The Body Electric

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The Freehand is not for everyone, though. To benefit from the device, patients must have use of a shoulder and upper arm and partial use of their hands. The technology can be fragile, too, and patients must be constantly on guard against infection around the implanted electronics. Another drawback is that the Freehand system provides no tactile feedback for things like temperature, so users also have to be careful when handling hot objects such as cigarettes or coffee. To get around this problem, Thomas Sinkjaer and colleagues at the Center for Sensory-Motor Interaction at Denmark's Aalborg University are developing neural prosthetics that can actually feel the texture of objects and transmit this information back to the user.

"We want to make patients aware of the parts of their bodies that they cannot sense," says Sinkjaer, who has worked with Brian Holgersen for the past six years, "and use sensory information from the skin to control the hand automatically as in able-bodied subjects." This kind of sensitive prosthetic would recruit afferent nerves to send tactile information from paralyzed limbs to other parts of the body, where the sensations could be perceived. With such a device Holgersen might feel the weight of a freshly brewed cup of coffee as a tingling sensation on his cheek; the heavier the cup, the more intense the tingle.

Making this kind of tactile feedback work will be difficult. Hundreds, perhaps thousands, of different nerves would need to be stimulated to create convincing sensations. This is a daunting task, since the hand has the highest density of nerve receptors in the entire body, about 20,000.

Another facet of the bionic future is taking shape in a second-floor laboratory at the University of Louvain in Brussels. There Marie, a 63-year-old Belgian woman, is treated to visions of red, blue and yellow dots arranged in neat little rows like the tops of Lego building blocks. Glimpses of Lego bricks are hardly worth getting excited about, but Marie is enthralled — because she's blind.

Marie (not this woman's real name; she wishes to remain anonymous) can see again thanks to an electrode implanted around her right optic nerve. The electrode is connected to a stimulator installed in a small depression carved from the inside of her skull. A video camera, worn on a cap, transmits images in the form of radio signals to the stimulator, which converts these signals into electrical impulses and sends them along Marie's optic nerve. The optic nerve ferries the signals to Marie's visual cortex, where they are reassembled into an image: in this case, a collection of red, blue and yellow Lego bricks. "The device is an integral part of my body," Marie says. "I don't feel it. I completely ignore it." Marie is one of only about a dozen people in the world who have had visual implants that could potentially restore their sight.

Marie started to lose her vision when a condition known as retinitis pigmentosa caused the rod and cone cells in her retina to degenerate. When rod and cone cells die off, the retina is rendered insensitive to light and the result is blindness. Marie's case followed the typical pattern. First her rod cells went, leaving only a slim tunnel of vision through which she could still manage to recognize objects and read with difficulty. But then as her cone cells failed, this last narrow window on the world snapped shut and she was left completely blind — even though her retina retained a healthy connection to the visual centers of her brain through a functioning optic nerve. Marie's implant splices into the live line of the optic nerve to enable her to see again.

Marie's artificial visual system is called the Microsystem-based Visual Prosthesis (MIVIP) and was designed by Claude Veraart and collaborators at the University of Louvain. The MIVIP consists of a cuff electrode implanted around Marie's right optic nerve. The electrode wraps around the optic nerve like the little plastic sheath on the end of a shoelace. It is connected to a thin cable that snakes its way from the optic nerve exiting the back of Marie's eye and weaves around the outside of her brain to the stimulator implanted in a small cavity in her cranium. The stimulator, which bypasses the damaged rod and cones cells to send electrical signals directly to the optic nerve, is operated by means of radio signals transmitted from the external video camera.

These devices are permanently implanted inside Marie's skull, but to use them she must travel to a small room at the University of Louvain and don what looks like a badly damaged 1960s bathing cap. The cap is made of plastic and has a standard video camera affixed to its front. To use the MIVIP, Marie sits in front of a large white screen on which an alphabet of about 50 different line configurations is projected.