Totally Unexpected: Scientists Discover: “An Entirely New Way of Thinking in the Nervous System”

Octopuses are not like humans – they are invertebrates with eight arms and are more closely related to clams and snails. Despite this, complex nervous systems develop as many neurons as there are in a dog’s brain to provide them with a wide range of complex behavioral patterns.

This makes them an interesting topic for researchers such as Melina Hale, Ph.D., William Rainey Harper Professor of Organismal Biology and Vice Provost at the University of Chicago, who want to understand how the structures of the nervous system can alternate and perform the same functions. humans, such as feeling the movements of the limbs and controlling the movements.

In a recently published study Current BiologyHala and his colleagues discovered a new and surprising feature of the octopus’s nervous system: a structure that allows the intramuscular nerve cords (INCs), which help the octopus sense arm movement, to connect arms to opposite sides of the animal.

The surprising discovery provides new insights into how invertebrate species independently evolve complex nervous systems. It may also provide inspiration for robotic engineering, such as new autonomous underwater machines.

A horizontal segment at the base of the arm (labeled as A) showing the converging and crossing of the oral INCs (labeled O). Credit: Kuuspalu et al. Current Biology2022

“In my lab, we study mechanosensation and proprioception — how the movements and positions of the limbs are sensed,” Hale said. “Those INCs have long been thought of as being of their own, to help them with an additional goal to answer the kinds of questions that our lab is asking for. So far not much work has been done on them, but past experiments have shown that they are important for arm control.

Thanks to a cephalopod research grant offered by the Marine Biological Laboratory, Hale and his team were able to use young octopuses for study, which were small enough to allow researchers to image the base of all eight arms at once. This team will track INCs through the web to determine their path.

“These polyps were about the size of a nickel or maybe a quarter, so it was a process of placing the specimens in the right orientation and getting the right angle in the section. [for imaging]Adam Kuuspalu, Senior Research Analyst at UChicago and lead author on the study.

Initially, the team studied the major axial nerve cords in the arms, but began to notice that the INCs did not stop at the base of the arm, but instead continued out of the arm and into the animal’s body. Noticing the anatomy of the INCs, they began to trace the nerves, expecting them to form a ring in the body of the polyp, like the axial cords of the nerve.

The imaging team determined, in addition to the length of each arm, that at least two of the four INCs extend into the body of the octopus, where the two adjacent arms pass and merge with the INC of the third arm. The commander means that all arms are equally linked.

He struggled, however, to determine how the system would be maintained in all eight arms. “When we imagine, we realized that not all of them are coming together as we expected, they all seem to be going in different directions, and we were wondering how if the shape of all the weapons was kept, how would it be! work?” said Hale. “I even brought out one of these free toys — a Spirograph — to play around with what it would look like, how it would all fit together in the end. It took a lot of imagining and playing with the pictures as we racked our brains around what was going on before it became clear how it all worked out. let them stick together.

The results were not at all what the researchers expected to find.

“We think this is a new design of the limb-based nervous system,” Hale said. “We haven’t seen anything like this in other animals.”

Researchers don’t yet know what function this anatomical design might serve, but they have some ideas.

“Some of the older papers shared the ways they were perceived,” Hale said. “One study from the 1950s showed that when you manipulate the arm on one side of an octopus with brain damage, you’ll see arms on the other side.” It is therefore possible that these nerves allow for the control of the decentering of the reflexive response or behavior. That said, we also see that the fibers from the nerves go out to everyone through their tracts, so as to allow the continuity of feedback and motor along their length.

The team is now designing experiments to see if they can gain insight into this problem by dissecting the physiology of INCs and their unique distribution. They also study the nervous systems of other cephalopods, squid and cuttlefish, if they share similar anatomy.

Ultimately, Hale believes that in addition to illuminating the unexpected ways invertebrate species can design their nervous systems, understanding these systems can aid in the development of new machine technologies, such as robots.

“Octopus can be a biological inspiration for the design of autonomous undersea devices,” said Hale. “Think of arms – they can bend anywhere, not just at the joints. They can twist, stretch their arms, work with dishes, all independently. The function of an octopus’s arm is much more sophisticated than ours, so understanding how octopuses integrate information and motion sensors can support the development of new technologies.

Report: “Multiple nerve cords connect octopus arms, signaling different ways between arms” by Adam Kuuspalu, Samantha Cody and Melina E. Hale, November 28, 2022; Current Biology.
DOI: 10.1016/j.cub.2022.11.007

The study was based at the United States Naval Research Center.