Scientists discover “an entirely new way to design a nervous system”
Octopuses are not like humans – they are invertebrates with eight arms and are more closely related to clams and snails. Despite this, they have developed complex nervous systems with as many neurons as in a dog’s brain, enabling them to perform a wide variety of complex behaviors.
This makes them an interesting topic for researchers such as Melina Hale, Ph.D., William Rainey Harper Professor of Organmal Biology and Vice Provost at the University of Chicagowho want to understand how alternative structures of the nervous system can perform the same functions as those in humans, such as sensing limb movements and controlling movements.
In a recent study published in Current BiologyHale and her colleagues discovered a novel and surprising feature of the octopus’s nervous system: a structure that allows the intramuscular nerve cords (INCs), which help the octopus sense its arm movements, to connect the arms on either side of the animal. .
The surprising discovery offers new insights into how invertebrate species have evolved complex nervous systems independently. It can also provide inspiration for robotic technology, such as new autonomous underwater devices.
“In my lab, we study mechanosensation and proprioception — how limb movement and positioning are perceived,” Hale said. “These INCs have long been thought to be proprioceptive, so they were an interesting target to help answer the kinds of questions our lab is asking. Not much has been done about it so far, but previous experiments have shown that they are important for arm control.
Thanks to support for cephalopod research from the Marine Biological Laboratory, Hale and her team were able to use juvenile octopuses for the study, which were small enough to allow the researchers to image the bases of all eight arms at once. This allowed the team to trace the INCs through the tissue to determine their path.
“These octopuses were about the size of a penny or maybe a quarter, so it was a process of attaching the specimens in the right direction and getting the right angle when cutting [for imaging]said Adam Kuuspalu, a Senior Research Analyst at UChicago and the study’s lead author.
Initially, the team studied the larger axial nerve cords in the arms, but began to notice that the INCs did not stop at the base of the arm, but rather continued out of the arm and into the animal’s body. Realizing that little work had been done to examine the anatomy of the INCs, they began tracing the nerves, expecting them to form a ring in the octopus’s body, similar to the axial nerve cords.
Through imaging, the team determined that in addition to running the length of each arm, at least two of the four INCs extend into the octopus’s body, where they bypass the two adjacent arms and fuse with the INC of the octopus. third arm. This pattern means that all arms are connected symmetrically.
However, determining how the pattern would hold up in all eight arms was a challenge. “As we were imaging, we realized that they didn’t all come together as we expected, they all seemed to go in different directions, and we were trying to figure out how if the pattern applied to all arms, how would that then can?” work?” said Hale. “I even got out one of those kids’ toys—a spirograph—to play with how it would look, how it would all connect in the end. It took a lot of imaging and playing with drawings, as we got our racked their brains over what might be going on before it became clear how it all fits together.
The results were not at all what the researchers expected to find.
“We think this is a new design for a limb-based nervous system,” Hale said. “We haven’t seen anything like this in other animals.”
The researchers don’t yet know what function this anatomical design might serve, but they have some ideas.
“Some older papers have shared some interesting insights,” Hale said. “A study from the 1950s showed that if you manipulate an arm on one side of the octopus with damaged brain areas, you will see the arms on the other side react. Thus, these nerves may allow decentralized control of a reflexive response or behavior. That said, we also see that fibers go from the nerve cords to the muscles along their lengths, so they may also provide a continuity of proprioceptive feedback and motor control across their lengths.
The team is currently conducting experiments to see if they can gain insight into this question by dissecting the physiology of the INCs and their unique layout. They also study the nervous systems of other cephalopods, including cuttlefish and squid, to see if they share the same anatomy.
Ultimately, Hale believes that understanding these systems not only provides insight into the unexpected ways that an invertebrate species can design a nervous system, but also aids in the development of new engineering technologies, such as robots.
“Octopuses could be a biological source of inspiration for the design of autonomous submarine devices,” says Hale. “Think of their arms — they can bend anywhere, not just at joints. They can twist, extend their arms and operate their suction cups, all independently. The function of an octopus’s arm is much more advanced than ours, so understanding how octopuses use sensorimotor information and integrating motion control can support the development of new technologies.”
Reference: “Multiple nerve cords connect the arms of octopuses, providing alternate pathways for signaling between the arms” By Adam Kuuspalu, Samantha Cody, and Melina E. Hale, November 28, 2022, Current Biology.
The study was funded by the US Office of Naval Research.
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