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

Octopuses are not like people – 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 the brains of dogs, which has allowed them to display a wide range of complex behaviors.

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

In a recent study published in Current BiologySo Hill and his colleagues discovered a surprising new feature of the octopus’ nervous system: a structure that allows neuromuscular cords (INCs), which help the octopus sense arm movement, to connect with the arms on either side of the animal.

The startling discovery provides new insights into how invertebrate species evolved independently of complex, neurotic species. It could also provide inspiration for robotic engineering, such as new autonomous underwater devices.

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

Thanks to cephalopod research support provided by the Marine Biology Laboratory, Hill and his team were able to use baby octopuses for the study, which were small enough to allow the researchers to visualize the base of the eight arms at once. This allows the team to track the INCs through the tissue to determine their trajectory.

“These octopuses were the size of a nickel or maybe a quarter, so it was a process of gluing the specimens in the right direction and getting the right angle while cutting. [for imaging]said Adam Kospalo, senior research analyst at UChicago and lead author of the study.

Initially, the team was studying the larger axonal nerve cords in the arms, but they began to realize that the INCs did not stop at the base of the arm, but continued down the arm into the animal’s body. Realizing that little work had been done exploring the anatomy of INCs, they began tracing nerves, hoping that they would form a loop in the octopus’ body, 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’ body, where they bypass adjacent arms and fuse with the INC of the third arm. This pattern means that all arms are connected symmetrically.

However, it was difficult to say how the pattern would hold across all eight arms. “As we were filming, we noticed that they weren’t all as symmetrical as we had hoped, they all seemed to be going in different directions, and we were trying to figure out how, if the pattern is consistent across all the arms, how does this work? To work?” Hill said. “I even brought one of these kids’ toys—the Spirograph—to play with what it would look like and how it would all connect in the end. It took a lot of filming and playing with the graphics as we racked our brains over what might happen before it became clear how it all fit together.” 🇧🇷

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

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

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

“Some of the older papers shared 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 see the arms responding on the other side. Therefore, these nerves may allow decentralized control of reflexive response or behaviour. However, we also see that fibers extend from nerve cords to muscles along their tracts, so they may also allow allergic reactions and motor control along their lengths. 🇧🇷

The team is currently conducting experiments to see if they can gain insight into this question by looking at the unique physiology and mapping of INCs. They are also studying the nervous system of other cephalopods, including cuttlefish and cuttlefish, 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 serve as a biological inspiration for the design of autonomous devices in the deep sea,” Hill said. “Think of your arms — they can bend anywhere, not just at the joints. They can twist and extend their arms and operate suction cups, all independently. The function of an octopus’s arm is much more complex than ours, so understanding how octopuses integrate sensory information and control their Its movement can support the development of new technologies.”

Reference: “Multiple nerve cords connect the arms of the octopus, providing alternative signaling pathways between the arms” By Adam Kospalo, Samantha Cody, and Melina E. Hill, 28 Nov. 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.