An octopus is a soft-bodied animal working eight limbs without delay with no skeleton to lever towards and no single command centre coordinating them. It manages this by pushing most of its mind out into the arms. Roughly 350 million of its 500 million neurons — about 66 percent — sit in the arms themselves, not within the central mind between its eyes.
The mechanism, described on January 15, 2025 in Nature Communications by Cassady Olson, Natalie Grace Schulz and Clifton Ragsdale on the College of Chicago, is a segmented axial nerve cord running down the centre of each arm. Of their paper on neuronal segmentation in cephalopod arms, neuronal cell our bodies are packed into repeating columns divided by gaps known as septa, with nerves and blood vessels exiting via the septa to close by muscle tissues and suckers. Every section handles a slice of the arm. The arm is, in impact, a sequence of repeated processing items wired in sequence, and the animal’s small central mind units high-level intent slightly than micromanaging each twist.
What sits inside an octopus arm
Strip the pores and skin off an octopus arm and you discover no bone, no cartilage, no shell. What you discover is a muscular hydrostat: a construction made solely of muscle, connective tissue and nervous tissue, the place muscle acts towards muscle and incompressible tissue provides the resistance a skeleton would usually present. The human tongue is built on the same principle, as Olson famous to Fashionable Science.
Down the center of that muscular tube runs the axial nerve twine, or ANC. Olson describes it as roughly equal to a spinal twine, with a cell physique area, a neuropil area, and lengthy tracts connecting the arm again to the mind. The twine snakes forwards and backwards because it travels, swelling right into a bulge over each sucker.
The California two-spot octopus (Octopus bimaculoides) the Chicago workforce studied carries a whole bunch of suckers throughout its eight arms. Every sucker can transfer and alter form independently. Every can also be full of sensory receptors, so the arm tastes and smells what it touches — combining, within the lab’s phrasing, a hand with a tongue and a nostril.
The segmented twine discovery
Olson and Schulz discovered the segmentation nearly by chance. They’d been attempting to picture skinny round cross-sections of arms underneath a microscope, however the tissue stored sliding off the slides. They switched to lengthwise strips. In that orientation, underneath mobile markers, the axial nerve twine resolved into one thing nobody had described: neuronal cell our bodies packed into columns forming discrete segments, like a corrugated pipe.
Between the segments sit the septa. Nerves and blood vessels go away the twine via these gaps and fan out to close by muscle blocks and to the suckers. Crucially, nerves from a number of segments attain overlapping muscle areas. That overlap is the wiring diagram for coordination — the segments don’t act as remoted items, they hand motion off to one another alongside the size of the arm.
Olson put the logic plainly within the college’s announcement: for a really lengthy, versatile arm, one of the best ways to arrange a management system “can be to divide it into segments,” with communication between these segments smoothing the motion out.
Why decentralising the mind works
A sign travelling from an octopus’s central mind out to the tip of an arm and again is sluggish in contrast with a sign that by no means has to go away the arm. Placing the circuitry native means the arm can reply to what it touches earlier than the mind has completed eager about it.
Galit Pelled, a professor of mechanical engineering, radiology and neuroscience at Michigan State College, advised Ars Technica that every arm can course of sensory enter, begin a motion and perform complicated behaviour with out direct instruction from the mind — the arms, in her phrasing, have their very own “mini-brains.”
Her group has put numbers on it. In a research printed in February 2025 in Bioelectronic Drugs, carbon electrode arrays implanted within the octopus anterior nerve twine confirmed that the number of spikes in the first 100 milliseconds after stimulation predicted the movement that followed. Machine-learning fashions may inform whether or not a motion occurred in any respect with 88.64 p.c confidence, and whether or not it was a lateral sweep or a grasp with 75.45 p.c confidence.
The behavioural proof is simple to see in aquariums. An octopus will use two arms to carry a shell and pry it open, three extra to stroll throughout substrate, and one other to succeed in right into a crevice — unexpectedly, all doing totally different jobs. The acute demonstration is autopsy: amputated octopus arms will nonetheless transfer on their very own, reaching and greedy, till the native circuits run out of vitality.
The division of labour is just not random. A 2025 discipline research in Scientific Experiences, which scored 3,907 arm actions from 25 wild octopuses throughout six websites within the Caribbean and Spain, discovered that the front arms did the reaching and exploring while the rear arms did the standing and walking. What it didn’t discover was handedness: left and proper arms have been used with nearly equal frequency, and the arms appeared to work in coordinated pairs slightly than displaying a person favorite.
That’s nonetheless a distinct idea of a physique than a vertebrate carries round. A human mind owns the arms. An octopus mind, extra precisely, negotiates with the arms.
