Scientists may soon be able to listen to paralysed or brain-damaged patients who cannot speak, thanks to a form of electronic telepathy.

In a study described as "quite remarkable" by leading health experts, American researchers from the University of California discovered that they're able to 'decode' unspoken words that are going on inside a person's head.

Deciphered from electronic brain waves picked up using intelligent computer technology, scientists are able to 'predict' a word from a person's mind, very much like mind reading. It is thought the same electric brain signals may record the imagined conversations we play in internal monologues in our minds.

"This is huge for patients who have damage to their speech mechanisms because of a stroke or Lou Gehrig's disease and can't speak," says Professor Robert Knight, one of the researchers from the study.

"If you could eventually reconstruct imagined conversations from brain activity, thousands of people could benefit."

Researchers made their discovery after enlisting the help of people undergoing brain surgery to investigate the cause of untreatable epileptic seizures. This involved cutting a hole into the skull of the epileptic patient and placing 256 electrodes onto the surface of the brain.

Patients were then told to listen to men and women saying individual word including nouns, verbs and names.

Brain activity from the temporal lobe was recorded in 15 seizure patients and researchers were able to listen to five to 10 minutes of conversation. Using two different computational models, researchers matched spoken sounds to the pattern of electrode activity.

Between these two programmes, synthesised sounds were produced and the most realistic sound was the one scientists used to guess the original word.

Researcher Dr, Brian Pasley compared this technique to a pianist 'hearing' the music a colleague is playing in a sound-proof room simply by looking at the keys on the piano.

"We are looking at which cortical sites are increasing activity at particular acoustic frequencies, and from that, we map back to the sound," says Dr. Pasley.

"This research is based on sounds a person actually hears, but to use this for a prosthetic device, these principles would have to apply to someone who is imagining speech.

"There is some evidence that perception and imagery may be pretty similar in the brain. If you can understand the relationship well enough between the brain recordings and sound, you could either synthesise the actual sound a person is thinking, or just write out the words with a type of interface device."

Researchers are hoping that this discovery, published in the journal Public Library of Science Biology, will help comatose and brain-damaged patients communicate without having to speak.

There were fears that scientists could 'mind read' our innermost thoughts, provoking an ethical debate. However, researchers played down these fears by saying that at the moment, this technology can only be used on people will to have surgery.

They added that this technology will continue to be invasive, as non-invasive brain scans are not powerful enough to read this level of information.

"Perhaps luckily for all those of us who value the privacy of their own thoughts, we can rest assured that our skulls will remain an impenetrable barrier for any would-be technological mind hacker for any foreseeable future," added Dr. Pasley.