how multi-brained animals function?


A leech (Hirudinea) has 32 brains throughout its segmented body. An Octopus (Octopoda) has 9 brains, one for its head and 8 for its arms (legs?).

How do these animals process tasks using multiple brains? It would suck if 3 out of your 8 arms wanted to go find a place to hide while your brain and other 5 arms are actively hunting.

In: 228

Each “brain” is actually dedicated to some functions. It works just like a computer. For example some software is going to ask for a specific data. It does not care on which memory chip or hard drive that data is stored, it just asks a controller for that data. The controller will check wether the program is allowed to access it, then check which subpart is supposed to have it, then ask the subpart to get it. Then that subpart will locate the data, and maybe it encrypted or compressed it to store more, so it will decrypt and decompress it before sending it back.

The program does not know nor care where the data was, nor if it was encrypted or compressed.

Think of each of these on the chain as “a brain” .

just because theres multiple brains doesnt mean they have multiple personalities or every brain has a goal its trying to accomplish. The brains are still connected and usually theres a “main” brain that gives “orders”, which are processed by the other brains.

Humans do experience a couple of things that are analogous; even as centralized as we are, not all choices our bodies make are routed through the brain. The instinct to jerk your hand away from a burn, or to kick your foot when your knee is tapped, both get the greenlight signal from the spinal cord. Your conscious brain has no control over what you do in the milliseconds between that signal hitting the spinal cord and your brain processing.

It’s hard to say what any animal experiences for certain. Something like a leech almost certainly doesn’t have much higher stream of thoughts separate from its instinct, so may as well localize the neurons. Octopi are more intelligent; most research suggests that they use the neuron clusters in their arms to improve muscle memory and reflexes, rather than independent learning or decision-making which is in the central brain.

Technically, you could kinda say that humans have two brains (left and right), with a very high bandwidth connection between the two. But unless this connection is severed, you don’t “feel” like two entities.

NB: I can’t remember what happens to people whose hemispheres are disconnected, but I remember learning about it some time ago. If you’re curious, there’s definitely something somewhere on the internet.

The fact that there are 9 separate lobes in an octopus does not mean there are 9 separate consciousness. Humans have two lobes which happen to be next to each other. If we evolved to have our lobes further separated, we would think a bit slower in some ways, since it takes time for signals to move across nerves. But we wouldn’t necessarily think in a different way.

Furthermore, there’s a difference between making decisions (which we call executive functions), and figuring out how to perform those decisions. If you decide to take a sip from a cup of water, a relatively small part of the brain is making that decision. A larger part of your brain and nervous system is involved in pulling it off:

Your visual centers are keeping track of the glass and its position relative to you and the floor.

Your sensory centers are processing the feeling of the glass in your hand, the water on your lips, the position of your arms etc

Your motor centers are controlling the movement of your arm, and fine tuning it based on feedback from your visual and sensory centers

And so much more. None of this is conscious. A lot of this doesn’t even happen in our brains, but in our spinal chord. We still have *executive* control over what our bodies are doing, we just automate a lot of the fine detail.

So why have many brains in the arms instead of one centralised brain? Well it depends what you’re optimising for.

If we had tiny brains in our arms, we could have less brain in our heads, and thus smaller heads. This would have many advantages – childbirth in particular would be a lot easier. Our arm-brains would be closer to the muscles they were moving, allowing them to react faster to touch stimulus. But they’d be further from our eyes, so we’d react slower to visual stimulus. We are *very* visual creatures, so that’s probably a big problem.

The brains don’t have their own opinions they are there for specific functions. The octopus tells the brains in the legs it wants to move to x place and the brains limited to controlled movement make it so.
They are not a community of brains having a communal chat

Well, as centralised as our brain is, it has many different compartments that are good for different things and we would function equally well if they were separated into smaller “brains”. In the end, our brain is just a place where the complicated neuronal networks reside, but they don’t have to be necessary concentrated in a ball inside a skull.

Vertebrates (like us) have a special evolutionary trait that lets signals travel through nerves exceptionally fast (called myelin). Non-vertebrates don’t have this, so separating those compartments into different “brains” lets them be closer to the organs they command or take sensory input from and makes their reaction times faster.

You don’t really get to have a single answer for all multi brained creatures.

You see in many ways, octopuses are the closest thing to having aliens on earth. These intriguing cephalopods are incredibly unique, boasting three hearts pumping blue blood. Octopuses possess a central brain. Situated between their eyes, this brain has a distinct doughnut-like shape, forming a ring around the creature’s esophagus. Technically, when an octopus ingests food, it passes through the “center” of this central brain. This is just one of many facts highlighting how different the anatomy of an octopus’s nervous system is compared to vertebrates and many other invertebrates. Neurons are like messengers that send signals and information from the brain to various parts of a creature’s body. Across its entire body, the typical octopus – scientific name Octopus vulgaris – possesses approximately 500 million neurons. That may sound like a lot, but humans have upwards of 100 billion. However, octopuses have roughly the same number of neurons as dogs, known for their ability to learn various commands. Therefore, it’s not much of a stretch to say that octopuses are keenly intelligent – especially for invertebrates.

Approximately 180 million of the 500 million neurons found in an octopus are concentrated in the central brain. Roughly 40 million or so additional neurons are located in each of the ganglia of each of its eight arms, or tentacles. Therefore, 320 million of an octopus’s neurons – more than two-thirds of them – are found at the bases of its arms rather than in its central brain. Incredibly, a single octopus arm possesses more neurons than you will find in a frog’s entire body – just one of many intriguing facts about their nervous systems. Because each arm has its own ganglia, or cluster of neurons, each arm can act independently of an octopus’s central brain and other arms. The neurons at the base of each arm connect to suckers spread across it; typically, each arm has roughly 250 suckers. Each sucker may have around 10,000 neurons, which it uses to detect physical sensations via touch. These neurons also sense chemicals, allowing each arm to smell and taste objects while exploring them. Octopuses lack proprioception. This means that they don’t have a fixed “map” in their minds allowing them to know what various parts of their bodies are doing. While a human can target a spot on their back without physically seeing it, octopuses lack this perception entirely. There’s a good reason for this: Unlike humans, octopuses don’t maintain a static body shape. Instead, their bodies are remarkably fluid, constantly changing to adapt to the environment. Octopuses make up for their lack of proprioception by having those separate “mini-brains” at the base of each of their eight arms.

Oh, and here are cons to having multiple brains for octopus.
They can react faster to threats because individual ganglia don’t have to communicate with the central brain.

They can fine-tune the movement of each arm, passing the work off to the ganglia.

They can regenerate new arms if one is severed – and the new arm even generates a new ganglion.

As for your leech creatures, not exactly, but you can say that. Leech is an annelid, which are catagorized by body segmenta. But unlike other annelids, it’s internal and external segmentation do not correspond each other. Internally it’ body is divided into 32 parts each with its own corresponding brain! They are not actually different but its just the same brain that is segmented. Each segment has its own neuronal ganglia which are connected to the adjacent one. So precisely it does not have 32 brains but a single brain that exists in 32 parts throughout the body (Anatomically). But physiologically because each ganglia control their respective segments,and usually work independently, you can also say that it have 32 brains! (Physiologically).

Humans have an enteric (intestines) nervous system which acts independently from the brain while simaltaneously communicating with the brain. Similarly, the spinal cord controls reflexes before the signals even reach the brain.
In regards to the octopus and leach comparisons, another commenter perfectly summed up how they would use there *polybrain* bodies