Sunday, February 10, 2008

Smart Prosthetics, Smart Nerves, Smart Brains

In reference to Learning (Dec 12/ 2007):

Matthias said:
If you look at a genius like Dean Kamen - a great inventor - you will see what I mean.
He is creative and simply doesn't give up.

I watched his 5 minute TED talk and was impressed.

Lately a reader, Kent, sent me this Nov 07 article from BBC news on a parallel development in the UK. It explains how a bionic arm can "feel" - it can't really; there is no way to literally hook a brain up to a device that can be put on and taken off, despite innovations in haptic technology (see here for an old post called Haptic Vest). In this case the amputees "learned" to "feel" their prosthetic arm through sensory nerve transplant from arm to chest wall. They learned to discriminate sensation of their chest skin from that of their "hand".

Fortunately the (very very cool!) original paper by Todd Kuiken et al. is open access. Take a look at the graphics depicting the amazing amount of sensory discrimination the two subjects were able to attain. They relearned their way out of numbness, essentially. The male subject had lost both upper limbs and the female subject had lost her left upper limb. It took awhile, but the sensory nerves to arm/hand transplanted into the chest skin eventually turned back on and their brains rewired for appropriate data collection. Interesting about subcutaneous fat being removed - this moved skin closer to muscle, stimulating the nerves more with underlying muscle movement.


Amputees cannot feel what they touch with their artificial hands, which severely limits usefulness of those hands. We have developed a technique that transfers remaining arm nerves to residual chest muscles after an amputation. This technique allows some sensory nerves from the amputated limb to reinnervate overlying chest skin. When this reinnervated skin is touched, the amputees perceive that they are being touched on their missing limb. We found that touch thresholds of the reinnervated chest skin fall within near-normal ranges, indicating the regeneration of large-fiber afferents. The perceptual identity of the limb and chest was maintained separately even though they shared a common skin surface. A cutaneous expression of proprioception also occurred in one reinnervated individual. Experiments with peltier temperature probes and surface electrical stimulation of the reinnervated skin indicate the regeneration of small diameter temperature and pain afferents. The perception of an amputated limb arising from stimulation of reinnervated chest skin may allow useful sensory feedback from prosthetic devices and provides insight into the mechanisms of neural plasticity and peripheral regeneration in humans.

This is yet another example of how profound neuroplasticity can be, quite apart from how capable the human brain is of incorporating objects into its brain maps (see Place Cells and Grid Cells Part I and Part II).

1 comment:

Kent said...

I knew enough to see that the neural connections for the prothetic arm were unique, but I now understand them much better thanks to your post. The plasticity evinced in this case of neuroplasticity is astounding!