Israeli scientists say they have may have opened a door to determining how aware unconscious people are of the sounds around them, by monitoring brainwaves.
The discovery, outlined in peer-reviewed research published in Nature Neuroscience, came as a Tel Aviv University research team analyzed the brain activity of a large cohort of epilepsy patients — specifically, the activity of waves measuring 10 to 30 Hz, known as alpha-beta waves — as sounds went on around them. While these waves have been widely researched, the focus hasn’t been on the relationship to sound.
The higher regions of the brain normally suppress alpha-beta waves in the course of their regular processing activity, reducing their quantity. But Prof. Yuval Nir and colleagues found that when people are exposed to sounds as they sleep, their brain stops doing this, a fact that wasn’t known before. Thus, sleeping people produce high levels of alpha-beta waves.
Nir’s hypothesis, based on principles from his lab’s previous research, is that a similarly high level of waves of the frequency in question will be found among coma patients who aren’t processing the sound around them. By contrast, regular levels of these waves could be shown to indicate that patients are hearing and processing sounds.
He believes that this research could pave the way for technology to assess people’s level of consciousness including, in the case of coma patients, whether they are processing relatives’ voices and other sounds around them.
Nir emphasized that this was theoretical at this stage, but said that more research conducted by his lab and others suggests that a strong inference can be drawn from brain activity in sleeping people to those in comas.
His hope is that his research will become a basis for building monitors using the power of electroencephalograms (EEGs), noninvasive devices that record brain activity, Nir said.
His research is based on data from electrodes implanted deep in human brains, which give a far more detailed view of activity than electroencephalograms.
“We worked with teams of neurosurgeons in Israel and America who treat epilepsy patients and have electrodes in their brains for days, for monitoring,” said Nir. “We utilized that opportunity, in relation to patients who gave consent, to see what happens in the brain.”
His team, which included Dr. Hanna Hayat and Dr. Amit Marmelshtein, both from Tel Aviv, as well as Prof. Itzhak Fried from the University of California Los Angeles, placed speakers emitting various sounds at the patients’ bedside.
They compared data from the implanted electrodes – neural activity and electrical waves in different areas of the brain – when patients were awake and asleep. They collected data from over 700 neurons, about 50 neurons in each patient, over the course of eight years.
Nir commented: “We hope that in the future it will be possible to accurately assess a person’s state of consciousness in various situations.
“These could include verifying that patients remain unconscious throughout a surgical procedure, monitoring the awareness of people with dementia, or determining whether a supposedly comatose individual, unable to communicate, is truly unaware of his or her surroundings.”