Scientists Discover “An Entirely New Way of Designing a Nervous System”


Octopus

This groundbreaking discovery offers new insights into the evolution of complex nervous systems in invertebrate species and has the potential to inspire the development of autonomous underwater devices and other robotics engineering innovations.

Octopuses are not like humans – they are invertebrates with eight arms and are more closely related to clams and snails. Despite this, they have evolved complex nervous systems with as many neurons as in the brains of dogs, allowing them to exhibit a wide range of complex behaviors.

This makes them an interesting subject for researchers like Melina Hale, Ph.D., William Rainey Harper Professor of Organismal Biology and Vice Provost at the University of Chicago, who want to understand how alternative nervous system structures can perform the same functions as those in humans, such as sensing limb movement and controlling movement.

In a recent study published in Current Biology, Hale and her colleagues discovered a new and surprising feature of the octopus nervous system: a structure that allows the intramuscular nerve cords (INCs), which help the octopus sense its arm movement, to connect arms on opposite sides of the animal.

The startling discovery provides new insights into how invertebrate species have independently evolved complex nervous systems. It can also provide inspiration for robotic engineering, such as new autonomous underwater devices.

Octopus INCs Cross in the Body of the Animal

A horizontal slice at the base of the arms (labeled as A) showing the oral INCs (labeled as O) converging and crossing. Credit: Kuuspalu et al., Current Biology, 2022

“In my lab, we study mechanosensation and proprioception — how the movement and positioning of limbs are sensed,” said Hale. “These INCs have long been thought to be proprioceptive, so they were an interesting target for helping to answer the kinds of questions our lab is asking. Up until now, there hasn’t been a lot of work done on them, but past experiments had indicated that they’re important for arm control.”

Thanks to the support for cephalopod research offered by the Marine Biological Laboratory, Hale and her team were able to use young octopuses for the study, which were small enough to allow the researchers to image the base of all eight arms at once. This let the team trace the INCs through the tissue to determine their path.

“These octopuses were about the size of a nickel or maybe a quarter, so it was a process to affix the specimens in the right orientation and to get the angle right during the sectioning [for imaging],” said Adam Kuuspalu, a Senior Research Analyst at UChicago and the lead author on the study.

Initially, the team was studying the larger axial nerve cords in the arms but began to notice that the INCs didn’t stop at the base of the arm, but rather continued out of the arm and into the body of the animal. Realizing that little work had been done to explore the anatomy of the INCs, they began to trace the nerves, expecting them to form a ring in the body of the octopus, 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 body of the…



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