5 ms·

I can imagine that arms equipped with significant neural processing would allow higher-level signals to be sent from the central brain. Rather than in most anim

I can imagine that arms equipped with significant neural processing would allow higher-level signals to be sent from the central brain. Rather than in most animals like ourselves, where the motor cortex basically tells which muscles to contract, the arms might be given a signal to feel around and lift a rock, or just explore and report back. Basically, leaving some or all of the planning to the brain, but offloading control. That, plus tightening the feedback loop between sending (touch) and actuation would make for some pretty useful advantages I would guess.

hypertele-Xii 4y ago
Land animals' brains are behind their eyes because seeing is everything. Octopi live underwater. Light diminishes with depth. More data gained from feeling around currents, so brain goes in tentacle.
- Barrin92 4y ago
  the necessity to see explains the position of the eyes but not necessarily of the brain. After all, you'd see just as well if your brain was in your stomach as long as it's connected to your eyes. duration for the signal to travel is one explanation, but not a great one because nerves are fast. (a lot of nerves take weird detours, the visual cortex itself is located at the back of the head). More mundane explanation is heat dissipation. The brain consumes a lot of energy and emits a lot of heat. Would be pretty hard to get rid of it anywhere else.
  - fuckstick 4y ago
    > because nerves are fast No they’re not. If your optic nerve had to travel from your stomach we’re talking a delay of 100s of milliseconds.
    - Barrin92 4y ago
      they definitely are, about 300 mph (so that'd be about 10-20 ms). In fact one of your nerves, the laryngeal nerve enabling you to control your vocal cords wraps from your head around your heart back to your head, even in giraffes! Evolutionary it was apparently just more beneficial to make the thing longer.
      - fuckstick 4y ago
        That should be up to about 300 mph. There is wide variability depending on the structure of the nerve. Even so that maximum is tremendously slow compared to a wire.
      - hypertele-Xii 4y ago
        You're forgetting to account for response latency as well. It's not enough to see danger quickly, you also have to be able to move your body in response. If the brain was in the abdomen, the latency to move your head would be a roundtrip longer.
  - Jensson 4y ago
    I'd bet on it being too hard for evolution to put eyes far away from the brain. The eyes are basically a part of the brain in every species, the optical nerve is so thick and does signal processing midway, I don't think our genes has a concept for dragging more optical nerves around the body or extending it etc. Maybe with some more billion years of evolution our DNA would create more abstractions, like how to generalize optical nerve paths and not just touch/muscle etc, but as we are now it seems like the logic isn't there. Such a thick nerve bundle would need to get added to the spine with everything else, or risk getting pinched and disabled just by moving around, but for now it seems like the spine abstraction doesn't support optical data.
  - andsoitis 4y ago
    > After all, you'd see just as well if your brain was in your stomach as long as it's connected to your eyes. Assuming the brain and stomach both need mutually exclusive physical space, let's swap the two and see what happens. If the stomach is in the head rather than where it is now then it is right by the mouth, so food need to travel less. So it might be a first order solution to optimal spatial layout of the body components. Except, now there isn't enough time for the food to be digested so you have to move the stomach further away...
  - zasdffaa 4y ago
    Latency. Nerves are not fast, but it's irrelevant if they were: if the man-eating giant cat has a the edge, speed becomes relative, yours vs cats, not absolute.
- kkylin 4y ago
  Actually, the visual cortex of mammals is in the back of the head, about as far from the eyes as possible (https://en.wikipedia.org/wiki/Visual_cortex https://en.wikipedia.org/wiki/Visual_cortex), whereas the visual area of octopus are (I think) right next to their eyes. That said, the comparison is not quite that straightforward because our axons are myelinated, which speeds up signals tremendously. Edit: Ok, "as far as possible" is an exaggeration, but they aren't close.
  - hypertele-Xii 4y ago
    The visual cortex has a direct pathway to the retina via the lateral geniculate nuclei. And there are lots of reflexes to fire, before we have time to understand what we're seeing. Like putting your hands in front of your eyes when an object approaches rapidly, long before you recognize what the object is. There needs to be something between the retina and visual cortex to respond to this quickly enough.
- mellavora 4y ago
  > because seeing is everything. especially for animals which orient using scent.
  - Koshkin 4y ago
    Indeed, and dog’s vision is not very good to begin with.

hypertele-Xii 4y ago

Land animals' brains are behind their eyes because seeing is everything. Octopi live underwater. Light diminishes with depth. More data gained from feeling around currents, so brain goes in tentacle.

