Researchers have developed a new non-invasive brain-computer interface that can decipher the thoughts of people who are unable to communicate -- such as those living with completely locked-in syndrome -- by measuring the changes in blood oxygen levels in the brain.

Patients suffering from complete paralysis, but with preserved awareness, cognition, and eye movements and blinking are classified as having locked-in syndrome. If eye movements are also lost, the condition is referred to as completely locked-in syndrome.

"Restoring communication for completely locked-in patients is a crucial first step in the challenge to regain movement," said John Donoghue, Professor at the Wyss Center for Bio and Neuroengineering -- a Switzerland-based not-for-profit foundation.

The technology could be further developed to treat and monitor people with a wide range of neuro-disorders such as ALS, stroke, or spinal cord injury, the researchers said. For the study, appearing in the journal PLOS Biology, extensive investigations were carried out in four patients with ALS (amyotrophic lateral sclerosis, also known as Lou Gehrig's disease) -- a progressive motor neuron disease that leads to complete destruction of the part of the nervous system responsible for movement.

In the trial, patients with completely locked-in syndrome were able to respond "yes" or "no" to spoken questions, by thinking the answers.

The brain-computer interface used near-infrared spectroscopy combined with electroencephalography (EEG) to measure blood oxygenation and electrical activity in the brain.

Counter to expectations, the participants in the study reported being "happy", despite their extreme condition. "The striking results overturn the theory that people with completely locked-in syndrome are not capable of communication. We found that all four patients we tested were able to answer the personal questions we asked them, using their thoughts alone," explained Niels Birbaumer, Professor at the Wyss Center.