The team is also developing new analysis software, which they hope will allow more sophisticated types of movement. Currently, patients can navigate an e-mail program or make crude movements with a robotic arm; but they can’t perform more complex tasks, such as using the robotic arm to type on a keyboard or to eat a bowl of soup.
To accomplish such complicated movements, scientists must first create a better “decoder,” the algorithm that interprets the brain’s neural signals. When the brain prepares to move, say, a hand from left to right, millions of neurons in the brain’s motor cortex fire in a specific way. The researchers generate the decoder by asking patients to imagine moving their hand in a circle, which triggers neurons to fire as if the paralyzed limb was moving. A computer program then records and processes this information, ultimately creating a filter that translates subsequent neuronal activity into the desired actions.
But the filter still has a much more limited ability to translate information than the brain does. It uses data from hundreds of neurons rather than millions and collects information from a single part of the brain. Donohue and colleagues now are developing different types of algorithms to see which are most adaptable and make the best use of the available neural signals.
“We can test different algorithms and patients can tell us which are easiest or feel most natural,” says Leigh Hochberg, a neurologist at Massachusetts General Hospital and lead author of the study. “I suspect that if we can continue to improve the decoding from just a small area and perhaps record from multiple areas of the brain, we might be able to further improve the variety of control systems available to people.”
Other scientists are also developing ways to make brain interfaces much faster. For a patient, that could mean the difference between struggling to write an e-mail and composing one with little effort. Working with primates, Krishna Shenoy and colleagues at Stanford University in Stanford, CA, were able to quadruple rates of information transfer using a similar implant, but recording from a different part of the brain. For a human being, that would translate into typing 15 words per minute instead of just four.
Donoghue eventually plans to adapt his system to perform an even grander feat. The team is collaborating with scientists at Case Western Reserve University in Cleveland, OH, to create a device that uses signals from the brain to electrically stimulate paralyzed muscle, potentially allowing patients to move their limbs.
Not surprisingly, this is what people want the most. When Donoghue asked a patient if he would prefer to be able to make sophisticated movements with a prosthetic arm or crude movements with his own arm, he chose the latter. “The idea of reanimating his own body was much more important than how sophisticated the movement could be,” says Donoghue.