As of right now, I can only find a map of nerve fibers, but not necessarily the individual neuron axons.
For example, here's a map of the nerves in the arm and hand. http://www.innerbody.com/anatomy/nervous/arm-hand
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$\begingroup$ Maybe, sort of; can you clarify why you want this information or what type of map you are looking for? $\endgroup$– Bryan Krause ♦Feb 17, 2017 at 17:51
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3$\begingroup$ Nerves are somewhat variable (the image on your link shows an idealized version). Axons are even more variable than nerves. Consider that nerves are growing out from the CNS to muscles that are developing from a completely different germ layer. The actual axons reaching individual parts of muscles are not at all conserved. $\endgroup$– kmmFeb 17, 2017 at 18:05
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$\begingroup$ @BryanKrause Yes. I'm trying to learn more about how biological neurons could be connected directly to computers instead of indirectly through EEG. If that were possible, I could definitely see full motor and sensory capabilities being implemented in bionic arms. $\endgroup$– ArturFeb 17, 2017 at 19:23
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No it is not possible to map axons at that fine of a scale between individuals.
You mention a possible use for controlling bionic arms. There are a bunch of problems with that approach.
- Like @kmm says, at the fine level there is a ton of variation.
- I think you are failing to appreciate just how many axons there are, even going to a particular muscle; while each muscle fiber only gets input from one axon, there are thousands of fibers in a single muscle.
- The EEG-based approaches to prosthetic control are most relevant when there is a problem with spinal function, for example caused by an injury. In this case, there is no connection between the motor neurons and the brain.
- Axons often degrade if their targets are damaged. Therefore, if a hand is lost in an accident, for example, the neurons projecting to the muscles of the hand will atrophy.
- If the axons themselves are in place, there are already prosthetics that operate based on muscle contractions in existing muscles. It takes some time to train users to use these devices, but most movements you make involve all sorts of muscles you may not realize are involved, and it is quite possible for brain plasticity to allow muscles in, for example, the shoulder, to control a bionic hand after an amputation.
If for some reason the issues I raised don't apply, there is another alternative: mapping. You don't need to know which axons you want information from, you only need to be able to record their activity (which you will need anyways to operate the prosthetic). Record the activity while the patient tries to move their finger, for example: now you know the signal you should transduce into a finger movement. The technical challenge, then, is being able to isolate that signal from all the other signals from all the other axons in the same nerve. This challenge is related to, though not precisely the same as, the challenge of isolating a signal in the EEG.
answered Feb 17, 2017 at 20:10
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$\begingroup$ With diffusion tensor imaging I they're pretty close on mapping fibers, at least in the brain. $\endgroup$– AliceD ♦Feb 17, 2017 at 20:49
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$\begingroup$ @AliceD Source? DTI is worlds away from mapping individual axons, unless some massive new technological leap has totally escaped my notice. It would certainly be possible to use DTI to map the statistical connectivity of different brain regions but that is nothing like what the OP is suggesting. DTI resolution is on the order of mm, axons can be closer to 1 micron. $\endgroup$– Bryan Krause ♦Feb 17, 2017 at 20:53
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1$\begingroup$ aha gotcha. +1 and thanks for clearing that up for me. Perhaps adding your sources may help you get some more up votes. $\endgroup$– AliceD ♦Feb 17, 2017 at 21:50
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$\begingroup$ @AliceD Yes indeed, I'll try to track some down where possible. Possibly of interest to you I did some research on DTI methods and it seems there are some recent works that get the resolution down to 100um and below, but these are with high-strength 7T+ scanners that are sized only for rodents. $\endgroup$– Bryan Krause ♦Feb 17, 2017 at 21:57