The Luke Arm

This is a thing of beauty:



One way to control an upper limb prosthetic is to make clever use of spared nerves. These can be surgically re-embedded in, say, healthy pectoral muscle. Although the signals sent by the nerves are small indeed, the electrical activity of the muscles is sufficient to control a device such as the Luke Arm. In a sense, the re-enervated muscles act as an amplifier!

I wonder if anyone has considered remapping of the sensory cortex after amputation as a potential means of generating realistic sensation in a person with a prosthetic.

For example, some people who have lost their arm and/or hand experience phantom hand sensations when touched on their face or chest. These phantoms are so refined that the palm, fingers and thumb are somatotopically represented on the skin - you can draw a map of the phantom hand on a person's face and chest (V.S. Ramachandran did).

One reasonable explanation for this effect lies in the somatotopy of sensory cortex. If you look at a sensory homunculus:

You can see the area of the cortex that represents input from the hand and arm is adjacent to the area that represent the face (laterally) and trunk (medially). After a loss of input from the arm, neighboring areas may encroach upon the now-dormant cortical real estate, recruiting neurons to subserve face or trunk sensation that were formerly representing the hand. This theory is supported by lower-limb amputees, who sometimes feel phantom foot sensation coincident with genital stimulation - no foolin'! (Why the patient continues to perceive a missing limb at all is a more subtle question.)

In the video, the individual wearing the Luke Arm has a small motor attached to his side, which receives input from a thumb sensor. The more pressure on his prosthetic thumb, the higher the frequency of vibration in the motor. In this way, he has some feedback and can adjust his grip accordingly.

However, a patient experiences sensation in a phantom hand when touched on the chest, would it be effective to deliver sensation to his reconfigured representation of his hand, so he could perceive it in his prosthetic hand? I know that phantoms fade with time and can even change in shape. But if the interface between the prosthetic and the "phantom map" on the chest is used daily and creates a reasonable representation of the arm and hand, perhaps the phantom would not dwindle to nothing but would remain part of the patient's internal map of his body.