The most unusual on Earth: scientists have just unveiled the secrets of octopus nervous systems (video).

Octopuses may appear almost like alien creatures, but their remarkable ability to control each of their eight arms fascinates and intrigues scientists. It is known that this control is at least partially due to the segmentation of the nervous system that governs them, yet researchers still did not understand how it works. Now, the mystery of octopuses has been unveiled, reports Science Alert.

In a new study, scientists from the University of Chicago revealed a peculiar way in which cephalopods navigate the world. The researchers believe that their findings could provide insights for future soft robotics projects.

According to co-author of the study, neurobiologist Clifton Ragsdale, if humans manage to decipher the secret of the octopus nervous system that controls such dynamic movements, it could offer valuable clues on how to optimize it. Scientists suggest that this astonishing feature has specifically evolved in soft-bodied cephalopods with suckers to facilitate dynamic movements.

It is no secret that the octopus nervous system is one of the most unusual on Earth. Unlike other intelligent animals, it is highly distributed, with a significant portion of its 500 million neurons spread across all eight limbs. In simple terms, most of the neurons in the cephalopod mollusk are located in its limbs rather than in its head.

Interestingly, individual arms of the octopus are essentially capable of making decisions independently from one another and can even respond to stimuli after being severed. Researchers found that any of the hundreds of suckers can "taste" the chemistry of the environment and change their shape.

Neurons in the octopus's limbs are concentrated along the axial nerve cord, which waves along its length, with nerve nodes concentrated around each sucker. This system appears complex and directed, prompting a team led by neurobiologist Cassidy Olsen to study how exactly the octopus nervous system functions.

During the study, scientists examined longitudinal slices of the arm of the California two-spot octopus (Octopus bimaculoides) under a microscope and discovered something never seen before. Along the axial nerve cord, neuronal cells are packed into segments separated by gaps called septa, rich in connective tissue, where nerves and veins emerge to connect with nearby muscles.

Next, the researchers traced these connections and found that nerves from several segments connect to different muscle areas. This suggests that the segments work together to control the muscles with a high degree of precision. The team also discovered that the nerves for the suckers are interconnected through partitions, creating something akin to a spatial nerve map of the suckers. This enables scientists to achieve fine individual control over each sucker, which octopuses use to perceive their environment through touch and taste.

In the next phase, the scientists focused on identifying the relationship between the segmentation of the axial nerve cord and its function. To do this, they looked at a similar architecture in another group of cephalopods—the squids. It is known that squids diverged from octopuses about 270 million years ago, and thus their limb arrangement is somewhat different: squids also have 8 arms with suckers but possess two tentacles without suckers along the stem, located at the end of a bulb.

Squids and octopuses are known to use their limbs quite differently: octopuses employ their limbs for movement along the sea floor and manipulation of objects, while squids use theirs for capturing and holding prey.

Researchers found that the architecture of the axial nerve cord in the longfin inshore squid (Doryteuthis pealeii) differs significantly from that of octopuses. Furthermore, there was no segmentation in the stems of the suckerless tentacles, but segmentation of the nerves was found in the sucker-bearing bulbs.

Now, scientists believe that the segmented nervous system is linked to the control of the sucker-bearing limbs and is crucial for fine and agile manipulation. Meanwhile, squids likely do not require as many segments since they do not use their suckers for exploring their environment.