How Brains React to Sound Can Separate Conscious From Vegetative Patients

By Valerie Ross | May 13, 2011 2:42 pm

What’s the News: A non-invasive test that measures brain waves could help doctors better diagnose whether a patient is truly in a vegetative state, according to a preliminary study published today in Science. What’s more, the results suggest that a particular pathway of communication in the brain is disrupted in vegetative patients but not patients with somewhat less severe brain damage—which could not only improve diagnosis, but help researchers better understand these tragic conditions.

How the Heck:

  • The researchers recorded the brain activity of 21 people with severe brain injuries and 22 healthy controls using an EEG, a set of electrodes placed on the scalp that pick up electrical signals generated by the brain’s neurons firing. Of the patients with brain damage, eight had been previously diagnosed as being in a vegetative state, while the other thirteen were in a minimally conscious state, meaning they retained some level of conscious awareness and ability to interact.
  • While recording the subjects’ brainwaves, the researchers played each of them a series of sounds with unexpected changes of tone (a one-time warble in the note). When healthy people and patients in a minimally conscious state heard the blip, their brain waves showed a spike that lasted around 170 milliseconds. For patients in a vegetative state, the spike lasted less than 100 milliseconds. That may not sound like much, but 70 milliseconds is a significant chunk of time when you’re looking at brainwaves.
  • The researchers made a mathematical model, combining their data with information about how different areas of the brain are connected to see what neurological processes might have led to this pattern of brain waves. Communication from the frontal cortex—a high-level brain region that’s important in decision making and rational thought—to other parts of the brain seemed to be disrupted in vegetative patients, they found.
  • In other patients and healthy controls, the surprising sound triggered auditory brain regions to send signals to the frontal cortex, which then responded by sending another set of signals. In vegetative patients, the auditory regions still sent signals to the frontal cortex—but the frontal cortex didn’t send any back.

What’s the Context:

  • Current methods of testing whether someone is truly in a vegetative state are time-consuming and often depend on judgment calls by clinicians. Up to 40% of patients in a minimally conscious state may be incorrectly diagnosed as vegetative, earlier work has found. Using objective recordings of brain activity rather than subjective assessments could make diagnosis easier and vastly reduce the number of mistakes.
  • Other researchers have also investigated ways to use brain scans to determine whether a patient is in a vegetative state, such as using an MRI scanner to pick up brain activity suggesting responsiveness in patients who can’t communicate.

Not So Fast:

  • The study was preliminary, and involved only a small number of patients. To suss out whether this test will make an effective diagnostic tool, the researchers say, more patients must be tested.

Reference: Melanie Boly et al. “Preserved Feedforward But Impaired Top-Down Processes in the Vegetative State.” Science, May 13, 2011. DOI: 10.1126/science.1202043

  • Albinuta

    That’s purely mind-blowing. 40% incorrectly diagnosed is quite a lot

  • Bruce H. Ramsay

    Hello, My Mom fell, hit her head, had brain surgery to remove the clot and ended up in a “persistent vegetative state”. I had her power of attorney and after four years the facility told me I needed to sign off on removing her nutrient intake. She died 10 days later. I never heard her say anthing past the first few months and I assume the physicians made the correct diagnosis, but I would’ve felt better with this type of more definitive test.



  • jean nutson

    I am always enthused by such progressive acts by men such as this experiments involving the most powerful tool of animals which is the brain.Iam not sure the 40% diagnosis that was made and found to be vegetative may necessarily be erroneous,there are a lot more chunk of the current human population who may be thought to be functioning correctly with their brains but are either insane or have very poor reasoning abilities, I have a very concrete reason to prove the fact that more than 80% of the current human population have a defective reasoning ability which they obviously are not aware of by themselves.I have immediate future plans of embarking on such experimental projects, with such huge specimen availabilty we have to go on with our experiments to promote healthy human species.

  • Suboxone Doctors

    I did not that our brains react to sound in this matter to help out with our conscious thoughts


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar