Our sense of smell helps us enjoy freshly brewed coffee and warns us that we may have a gas leak. However, our ability to sniff aromas may also enable us to do more than assess our surroundings -- it may provide a novel way for people to communicate, new findings suggest.
Researchers have created the first device that allows people who are completely paralyzed to control a computer or maneuver an electric wheelchair simply by sniffing, according to their July 27 report in Proceedings of the National Academy of Sciences.
"This seems to be a very promising, low-cost solution for people who are severely disabled," said lead investigator Noam Sobel, a professor of neurobiology at the Weizmann Institute of Science in Israel.
Sobel and his colleagues stumbled upon the idea while studying how the brain typically processes smells. The team used an instrument that was programmed to emit odors, but noticed that people accidentally activated the device when they inhaled through their nose.
"We realized that people could potentially instruct machines to do a number of things with their sniffs," Sobel said.
Specifically, Sobel's team wondered whether people with severe disabilities, such as quadriplegia and "locked-in syndrome" -- a condition marked by complete paralysis but intact cognitive function -- could use their breaths to write letters and e-mails or control an electric wheelchair.
Sniffing requires moving the soft palate, the tissue towards the back of the roof of the mouth, which receives signals from nerves in the brain, not the spine. The researchers thought people with severe spinal cord injuries might still retain their ability to sniff.
The researchers built a "sniff-controller" that measures changes in nasal pressure when people reposition their soft palate by breathing through their nose. It's possible to produce a range of sniffs by inhaling or exhaling, taking shorter or longer breaths or breathing with greater or lesser force. The device converts these pressure changes into electrical signals that instruct a computer to do something.
Sobel's team tested the interface in 96 healthy and 15 severely disabled participants in several scenarios. All healthy participants played computer games using the sniff device to press buttons and move a mouse as adeptly as with a hand-held a mouse. They also navigated a sniff-controlled electric wheelchair and wrote full sentences on the computer simply by varying their breathing.
The researchers then tested locked-in and quadriplegic participants. After only 15 minutes of practice, all quadriplegic participants were able to use the sniff controller to drive an electric wheelchair as well as the healthy participants. Using sniff text-writing software, quadriplegic participants also wrote with ease, accelerating from 11.4 seconds per letter to 9 seconds per letter in only three tries. In comparison, healthy participants took, on average, 6.7 seconds to type each letter with sniffs.
Two of the three locked-in individuals also fared well on the tasks, including one participant who was able to communicate for the first time since her accident seven months before. The third locked-in participant failed to gain control of his soft palate.
"There will be a certain percentage of locked-in people -- an estimated 25 percent -- who will not be able to control their soft palate and for whom our solution will not work," Sobel said.
Niels Birbaumer, a professor of behavioral neurobiology at the University of Tubingen in Germany, agrees that this sniff technique may be useful for paralyzed individuals who can breathe on their own, but would not work for completely locked-in patients who require help breathing. For these patients, a brain computer interface -- a technique that allows the brain to directly communicate with a computer -- is the only alternative, he said.
To take this new technique a step further, the researchers are now working to generate more intricate software. "This could potentially help patients write faster or control their movement with greater accuracy," Sobel said.