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.

Are you a Replicant? Or are you a Repli-CAN?

Oscar Pistorius is the Cyborg of the Moment.



You're probably already aware of his story: a double, below-the-knee amputee as a child, Oz has grown up to be a fantastic runner... with the help of his Ossur brand Cheetah prostheses. For an in-depth introduction, I recommend Wired's article from early last year.

They call him the "Blade Runner." Sexy, no? His Nike ad is pretty hot, too

This week, the International Association of Athletics Federations (IAAF) has ruled that Pistorius's carbon-fiber legs confer an unfair advantage, and has barred him from competing in the Summer Olympics in Beijing. I have yet to read the IAAF report, but news items I've heard have mentioned the "springiness" of the Cheetahs (greater than that of the traditional calf-and-ankle model, but that's not hard to beat) as well as his more horizontal stride - he doesn't waste as much energy bouncing as he runs. I've also heard arguments focusing on his (purported) aerobic efficiency - nonexistent legs don't require oxygen.

These might be valid arguments for an advantage if he consistently beat the intact competition. But he doesn't. His 400 meter best is still a half second short of the Olympic qualifying time. So it's hard to see where the advantage is conferred, exactly.

The day double amputees begin to regularly smoke "able bodied" Olympians, then it may be time to reevaluate whether the competition is fair. Unless and until that happens, I say let him go to the trials. If he qualifies, let him race.

It comes down to energy efficiency. How much effort does an athlete expend to get his or her results? There's no free lunch in the Olympics (or in Major League Baseball either, apparently). But it's unreasonable to suggest that this guy is not working as hard as his counterparts. Insulting, really. Oscar Pistorius isn't a cheater - he's exactly the kind of dedicated competitor who belongs in Beijing this summer.