By Matt Wood
Octopus arms move with incredible dexterity, bending, twisting, and curling with nearly infinite degrees of freedom. New research from the University of Chicago revealed that the nervous system circuitry that controls arm movement in octopuses is segmented, giving these extraordinary creatures precise control across all eight arms and hundreds of suckers to explore their environment, grasp objects, and capture prey.
“If you're going to have a nervous system that's controlling such dynamic movement, that's a good way to set it up,” said Clifton Ragsdale, PhD, Professor of Neurobiology at UChicago and senior author of the study. “We think it’s a feature that specifically evolved in soft-bodied cephalopods with suckers to carry out these worm-like movements.”
The study, “Neuronal segmentation in cephalopod arms,” was published January 15, 2025, in Nature Communications.
Octopus arm nervous system
Each octopus arm has a massive nervous system, with more neurons combined across the eight arms than in the animal’s brain. These neurons are concentrated in a large axial nerve cord (ANC), which snakes back and forth as it travels down the arm, every bend forming an enlargement over each sucker.
Cassady Olson, a graduate student in Computational Neuroscience who led the study, wanted to analyze the structure of the ANC and its connections to musculature in the arms of the California two-spot octopus (Octopus bimaculoides), a small species native to the Pacific Ocean off the coast of California. She and her co-author Grace Schulz, a graduate student in Development, Regeneration, and Stem Cell Biology, were trying to look at thin, circular cross-sections of the arms under a microscope, but the samples kept falling off the slides. They tried lengthwise strips of the arms and had better luck, which led to an unexpected discovery.
Using cellular markers and imaging tools to trace the structure and connections from the ANC, they saw that neuronal cell bodies were packed into columns that formed segments, like a corrugated pipe. These segments are separated by gaps called septa, where nerves and blood vessels exit to nearby muscles. Nerves from multiple segments connect to different regions of muscles, suggesting the segments work together to control movement.
“Thinking about this from a modeling perspective, the best way to set up a control system for this very long, flexible arm would be to divide it into segments,” Olson said. “There has to be some sort of communication between the segments, which you can imagine would help smooth out the movements.”