Thread by @ICoyleGilchrist

Behold my 3D printed model of the octopus nervous system! Huge thanks to @TheMicromuseums who designed it. Here’s a 🧵

The octopus brain has a hole in the middle where the oesophagus runs through

Bee brains have a similar arrangement. Here’s a 3D bee brain that @Insect_Sciences sent me a while ago. Notice both have two large bulges on the sides, they’re the optic lobes where most visual processing happens

Vertebrates have optic lobes too. This is a model of a frog brain. The blue spheres are the optic lobes, the bit in yellow is the cerebrum. In humans the cerebrum is massive and makes up most of the brain

The equivalent of the optic lobe is humans isn’t the occipital lobe (outlined in blue), part of the cerebrum which receives signals from the eyes and does most visual processing, but the superior colliculus (in green) a tiny little lump at the back of the brainstem

Our closest common ancestor with octopuses was about 700m years ago, a rather disappointing worm without a proper brain or eyes. Yet we’ve both evolved them independently.

And yet despite being separated by 700m years of evolution both octopuses and humans can get high together

Researchers found that ecstasy (MDMA) has psychoactive effects on octopuses amp.theguardian.com/science/2018/s…

Other researchers have also ketamine can affect octopuses. Ketamine blocks NMDA receptors in humans. Anti NMDA receptor antibodies cause psychosis and brain inflammation (as seen in ‘brain on fire’ a film about @scahalan experience of limbic encephalitis

The fact that manipulating one tiny receptor can have similar complex effects in the brains of two very different species, which evolved independently of each other, blows my mind. The evolution of the eye in humans and octopuses is another example of parallel evolution

But the octopus eye is really quite different. Unlike humans light hits photo receptors in the octopus eye first and neural signals pass behind the receptors (which seems a much more sensible arrangement) so octopuses don’t have a bind spot

Also octopus eyes only have receptors for black and white. They don’t have cones in their eyes so they shouldn’t be able to see colour, and yet they can do this:

No one knows how (if) an octopus can see the colours around it but theories are that the shape of pupil (a ‘W’) allows them to see colour through a process called chromatic aberration or they ‘see’ through photo receptors in their skin

carnegiemnh.org/octopus-myster…

2/3rd of the neurons in an octopus are outside its brain, each leg (not tentacle because it has suckers all the way along) has its own complex mini nervous system and can act almost independently of the rest of the octopus. Some people think this means they have nine brains

But really it’s more like one central brain and 8 very clever spinal cords.

Vertebrates (like us and rabbits) also do a lot of neural processing outside of our brains -this rabbit has a genetic defect so interneurons in its spine don’t work properly -look what happens when it tries to run

The octopus nervous system is a really good example of a decentralised nervous system. While humans are more centralised it’s worth remembering while we have about 86bn neurons in our brains, we also have 200m neurons in our spine and possibly as many as 600m controlling our gut

But size isn’t everything. Crow brains have up to 1.5bn neurons but they can solve complex tasks, make and use tools, recognise and remember faces for years

Bee brains may only have about a million neurons, but remember they are very highly social. A bee colony might have 80,000 individuals giving a #hivemind of 80bn neurons, nearly the same as a human.

If you’re interested in octopus brains and behaviour @pgodfreysmith’s book Other Minds is definitely worth a read. Or, if you’re a complete geek, read this: