LYON France Someday, users of artificial hands may be able to play the piano, thanks to implanted devices that read and harness subtle control signals in their brain. Researchers at an IEEE bioengineering conference here last week reported advances in neural technology as well as the hurdles still ahead for delivering such capabilities.
"A prosthesis revolution is under way, and a lot of the mechanical problems are getting solved," said Nitish Thakor, a professor of biomedical engineering at Johns Hopkins University (Baltimore), speaking at one of two workshops on neural systems. "Now the challenge is linking [prosthetic devices] to the nervous system to control them in a real-time fashion."
The overall market for neural prosthetics is valued at $2.8 billion, estimates Daryl Kipke, a researcher from the University of Michigan who described work on new microarray electrodes to monitor and control brain functions.
The Defense Advanced Research Projects Agency is funding work to drive rapid improvements in the mechanical aspects of artificial limbs. That is fueling a need for better electrodes, electronics and algorithms to capture control information from the brain to drive the mechanical devices.
"The whole system of a prosthetic hand is a vast research area, with many fields in- volved," said Thakor. He described advances in algorithms that could let someone control basic functions, such as picking up a glass, with signals from an electroencephalogram (EEG) monitor worn on the scalp. Finer controls, such as playing a piano, would require a high-performance neural microarray sensor implanted in the brain--a development that's on the horizon, Thakor said.
"The buzz is that neural technology is today where cardio technol-ogy was 20 or 30 years ago," said Kipke. "The brain-computer interface is about to be defined as we come to understand its components."
Thakor said his group has been able to achieve 99 percent accuracy in correlating the flexing of a single finger with signals from as few as 30 neurons in the M1 area of the brain's motor cortex. "But we will need to monitor many more neurons to manage more-complex tasks" and multiple fingers, he said.
Scalp-worn EEG sensors with as many as 128 electrodes do not appear to be adequate to separate the source material into control signals for an individual finger, Thakor said.
"There appears to be no specific linear correlation of signals to the flexion movement of multiple fingers. The data is all jumbled up," he said. "So my bias is to shift the problem to mathematical algorithms be- cause the electrical problem is so daunting."
Researchers are using various worn and implanted devices to read and analyze brain signals at frequencies ranging from 1 Hz to 10 kHz.
"It will be an interesting debate over the next several years to determine which of these techniques is best. Perhaps all of them are good," Thakor said. "Ultimately, the decision of what to use will be based on ethical, surgical and clinical issues, although we as engineers may want to decide based on what gives us the best signals."
A key issue for implants is how best to capture signals.Electrode arrays are used extensively today for short-term work in animals, but researchers foresee improvements that could make the devices practical for long-term use in humans.
"I think we can cross that gap," said Michigan's Kipke. "The move of brain-computer interfaces from academic to commercial technology is critical in transferring this technology to clinical use."
Kipke is chief executive of NeuroNexus Technologies, a startup spun out of his research center three years ago to develop silicon microarrays for use in humans. Eighteen months ago, the startup began developing polymer-based arrays as well.
Products aimed at short-term diagnostic use in humans will go into testing in less than a year, said Kipke, but arrays geared for use in long-term implants will take longer to bring to market.
Other startups, including Northstar Neuroscience and Neuropace, are developing similar arrays.
Microarray developers need to find ways to reduce both damage to cells and the immune system when the arrays are inserted into brain tissue.
Kipke's group has developed a fast insertion process that can minimize cell tearing, which creates cellular debris and reactions based on chemicals released. The center is training neural surgeons in its array-insertion techniques.