In what could let severely paralysed people speak with their thoughts, scientists claim to have found evidence that the human brain speaks.
In a study, a team at University of Utah translated brain signals into words using two grids of 16 microelectrodes implanted beneath the skull but atop the brain, 'The Journal of Neural Engineering' reports.
"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 paralysed patients who cannot now speak," said lead scientist Prof Bradley Greger.
Because the method needs much more improvement and involves placing electrodes on the brain, the scientists say it will be a few years before clinical trials on paralysed people who cannot speak due to so-called "locked-in syndrome".
In their study, the scientists showed the feasibility of translating brain signals into computer-spoken words.
They placed grids of tiny microelectrodes over speech centres in the brain of a male volunteer with severe epileptic seizures. The man already had a craniotomy - temporary partial skull removal - so doctors could place larger, conventional electrodes to locate source of his seizures and stop them.
Using the experimental microelectrodes, the scientists recorded brain signals as the patient repeatedly read each of 10 words that might be useful to a paralysed person - yes, no, hot, cold, hungry, thirsty, hello, goodbye, more and less.
Later, they tried figuring out which brain signals represented each of the 10 words. 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 per cent to 90 per cent of the time.
When the scientists examined all 10 brain signal patterns at once, they were able to pick out the correct word any one signal represented only 28 per cent to 48 per cent of the time - better than chance but not good enough for a device to translate a paralysed person's thoughts into words.
"This is proof of concept. 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's something a patient might find useful.
"People who eventually could benefit from a wireless device that converts thoughts into computer-spoken spoken words include those paralysed by stroke, Lou Gehrig's disease and trauma," Greger said.