Research paves way for ‘decoding’ thoughts of brain-damaged patients

A first step has been taken towards hearing imagined speech using a form of electronic telepathy, it has been claimed.

Scientists believe in future it may be possible to “decode” the thoughts of brain-damaged patients who cannot speak.

In a study described by one British expert as “remarkable”, researchers in the US were able to reconstruct heard words from brain wave patterns.

A computer program was used to predict what spoken words volunteers had listened to by analysing their brain activity. Previous research has shown that imagined words activate similar brain areas as words that are actually uttered.

The hope is that imagined words can be uncovered by “reading” the brain waves they produce. “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,” said Professor Robert Knight, one of the researchers.

“If you could eventually reconstruct imagined conversations from brain activity, thousands of people could benefit.” However, the study involved the use of electrodes inserted through the skull on to the brains of epileptic patients. A system sophisticated enough to achieve the same result non-invasively remains a long way off. Prof Knight acknowledged the research was at an early stage and controlling movement with brain activity was “relatively simple” compared with reconstructing language. But he added: “This experiment takes that earlier work to a whole new level.”

Scientists enlisted the help of people undergoing brain surgery to investigate the cause of untreatable epileptic seizures. To pinpoint where the seizures were being generated, neurosurgeons cut a hole in the skull and placed an array of electrodes on to the surface of the brain.

In the case of 15 seizure patients, brain activity from the temporal lobe was recorded as they listened to five to 10 minutes of conversation. Two different computational models were devised to match the spoken sounds to patterns of activity from the electrodes.

Patients then heard a single word, and the models were used to predict what it was from the earlier analysis. The better of the two programmes reproduced a synthesised sound realistic enough for the scientists to guess the original word.

There is evidence that the brain breaks sound down to its component acoustic frequencies, with speech spanning the range from about 1 Hertz (cycles per second) to 8,000 Hertz.

Study leader Dr Brian Pasley said: “We are looking at which cortical sites are increasing activity at particular acoustic frequencies, and from that, we map back to the sound.”

He compared the technique to a pianist “hearing” music a colleague is playing in a sound-proof room simply by looking at the keys.

Dr Pasley added: “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.”