A map of each sucker
Probably the most hanging sample the Chicago workforce discovered is spatial. Nerves for the suckers additionally go away via the septa, connecting systematically to the outer rim of every sucker, which units up a topographic map of sucker place contained in the arm’s personal nervous system. The researchers named it the suckerotopy.
Vertebrates have topographic maps too, within the mind — the well-known cortical homunculus, the place the hand and lips take up outsized actual property as a result of they’re densely innervated. The octopus builds its equal within the limb. The suckerotopy is what lets the animal know, with out central processing, which sucker simply tasted one thing attention-grabbing, and find out how to bend the native section of arm to carry extra suckers to the identical spot.
The wiring, Olson advised Fashionable Science, is harking back to a hoop attractor — a circuit that behaves like a gyroscope, letting an animal hold observe of orientation. Such circuits have been described in insect brains for navigation. Discovering the resemblance in an octopus arm suggests the identical computational trick has been bent to a really totally different drawback: realizing the place your personal suckers are in three-dimensional area.
Squid tentacles as a pure experiment
To check whether or not segmentation is a common cephalopod resolution or one thing particular to sucker management, Olson additionally dissected longfin inshore squid (Doryteuthis pealeii). Squid have eight sucker-lined arms plus two lengthy feeding tentacles. Every tentacle is a naked stalk with a sucker-covered membership on the finish, shot out ballistically to grab prey.
The end result was a pure management experiment. The axial nerve twine within the naked stalk is just not segmented; the membership on the tip is, in the identical corrugated-pipe sample because the octopus arm. The place there are suckers to regulate, there’s segmentation. The place the appendage solely must launch and retract, there’s not.
Octopuses and squid diverged greater than 270 million years in the past, and the segmented twine exhibits up in each wherever a dexterous, sucker-laden appendage wants governing — although not identically. Squid tentacle golf equipment have fewer segments per sucker, which inserts their ecology: squid hunt visually in open water and use the membership as a grabber, whereas octopuses prowl the seafloor and use the arms as taste-and-touch devices.
Smooth robotics is copying the diagram
The engineering payoff is direct. A smooth arm has successfully infinite levels of freedom, which is the rationale it could slip via a crack or curl round an oddly formed object. It is usually the rationale a central controller struggles to command it: the computational price of fixing the arm’s geometry from one mind grows too quick.
In Could 2026, Emanuela Del Dottore, Barbara Mazzolai and colleagues on the Istituto Italiano di Tecnologia printed a tendon-driven soft arm whose ten silicone suckers each carry their own optical contact sensors in Nature Machine Intelligence. Every sucker fires a neighborhood suction reflex on contact; a better layer collects contact instructions from all ten, works out how the thing is mendacity, and picks a grasp. It cites the Chicago segmentation paper, and it grabbed bottles and synthetic starfish underwater with no digicam and no operator. Olson has mentioned the suckerotopy and segmentation outcomes give designers precisely that circuit framework to repeat — repeated native processing items alongside a smooth limb, speaking to their neighbours, coordinated by intent slightly than micromanaged.
The comparability to spacecraft engineering is nearer than it appears to be like. Pushing decision-making out to subsystems so the central pc solely units targets is a sample area engineers have converged on for many years, from hierarchical onboard autonomy for long-duration underwater autos to collaborative autonomy for uncrewed plane and satellite swarms navigating without ground contact. Evolution bought there first, by a whole bunch of tens of millions of years.
The segmentation is the wiring, although, not the entire animal. An octopus opening a jar, copying one other octopus’s resolution, or recognising a person keeper is doing one thing that pulls the central mind and the arms right into a shared computation, and the small print of that handshake are nonetheless open. As ScienceAlert noted in its coverage of the Chicago work, that is among the many most uncommon nervous techniques on Earth, and far of what makes it unusual is how a decentralised physique nonetheless produces coherent, goal-directed behaviour.
Ragsdale’s framing within the college’s announcement is value maintaining in thoughts: animals with sucker-laden appendages that transfer like worms want the correct of nervous system, and totally different cephalopods have, in his phrases, “provide you with a segmental construction” whose particulars shift with the calls for of the surroundings.
The following time an octopus at an aquarium reaches an arm round a nook and gropes at one thing it can’t see, the motion is just not being pushed from behind the eyes. It’s being pushed by a sequence of small clusters of neurons working down that arm, every dealing with its personal section, every mapping its personal suckers, passing alerts to its neighbours, sending solely a abstract again to the mind — a boneless animal with the equal of a spinal twine in each limb, feeling its method throughout the seafloor with 350 million neurons that by no means wanted permission.
