other documented cases of only one factor in the body correlating the activity in the tentacles. In any case, in each of the tentacles there are hundreds of suckers, each of which independently has thousands of sensory cells responsible for taste and touch, which can be likened to tentacles with hundreds of tongues.
In the brain of humans and vertebrates there exists an area for each body part, and the greater the amount of sensory cells in a particular organ (such as the tongue or finger), the larger the area of the brain that represents it. Body mapping such as this has not yet been found in the brain of an octopus.
MANY STUDIES in recent years, led by Hebrew University Prof. Benny Hochner, support the idea that during evolution, octopuses have adapted to the "strange structure of their bodies and the unique organization of their nervous system to allow themselves to function efficiently in the absence of the body mapping in the central nervous system.
"It's important to understand that unlike with our body, where the number of joints is relatively limited, the mapping of a flexible body such as that of an octopus – which can be imagined as consisting of infinite joints – would require an unrealistic nervous system of size and complexity.
"In other words, the 'embodied organization' of the complex match between the octopus's body and the brain is what underlies the octopus's adaptation to its environment," Hochner explained.
A new study conducted by Hochner, Dr. Michael Juba and Dr. Tamar Gutnik from the department of Neurobiology at the Institute of Life Sciences at the Hebrew University, in collaboration with Letizia Zulu from Italy's Center for Biorobotics at the Italian Institute for Technology, was published in the scientific journal Current Biology. The learning ability of the octopus was tested and the level of information from the tentacles was examined.
The researchers built two Y-shaped tubes inside the octopus aquariums, with food placed into one end of the Y-branch. The tubes were intentionally built narrow enough so that only one octopus tentacle could fit inside to figure out the location of the food.
The octopuses could not see the arm or the food inside the maze, but learned that in order to obtain the food they had to put an arm into the maze and rely solely on sensory information from the arm moving in the "maze."
THE STUDY focused on two senses.
The first is proprioception, or self-sensation of the body, i.e. the ability to "know" where the arm is or what it does even when it is not seen. This was tested through the octopus's inability to see their tentacles inside the maze. In humans, a major part of this sense relies on sensory cells between the skeletal muscles and joints, which of course are not found in octopuses.
Throughout the experiment the octopus learned to put an arm in the maze and consistently send it to the right end of the y-branch in the tube.
The second sense examined was the sense of touch.
In the experiment the octopuses learned that there is both a smooth and a rough side in the maze, only one of which contains food.
Researches noticed that the octopus in the experiment learned to insert its arm into the tube, feel around, and decide if its arm was in the correct tube to reach the food.
"It is worth noting that in this case, the octopuses eventually opted for slower search movements, which included exploring the interior of the maze," Gutnick explained. "The results of the learning speed are not significantly different from those found in previous studies."
The results of the study prove for the first time that the octopus brain does receive sensory information from the tentacles and that from this information the octopus can draw conclusions about the position and movement of the tentacles.
The study also shows for the first time that the brain can control arm movement in real time even without the sense of sight, meaning that there is an exchange of sensory information from the arm to the brain at a high enough speed to make a decision about continued movement.
In addition, one of the important findings found in the study is that octopuses do not always use the same arm, meaning information learned with one arm is available for use by another arm. From this it can be concluded that the information itself is not processed or stored at the arm level but in the central brain.
"Our study makes it clear that although octopus tentacles have many autonomous movement and sense abilities, they are still an integral part of the octopus's ability as an organism to understand and act in its environment – and when necessary they are under the control of the central nervous system," Gutnik explained. "In addition, the study shows us that this is not an animal with nine brains, but an animal with one large brain and eight smart tentacles."