Targeted reinnervation

A woman’s nerves have been rewired to help her control a prosthetic limb, an experimental procedure for amputees called targeted reinnervation. It’s a fascinating concept, and it works: a noncritical muscle’s nerves are deactivated, and the severed efferent (motor) nerve fibers from the missing limb are inserted into the muscle. The brain can then control a prosthesis by sending motor signals to the muscle. Additionally, the afferent (sensory) nerve fibers from the severed limb are moved to the skin above the same muscle. Stimulation of those nerves are now mapped as sensation originating from the prosthesis. Claudia Mitchell can control her prosthetic arm by sending motor signals to her chest muscle, and experiences cutaneous sensations in her prosthetic arm when the skin on her chest is touched or its temperature is changed.

Of course, rather than simply explaining the news in as clear a way as possible, ABC proceeds to extremes: “Mitchell has become the first real ‘Bionic Woman’: part human, part computer.” She’s first and she’s real, and you can tell because ABC even awarded her the official capitalized title of “Bionic Woman.” Presumptuous, and also inaccurate. In fact, this technology is exciting because it doesn’t have much to do with computers at all. Rather than relying on predictive software to control the motors in the prosthesis (which was the technique used in this BBC producer’s prosthetic foot), Ms. Mitchell controls her hardware directly, with her brain.

In any case, the success of this procedure has led to some interesting discoveries, such as the fact that Ms. Mitchell retains a 1-to-1 mapping of her reinnervated afferent fibers to locations on her prosthesis.

Paul Marasco, a touch specialist and research scientist with the Rehabilitation Institute of Chicago, was brought in to study the hand sensations that Mitchell feels in her chest. He put together a detailed map, connecting what Mitchell’s missing hand feels with the corresponding locations on her chest.

Depending on where you touch her chest, “she has the distinct sense of her joints being bent back in particular ways, and she has feelings of her skin being stretched,” Marasco said.

If a human’s nervous system can be extended to include a prosthesis, it isn’t a stretch to imagine that it can be interfaced with external signal networks, such as other humans’ nervous systems, or the internet. How will this affect embodied cognition? Societal structure? Consciousness?

Here’s a video of Claudia in action. Seems like she’s got style too—the upper part of her artificial arm is covered in a camoflauge pattern. Seen!

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