Scientists have been studying electrotactile presentation of visual information since the early 1900s, at least. These research setups typically used a camera to set current levels for a matrix of electrodes that spatially corresponded to the camera's light sensors. The person touching the matrix could visually perceive the shape and spatial orientation of the object on which the camera was focused. BrainPort builds on this technology and is arguably more streamlined, controlled and sensitive than the systems that came before it.
For one thing, BrainPort uses the tongue instead of the fingertips, abdomen or back used by other systems. The tongue is more sensitive than other skin areas -- the nerve fibers are closer to the surface, there are more of them and there is no stratum corneum (an outer layer of dead skin cells) to act as an insulator. It requires less voltage to stimulate nerve fibers in the tongue -- 5 to 15 volts compared to 40 to 500 volts for areas like the fingertips or abdomen. Also, saliva contains electrolytes, free ions that act as electrical conductors, so it helps maintain the flow of current between the electrode and the skin tissue. And the area of the cerebral cortex that interprets touch data from the tongue is larger than the areas serving other body parts, so the tongue is a natural choice for conveying tactile-based data to the brain.
Wicab is currently seeking FDA approval for a balance-correction BrainPort application. A person whose vestibular system, the overall balance mechanism that begins in the inner ears, is damaged has little or no sense of balance -- in severe cases, he may have to grip the wall to make it down a hallway, or be unable to walk at all. Some inner-ear disorders include bilateral vestibular disorders (BVD), acoustic neuroma and Meniere's disease, and the sense of balance can also be affected by common conditions like migraines and strokes. The BrainPort balance device can help people with balance problems to retrain their brains to interpret balance information coming from their tongue instead of their inner ear.
An accelerometer is a device that measures, among other things, tilt with respect to the pull of gravity. The accelerometer on the underside of the 10-by-10 electrode array transmits data about head position to the CPU through the communication circuitry. When the head tilts right, the CPU receives the "right" data and sends a signal telling the electrode array to provide current to the right side of the wearer's tongue. When the head tilts left, the device buzzes the left side of the tongue. When the head is level, BrainPort sends a pulse to the middle of the tongue. After multiple sessions with the device, the subject's brain starts to pick up on the signals as indicating head position -- balance information that normally comes from the inner ear -- instead of just tactile information.
Wicab conducted a clinical trial with the balance device in 2005 with 28 subjects suffering from bilateral vestibular disorders (BVD). After training on BrainPort, all of the subjects regained their sense of balance for a period of time, sometimes up to six hours after each 20-minute BrainPort session. They could control their body movements and walk steadily in a variety of environments with a normal gait and with fine-motor control. They experienced muscle relaxation, emotional calm, improved vision and depth perception and normalized sleep patterns.
In the next section we'll look at the BrainPort vision device.