I am not a biological scientist and have low biology knowledges in general, but I want to know some thing.

Most of us probably can't even imagine what it feels the sixth finger to be touched. Because we do not have one. We can't imagine what should we do to move the sixth finger, although we can imagine same for the finger we have.

I can assume, that people with anomaly additional part of body, like finger or even hand, can fully control and feel it, independently and separately from the "trivial" one.


Now, let's consider another world for a while. You probably know about USB - it is a protocol for data communication. There can be USB-device with any type of functionality, and USB-port, situated at some another device (PC, for example), where USB-device could be plugged in.

Number of USB ports of some device, where USB-devices could be plugged in (PC, for example) is finite, so if a user already used them, another device can't be used, without changing some PC internals.

But, USB protocol provides a concept of the USB-hub: this is a device, that concentrates multiple usb-devices, it has several USB-ports in the output, that can be used.

So, with such device, user can use even single built-in USB-port with multiple devices. So, although internally, PC provides only one port, the technology itself can provide many devices, without changing internals of host device (PC).

Back to biology

I was thinking: the person, that is born with additional part of body, that completely functionates, can be felt, can be controlled, and the mainly - separately and independently from others, during ontogenesis obtained some "internal", "core" changes somewhere in the brain, or it is just peripheral stuff, i.e. brain provides some analogy of hub functionality?

If second statement is true, that should mean two interesting things:

  1. Theoretically, even for a person born, with 5 fingers we can emulate feelings of the six's finger.
  2. Again, theoretically there can be infinite, or at least pretty big number of degrees of freedom for such feelings.
  • $\begingroup$ This is a site in which we attempt to provide objective answers to biological problems faced by our constituency — students and professionals in biology. Your question fails on all criteria. The 100 reputation granted to members of one SE site when posting to another is based on the assumption they are familiar with conduct on SE sites and will respect sites outside their many area of interest. Please do this. $\endgroup$
    – David
    Commented Nov 6, 2023 at 18:43
  • $\begingroup$ @David, as You write, that my question fails all criteria, I can argue that: 1) why can't I be considered as biology researcher? 2) Why there could not be given objective answer to the question? $\endgroup$ Commented Nov 6, 2023 at 18:53
  • $\begingroup$ @David, 1. Prove that please. Provide the definition of what researcher means, and prove that I do not satisfy the criteria of definition. 2. Because it is not a question - You are wrong from the start. It is question, and it is a question objectively. What does objectivity means? Objectivity - that, which doesn't depends on opinion, on interaction. So, what I wrote is objectively a question, since it satisfies a definition of what question sentence is, and not satisfies what declarative sentence is. What You wrote next is subjectively, since it depends on Your opinion. $\endgroup$ Commented Nov 7, 2023 at 7:27
  • $\begingroup$ I quote "I am not a biological scientist and have low biology knowledges in general". $\endgroup$
    – David
    Commented Nov 7, 2023 at 11:01
  • 1
    $\begingroup$ @David, okay, so we ended up with Your complaints about objectivity and reasearcher. Now You have next. I have read the link You provided, and some further included links. Please quote exact statement that I violated by adding this post, so I could argue, or agree with that. $\endgroup$ Commented Nov 8, 2023 at 7:34

1 Answer 1


I think you'd benefit from reading about the concept of "critical periods" - basically, at different times during development, the brain is learning specific tasks, associating sensory stimuli and motor actions and more complex things, as well (like comprehending and producing language). Some of these things are best studied in model organisms where we can take it apart, but you can also watch a lot of this development in human infants since they are born so early relative to their developmental progress. A newborn really has no voluntary muscle control in their limbs and trunk at all. Arms and legs flail wildly, and only over time do their brains learn and refine how to control those limbs.

I would drop the USB analogy entirely, I don't think it's helping you at all in this case.

Experimentally, it's a bit of a challenge to just "add on" new limbs; it's not like you can tape a new digit on a hand because the developmental processes that connect the nervous system to a digit happen while that digit is growing. The nervous system connections are being made at the same time that the limb or digit is growing. However, there has been study of what happens when you take something away: taping digits together, for example, creates a unified representation in the brain. Occluding one eye causes the brain to use the remaining eye for the entire visual cortex. Some of these experiments are described in this Wikipedia article. These experiments tell us something about the relationship between the brain and the rest of the body: brain regions are dedicated to the parts of the body that sensory stimuli and motor connections are available from. They do not have a pre-ordained accounting of exactly how many or where those sources of information are at, when you take away things that are normally present, brain regions are proportionally dedicated to whatever inputs and outputs are available.

Conceptually, rather than thinking about extra parts, all of your same questions apply just as much to what is "normal". There is no evidence that brain development has any assumption built in that there will be 4 limbs or 5 digits on a hand, rather, connections are made with the nervous system as the limbs and digits develop, and these connections carry information between the CNS and sensory neurons and motor neurons, and the brain develops in response to those connections.

  • $\begingroup$ I got the third paragraph of the answer, but in the first one, it seems there is some misunderstanding from You, or from me. It seems to me, like You appeal to concept\part of brain not like some deterministic biological machine, but rather to a "personality", something, that learns after being born (sorry, I probably expressed what I wanted to write badly). I meant, as well as You wrote next, that fingers, skin surface on them, anyway (as I understand) at the time baby is born (comes out from mother normally) already are connected to the brain. $\endgroup$ Commented Nov 6, 2023 at 19:06
  • $\begingroup$ Probably we can consider a spine as USB-hub, but I asked rather about something more internal, i.e. brain: where all of the "connections" from body comes from to the brain - is there are kinda like sockets, and all "connections" from different parts of body have dedicated socket for, so they all connected separately, or there is one interface in the brain, where all connections come to, sending data maybe on a queue, or maybe all it ones generate some superposition data signal and brain decodes and selects from it many different "packets"? $\endgroup$ Commented Nov 6, 2023 at 19:14
  • $\begingroup$ And the third thing - I did not consider any specific part of the living, i.e. when the brain (human) is developing, not being born yet, or already being born, but rather when a baby is already born and grown. $\endgroup$ Commented Nov 6, 2023 at 19:19
  • $\begingroup$ @Stdugnd4ikbd I don't know what you mean by "personality", but the way we use the word "personality" in neuroscience and psychology it does not mean "learned after being born". Lots of things that are not personality, including motor control, are learned after being born, but a lot of learning happens before birth, too. "Learning" in a biological sense is all of the "software" that the CNS operates on; it is all learned. $\endgroup$
    – Bryan Krause
    Commented Nov 6, 2023 at 19:22
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    $\begingroup$ @Stdugnd4ikbd I think you are taking the computer/brain analogy way too far (this is very common, you're not the only one to do it). You will be much better off starting from scratch, reading about brain development and biology, rather than taking everything you know about how a computer works and trying to find the biological equivalent. There's so much different in the architecture that it just won't help beyond an extremely abstract level. $\endgroup$
    – Bryan Krause
    Commented Nov 6, 2023 at 19:23

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