Previous research has shown that the device can help squirrel monkeys that had part of their vestibular system rendered dysfunctional. When the device was turned on, the monkeys’ vestibuloccular reflex improved, meaning that they could better keep their eyes stable while their heads moved. (So far, the researchers have targeted only one of the canals with their prosthesis. Other scientists working in the field have targeted all three canals in rodents.)
The team now wants to determine how well the device can treat other symptoms of vestibular disorders, such as balance and perception. (The brain uses information from the vestibular system to control both the muscles that move our eyes and the postural muscles that keep us upright.)
Measuring these senses has proved hard to do, even in humans. We manage our vestibular system–unlike vision or hearing–largely unconsciously, making it difficult for people to quantitatively report what they perceive, says Christopher Platt, who oversees balance and vestibular research at the National Institute on Deafness and Other Communication Disorders. So Merfeld and Lewis will test their prosthesis in the rhesus monkey, which can be trained to perform complex tests. To test balance, for example, the animals are taught to stand with one limb on each of four small platforms that individually move around, giving the illusion of an earthquake. Then the researchers measure the animal’s ability to maintain balance in response to the movements. To measure perception, animals are taught to turn a steering wheel to vertically orient a line on a computer screen. Without other visual cues, a monkey or person without vestibular function will orient the line at the same angle as the head.
“That’s very important because it means they can test the monkeys with exactly the same tests they give to humans, and get a better estimate of how well their device is doing, with the hope it can be transferable in humans,” says Platt.
If all goes well in initial experiments, the researchers hope to increase the complexity of the device, targeting all three canals of the inner ear, and eventually other structures. Neither Merfeld’s group nor others working in the field have yet targeted a second set of vestibular structures, the otolithic organs, which sense the head’s linear acceleration.