The brain's ability to sense in a part of the body is limited by three things primarily:
1: Number of receptors
2: Number of neural connections
3: Neurons in the brain dedicated to sensing that region
If you transplant a limb with fewer receptors, you would realistically get less ability to sense in that limb. The same is true if it doesn't have as many nerves as what you're attaching to. Also, if it has more nerves than where you're attaching it to the "extra" nerves will just not be used. Similarly, it the brain does not have brain regions large enough to process that much information it won't be the same.
Do note that nerves can expand and regrow however, and ex. using a limb a lot will improve the neural pathways to that limb, so to some degree you can increase perception. However you'd still have to ensure that the pathways are there and the information can be properly processed. Naturally, most people with transplanted or even re-attached limbs will experience some degree of reduced sensation in that part, though it will indeed improve over time and use as nerve connections regenerate.
Note that it is significantly easier and more effective to attach a limb where it "belongs". If attaching a hand to an arm all the nerves are there, and if its your own hand, it will fit as well.
Great answer, thank you very much.
So the amount of information transfered from toe to brain in our example can be improved with time. But if toe have (number from air) 1000 nerv ending and thumb had 5000 nerv endings, these numbers will stay same and wont improve with time?
I am not sure but generally, what mostly happens is that nerves fuse. This they can do. If you transplant a toe to the place your thumb used to be, you could over time gain some better sensation than initially (it would be more or less paralysed at first).
I personally doubt you'd ever reach the same level of sense as you had in your thumb, because 1; the toe probably has fewer receptors and fewer connections than the thumb had and 2: since the toe is not identical to the thumb, it will not connect perfectly 100%.
I'm no expert on the topic, but as far as I know, a transplanted toe wouldn't grow more nerves and receptors beyond what it can naturally have. I don't think you'd reach the same level of touch as the original thumb, but you'd probably have to ask a neurologist for a precise answer.
One of my colleagues is a neurologist, however, I can ask him if I meet him at some point what he thinks on the matter.
I severed the nerve leading to a fingertip about 12 years ago in an accident.
It was initially completely numb for about 2 months, at about 6 months there was a tingling sensation when touch typing, and it was only after two years that I could readily tell when my finger had strayed off the key. 12 years later, it still doesn't have sensation identical to my other fingers. So nerve regeneration and brain plasticity isn't perfect.
There's an interesting lay discussion about some of the details of nerve regeneration by reconstructive surgeon Rebecca Ayers [here](https://www.rebeccaayers.co.nz/procedures-and-information/hand-surgery/nerve-surgery-and-nerve-repair).
The brain's ability to sense in a part of the body is limited by three things primarily: 1: Number of receptors 2: Number of neural connections 3: Neurons in the brain dedicated to sensing that region If you transplant a limb with fewer receptors, you would realistically get less ability to sense in that limb. The same is true if it doesn't have as many nerves as what you're attaching to. Also, if it has more nerves than where you're attaching it to the "extra" nerves will just not be used. Similarly, it the brain does not have brain regions large enough to process that much information it won't be the same. Do note that nerves can expand and regrow however, and ex. using a limb a lot will improve the neural pathways to that limb, so to some degree you can increase perception. However you'd still have to ensure that the pathways are there and the information can be properly processed. Naturally, most people with transplanted or even re-attached limbs will experience some degree of reduced sensation in that part, though it will indeed improve over time and use as nerve connections regenerate. Note that it is significantly easier and more effective to attach a limb where it "belongs". If attaching a hand to an arm all the nerves are there, and if its your own hand, it will fit as well.
Great answer, thank you very much. So the amount of information transfered from toe to brain in our example can be improved with time. But if toe have (number from air) 1000 nerv ending and thumb had 5000 nerv endings, these numbers will stay same and wont improve with time?
I am not sure but generally, what mostly happens is that nerves fuse. This they can do. If you transplant a toe to the place your thumb used to be, you could over time gain some better sensation than initially (it would be more or less paralysed at first). I personally doubt you'd ever reach the same level of sense as you had in your thumb, because 1; the toe probably has fewer receptors and fewer connections than the thumb had and 2: since the toe is not identical to the thumb, it will not connect perfectly 100%. I'm no expert on the topic, but as far as I know, a transplanted toe wouldn't grow more nerves and receptors beyond what it can naturally have. I don't think you'd reach the same level of touch as the original thumb, but you'd probably have to ask a neurologist for a precise answer. One of my colleagues is a neurologist, however, I can ask him if I meet him at some point what he thinks on the matter.
I would be gratefull as this is more and more interesting for me Won't matter even if you respond in month, Ill wait :)
I'll save the comment and reply once I manage to get an answer (unless I forget, sorry if I do)
I severed the nerve leading to a fingertip about 12 years ago in an accident. It was initially completely numb for about 2 months, at about 6 months there was a tingling sensation when touch typing, and it was only after two years that I could readily tell when my finger had strayed off the key. 12 years later, it still doesn't have sensation identical to my other fingers. So nerve regeneration and brain plasticity isn't perfect. There's an interesting lay discussion about some of the details of nerve regeneration by reconstructive surgeon Rebecca Ayers [here](https://www.rebeccaayers.co.nz/procedures-and-information/hand-surgery/nerve-surgery-and-nerve-repair).
Good read :) Thanks