It is the first time that people who cannot move a single muscle have been able to express their thoughts and feelings to their friends and family.
An international team of scientists from Germany, Italy and the United States enabled the patients to train their own brain-wave patterns to control a computer spelling device.
Neils Birbaumer, a psychologist from the University of Tubingen, and his colleagues describe in the journal Nature how they enabled two "locked- in" patients suffering from total paralysis to communicate again after years of silence.
"The system can be used by people who have no muscular control, even those who cannot control the movement of their eyes," Dr Birbaumer said.
The two patients suffer from advanced motor neuron disease and have to breathe using artificial respirators because of the complete degeneration of the nerves controlling the muscles of their bodies.
Each patient was trained to control the electrical activity of their brains, as recorded by an electroencephalogram, and to use their brain- wave patterns to control a computer program for spelling out words.
Dr Birbaumer said that it usually takes healthy patients between five and ten training sessions to control the computer's spelling accurately, using their thoughts alone.
However, it took the paralysed patients much longer, between 70 and 100 trials each lasting about five to ten minutes. "We don't know how it works. These centres in the brain for self-control are far away from the languages areas," Dr Birbaumer said.Reuse content