University of Utah scientists have demonstrated that planting microelectrodes on the surface of the brain can allow people to 'speak' with their thoughts.
EEG electrodes are too big and record too many brain signals to be used easily for decoding speech.
"We have been able to decode spoken words using only signals from the brain with a device that has promise for long-term use in paralyzed patients who cannot now speak," says Utah assistant professor of bioengineering Bradley Greger.
The method needs improvement, but could lead in a few years to clinical trials on paralyzed people who cannot speak due to so-called 'locked-in syndrome'.
The team placed grids of tiny microelectrodes over speech centers in the brain of a volunteer with severe epileptic seizures. They then recorded brain signals as he repeatedly read each of 10 words that might be useful to a paralyzed person: yes, no, hot, cold, hungry, thirsty, hello, goodbye, more and less.
When they compared any two brain signals – such as those generated when the man said the words 'yes' and 'no' – they were able to distinguish brain signals for each word 76 percent to 90 percent of the time.
When they examined all 10 brain signal patterns at once, they were able to pick out the correct word any one signal represented only 28 to 48 percent of the time – better than chance, but not yet good enough for a translation device.
"This is proof of concept," Greger says. "We've proven these signals can tell you what the person is saying well above chance. But we need to be able to do more words with more accuracy before it is something a patient really might find useful."
The team is now repeating the experiments with bigger microelectrode grids, using 121 micro electrodes.
"We can make the grid bigger, have more electrodes and get a tremendous amount of data out of the brain, which probably means more words and better accuracy," says Greger.