Barrin92 4y ago
the necessity to see explains the position of the eyes but not necessarily of the brain. After all, you'd see just as well if your brain was in your stomach as long as it's connected to your eyes. duration for the signal to travel is one explanation, but not a great one because nerves are fast. (a lot of nerves take weird detours, the visual cortex itself is located at the back of the head). More mundane explanation is heat dissipation. The brain consumes a lot of energy and emits a lot of heat. Would be pretty hard to get rid of it anywhere else.
- fuckstick 4y ago
  > because nerves are fast No they’re not. If your optic nerve had to travel from your stomach we’re talking a delay of 100s of milliseconds.
  - Barrin92 4y ago
    they definitely are, about 300 mph (so that'd be about 10-20 ms). In fact one of your nerves, the laryngeal nerve enabling you to control your vocal cords wraps from your head around your heart back to your head, even in giraffes! Evolutionary it was apparently just more beneficial to make the thing longer.
    - fuckstick 4y ago
      That should be up to about 300 mph. There is wide variability depending on the structure of the nerve. Even so that maximum is tremendously slow compared to a wire.
    - hypertele-Xii 4y ago
      You're forgetting to account for response latency as well. It's not enough to see danger quickly, you also have to be able to move your body in response. If the brain was in the abdomen, the latency to move your head would be a roundtrip longer.
- Jensson 4y ago
  I'd bet on it being too hard for evolution to put eyes far away from the brain. The eyes are basically a part of the brain in every species, the optical nerve is so thick and does signal processing midway, I don't think our genes has a concept for dragging more optical nerves around the body or extending it etc. Maybe with some more billion years of evolution our DNA would create more abstractions, like how to generalize optical nerve paths and not just touch/muscle etc, but as we are now it seems like the logic isn't there. Such a thick nerve bundle would need to get added to the spine with everything else, or risk getting pinched and disabled just by moving around, but for now it seems like the spine abstraction doesn't support optical data.
- andsoitis 4y ago
  > After all, you'd see just as well if your brain was in your stomach as long as it's connected to your eyes. Assuming the brain and stomach both need mutually exclusive physical space, let's swap the two and see what happens. If the stomach is in the head rather than where it is now then it is right by the mouth, so food need to travel less. So it might be a first order solution to optimal spatial layout of the body components. Except, now there isn't enough time for the food to be digested so you have to move the stomach further away...
- zasdffaa 4y ago
  Latency. Nerves are not fast, but it's irrelevant if they were: if the man-eating giant cat has a the edge, speed becomes relative, yours vs cats, not absolute.
kkylin 4y ago
Actually, the visual cortex of mammals is in the back of the head, about as far from the eyes as possible (https://en.wikipedia.org/wiki/Visual_cortex https://en.wikipedia.org/wiki/Visual_cortex), whereas the visual area of octopus are (I think) right next to their eyes. That said, the comparison is not quite that straightforward because our axons are myelinated, which speeds up signals tremendously. Edit: Ok, "as far as possible" is an exaggeration, but they aren't close.
- hypertele-Xii 4y ago
  The visual cortex has a direct pathway to the retina via the lateral geniculate nuclei. And there are lots of reflexes to fire, before we have time to understand what we're seeing. Like putting your hands in front of your eyes when an object approaches rapidly, long before you recognize what the object is. There needs to be something between the retina and visual cortex to respond to this quickly enough.
mellavora 4y ago
> because seeing is everything. especially for animals which orient using scent.
- Koshkin 4y ago
  Indeed, and dog’s vision is not very good to begin with.