Four people who are 'locked-in' their bodies and unable to speak, move or blink have reportedly communicated with researchers during a ground-breaking mind-reading experiment - and told them that they are "happy".
The extraordinary discovery was made by a Swiss-led international team of scientists who were studying four patients left completely paralysed after being diagnosed with amyotrophic lateral sclerosis (ALS) or motor neurone disease.
The researchers repeatedly asked the patients "are you happy?" over a period of several weeks, and all four consistently answered "yes".
The study gives doctors hope of being able to communicate with others who are so paralysed that even eye movement is impossible.
Lead investigator Professor Niels Birbaumer, from the Wyss Centre for Bio and Neuroengineering in Geneva, said the team were "initially surprised at the positive responses" from the patients about their quality of life.
"All four had accepted artificial ventilation in order to sustain their life, when breathing became impossible; thus, in a sense, they had already chosen to live.
"What we observed was that as long as they received satisfactory care at home, they found their quality of life acceptable. It is for this reason, if we could make this technique widely clinically available, it could have a huge impact on the day-to-day life of people with completely locked-in syndrome."
The scientists developed a form of thought reading based on a system that measures blood oxygen levels and electrical activity in the brain.
Thinking "yes" or "no" to specific personal questions triggered changes correlating with brain activity that could be translated by a computer.
The findings, published in the journal Public Library of Science Biology, challenge the widely held view that completely locked-in patients lack the goal-directed thinking necessary to use a brain-computer interface.
Previous attempts to communicate with patients which relied solely on detecting electrical signals have failed.
More than 200 questions were prepared for each patient - three women and a man - with the help of family members.
During training sessions the patients were asked to think "yes" and "no" answers but to try to avoid imagining the words written down or spoken.
Patients were questioned for nine minutes three to four times a day.
The study even enabled the male patient to voice his strong disapproval of his daughter's marriage.
At the request of his family, the researchers asked him if he would agree to his daughter marrying her boyfriend and on nine occasions the answer was "no".
Professor John Donoghue, director of the Wyss Centre, said: "Restoring communication for completely locked-in patients is a crucial first step in the challenge to regain movement.
"The Wyss Center plans to build on the results of this study to develop clinically useful technology that will be available to people with paralysis resulting from ALS, stroke, or spinal cord injury.
"The technology used in the study also has broader applications that we believe could be further developed to treat and monitor people with a wide range of neuro-disorders."