Could the human brain control, say, 20 tentacles?

How much brain plasticity is there in our control of limbs and digits? If say, we replaced a baby’s arms and fingers with 20 robotic tentacles and raised him from birth to use them, would he be able to?

What about people with six fingers (like the Gattaca pianist), extra arms/toes, etc… can they use them effectively?

If the tentacles are designed like an octopus’s, then most certainly.
http://news.nationalgeographic.com/news/2001/09/0907_octoarm.html

Yes.
A human body’s limbs, and by extension it’s digits, end in an average of twenty protuberances. These are controlled, presumably, in part, by the human brain.

Artificial appendages allow variable ranges of motion, but generally all available digits can be manipulated, with practice.

What if it were 20 testicles?

I can’t cite this properly, but there was a story in an old Discover Magazine about an early virtual reality experiment. “We’re all going to be lobsters.” You controlled the main limbs (with pincers) with your hands, and motions of your shoulders and hips made the legs move. It didn’t take long for people to get fairly good at wiggling the arms and legs.

Look at how good game players get at using their thumbs to control all sorts of complex motions.

It would appear that there’s enough brain capacity to do impressive things. Twenty tentacles might be pushing it, however. Could you run a video game and control twenty characters, even at the level of simplified icons?

There are video games where you control hundreds of characters. That’s mostly done by selecting large groups of them at once and giving the whole group the same orders… but then, that’s mostly what a centipede is doing, too.

Cortical homunculus.

Need answer fast?

Sorry if 20 happened to be the magic number of our fingers and toes… I didn’t think about that. Let’s say some more arbitrary number instead, maybe 37? And also, instead of regular bones and joints and muscles, it’d just be a boneless tentacle with almost unlimited freedom of movement – kinda like how I can move my arm in my shoulder joint any which way, but my hips and legs have a very limited range of motion? What if the legs were replaced with tentacles – would the person be able to learn to use them freely, or would he/she be limited to only the standard leg-like motions (lift up, knee out, ankle left, etc.)

As for the centipede question, that’s a really interesting point. I sure as heck can’t focus on 20 characters at a time, but I can probably use all my fingers in various pre-trained combinations when I’m typing on the keyboard or playing a piano. Would an extra finger be as dexterous, or would the brain be limited to ten, with a more or less useless eleventh finger that just sort of dangles there?

If the extra digit is congenital and fully innervated one would expect that as the child’s brain grew up the control pathways would build up in the sensory and motor cortexes.

I know this isn’t quite the same thing, but do people born with six fingers have full control of the extra digit? What about people who are partial conjoined twins–the twin doesn’t develop fully, and there are extra limbs. Can those be controlled? And does this information really tell us anything about the tentacle question?

Exactly this, thank you. I couldn’t figure out how to word this question properly, but you did a better job.

You mean “one would expect” as in that’s normally what happens (in the medical world), or is this just conjecture? (Not to sound snarky; I just honestly don’t know how things like that work.)

I have thought of the question this way: If you gave a dolphin prosthetic arms and hands with five fingers on each hand (and let’s go all the way and give one opposable thumb on each hand), could the dolphin learn to use them?

My speculation is: Not. Without having arms and hands and fingers, I don’t think a dolphin would have the electrical circuitry in place to operate them either – neither in the brain nor any pathways between the brain and the non-existent limbs and digits.

So that’s my guess about the OP’s question too. If you gave somebody a prosthetic limb with more than 5 fingers on the hand, it wouldn’t be possible to use them. UNLESS. . . Unless you also wired up the extra finger(s) to some other existing circuitry that happened to be nearby (like, maybe you could connect an extra finger or two into the wrist circuitry), or maybe if the prosthetic hand included functioning prosthetic nerves that run all the way up the arm into the brain, and was somehow integrated into the motor system there.

There’s also a question: Given some extra limbs or fingers, could the brain grow new nerves and pathways to use them? It’s known that, when part of the brain is damaged, other areas of the brain will learn to take over some of the damaged functions. But I suspect that the brain cannot develop new circuitry to drive a prosthetic limb with extra digits.

Bill Watterson touched on this in one of his Calvin and Hobbes strips. Calvin is admiring a firefly, and trying to imitate it. He pulls down his pants and tries to make his butt glow, but he can’t figure out how to do it. He tells Hobbes, “I don’t even know what muscles to flex.”

Imagine having an extra arm or tentacle on your body somewhere, and you are trying to operate it. No, don’t imagine that you actually have the extra limb – just imagine that you are imagining having that extra limb and you are trying to move the limb that isn’t really there. Can you think of how you would do that?

Neuroplasticity.

Most cases of extra fingers they end up being tiny and vestigial, and are often clipped off at an early age to no ill effect. Either that or it’s a case of a single finger “branching.” But in cases where it is big enough to be functional and has proper innervation and muscle tone, it can be useful. And cats who are naturally polydactyl often have increased dexterity.