Neuroscientist Paul Bach-y-Rita hypothesized in the 1960s that "we see with our brains not our eyes." Now, a new device trades on that thinking and aims to partially restore the experience of vision for the blind and visually impaired by relying on the nerves on the tongue's surface to send light signals to the brain.
Legal blindness is defined by U.S. law as vision that is 20/200 or worse, or has a field of view that is less than 20 degrees in diameter. The condition afflicts more than one million Americans over the age of 40, according to the National Institutes of Health. Adult vision loss costs the country about $51.4 billion per year.
About two million optic nerves are required to transmit visual signals from the retina—the portion of the eye where light information is decoded or translated into nerve pulses—to the brain's primary visual cortex. With BrainPort, the device being developed by neuroscientists at Middleton, Wisc.–based Wicab, Inc. (a company co-founded by the late Back-y-Rita), visual data are collected through a small digital video camera about 1.5 centimeters in diameter that sits in the center of a pair of sunglasses worn by the user. Bypassing the eyes, the data are transmitted to a handheld base unit, which is a little larger than a cell phone. This unit houses such features as zoom control, light settings and shock intensity levels as well as a central processing unit (CPU), which converts the digital signal into electrical pulses—replacing the function of the retina.
From the CPU, the signals are sent to the tongue via a "lollipop," an electrode array about nine square centimeters that sits directly on the tongue. Each electrode corresponds to a set of pixels. White pixels yield a strong electrical pulse, whereas black pixels translate into no signal. Densely packed nerves at the tongue surface receive the incoming electrical signals, which feel a little like Pop Rocks or champagne bubbles to the user.
It remains unclear whether the information is then transferred to the brain's visual cortex, where sight information is normally sent, or to its somatosensory cortex, where touch data from the tongue is interpreted, Wicab neuroscientist Aimee Arnoldussen says. "We don't know with certainty," she adds.
Like learning to ride a bike
In any case, within 15 minutes of using the device, blind people can begin interpreting spatial information via the BrainPort, says William Seiple, research director at the nonprofit vision healthcare and research organization Lighthouse International. The electrodes spatially correlate with the pixels so that if the camera detects light fixtures in the middle of a dark hallway, electrical stimulations will occur along the center of the tongue.
"It becomes a task of learning, no different than learning to ride a bike," Arnoldussen says, adding that the "process is similar to how a baby learns to see. Things may be strange at first, but over time they become familiar."
Seiple works with four patients who train with the BrainPort once a week and notes that his patients have learned how to quickly find doorways and elevator buttons, read letters and numbers, and pick out cups and forks at the dinner table without having to fumble around. "At first, I was amazed at what the device could do," he said. "One guy started to cry when he saw his first letter."
Wicab will submit BrainPort to the U.S. Food and Drug Administration for approval at the end of the month, says Robert Beckman, president and chief executive officer of the company. He notes that the device could be approved for market by the end of 2009 at a cost of about $10,000 per machine.
The challenge of rechecking vision
Wicab is working with the University of Pittsburgh Medical Center's UPMC Eye Center for further testing on BrainPort. Optometrist Amy Nau will test it, along with other artificial devices such as retinal and cortical implant chips, in order to develop criteria for monitoring the progress of artificial sight.
"We can't just throw up an eye chart. We have to take a step back and describe the rudimentary precepts that these people are getting," Nau says. "The images are in black and white, pixilated. How do you recheck vision?"
Nau is particularly interested in the BrainPort because it is non-invasive, unlike implants.
The key to the device may be its utilization of the tongue, which seems to be an ideal organ for sensing electrical current. Saliva there functions as a good conductor, Seiple said. Also it might help that the tongue's nerve fibers are densely packaged and that these fibers are closer to the tongue's surface relative to other touch organs. (The surfaces of fingers, for example, are covered with a layer of dead cells called stratum corneum.)
"Many people who have acquired blindness are desperate to get their vision back," Nau says. Although sensory substitution techniques cannot fully restore sight, they do provide the information necessary for spatial orientation. Along with the blind, the BrainPort could help people with visual defects such as glaucoma, which leads to the loss of peripheral vision, and macular degeneration, which degrades sight at the center of the visual field.