Scientists discover ‘completely new way to engineer the nervous system’

Octopuses are not like humans – they are invertebrates with eight arms and closely related to clams and snails. Despite this, they have evolved complex nervous systems with as many neurons as canine brains, which has allowed them to display a wide range of complex behaviours.

This makes it an interesting topic for researchers such as Melina Hill, Ph.D., William Rennie Harper Professor of Biology of Organisms and University Vice Chancellor at University of Chicagowho want to understand how alternative structures of the nervous system can perform the same functions as humans, such as sensing limb movements and controlling locomotion.

In a recent study published in Current BiologyHill and his colleagues discovered a surprising new feature of the octopus’s nervous system: a structure that allows neuromuscular cords (INCs), which help the octopus feel the movement of its arms, to connect the arms on opposite sides of its body. animal.

This surprising discovery provides new insights into how invertebrate species independently develop complex nervous systems. It could also inspire robotic engineering, such as new autonomous underwater devices.

“In my lab, we study mechanosensation and proprioception — how limb movement and location are sensed,” Hill said. “These INC molecules have long been thought to induce sensitization, so they were an interesting target to help answer the kinds of questions our lab was asking. To date, not much work has been done on it, but experimental studies have indicated that it is important for arm control.

Grace au soutien à la recherche sur les céphalopodes offered by the laboratoire de marine biologie, Hale et son équipe ont pu utiliser de jeunes pieuvres for l’étude, qui étaient suffisamment petites pour mettre aux chercheurs d’imager la base des huit bras à la Once. This allowed the team to track the INCs through the tissue to determine their trajectory.

“These octopuses were about the size of a nickel or maybe a quarter, so it was a process to fix the specimens in the right orientation and get the right angle while cutting. [for imaging]said Adam Koospalo, senior research analyst at UChicago and lead author of the study.

Initially, the team studied the larger axonal nerve cords in the arms, but they began to notice that the INCs did not stop at the base of the arm, but rather continued out of the arm into the animal’s body. Realizing that little work had been done to explore the anatomy of INC molecules, they began tracing nerves, expecting them to form a loop in the body of an octopus, similar to axonal nerve cords.

Through imaging, the team determined that in addition to running the length of each arm, at least two of the four cylinders extend into the octopus’s body, as they bypass adjacent arms and fuse with the octopus. This pattern means that all arms are connected symmetrically.

It was difficult, however, to determine how the model would fit into the eight arms. “As we were imagining, we realized they didn’t all come together the way we expected, they all seemed to be going in different directions, and we were trying to figure out how if the pattern is consistent for all the arms, how could it work? Hill said. “I even took out one of these kids’ toys—the Spirograph—to play with what it would look like, and how everything would connect in the end. It took a lot of pictures and playing with the graphics when we got together. Dig our heads into what might be going on before we find out how it all fits together.

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

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

The researchers don’t yet know what this anatomical design was used for, but they do have some ideas.

“Some old newspapers have shared some interesting information,” Hill said. A study from the 1950s showed that when you manipulate an arm on one side of an octopus with damaged brain regions, you will see the arms interact on the other side. Therefore these nerves could allow for decentralized control of reflexive response or behaviour. However, we also see that the fibers exit from the nerve cords into the muscles along their pathways, so they can also allow the continuity of allergic reactions and motor control along their entire length.

The team is currently conducting experiments to see if they can better understand this question by analyzing the physiology of INCs and their unique arrangement. They also study the nervous system of other cephalopods, including cuttlefish and squid, to see if they share similar anatomy.

Ultimately, Hill believes that in addition to shedding light on unexpected ways invertebrate species can engineer the nervous system, understanding these systems could help develop new engineering technologies, such as robotics.

“Octopuses could be a source of biological inspiration for the design of autonomous underwater devices,” Hill said. “Think of their arms — they can bend anywhere, not just at the joints. They can twist and extend their arms and operate their suction cups, all independently. Octopus arm function is much more developed than ours, so understanding how octopuses integrate sensorimotor information and motion control could support the development of new technologies.

Reference: “Multiple nerve cords connect the arms of the octopus, providing alternative pathways for signaling between the arms” By Adam Koospalo, Samantha Cody, and Melina E. Hill, Nov. 28, 2022, Available Here. Current Biology.
DOI: 10.1016/j.cub.2022.11.007

The study was funded by the United States Office of Naval Research.