Test Can Calculate A Person’s Chances Of Waking From A Coma


Ben Taub


Ben Taub

Freelance Writer

Benjamin holds a Master's degree in anthropology from University College London and has worked in the fields of neuroscience research and mental health treatment.

Freelance Writer

36 Test Can Calculate A Person’s Chances Of Waking From A Coma
Using a technique called PET, it is possible to tell if a glimmer of conscious awareness remains. CandyBox Images/Shutterstock

We all know that 42 is the answer to the ultimate question of life, the universe and everything, and now it turns out the same number also holds the key to human consciousness. Researchers have discovered that by measuring the metabolic activity of a person’s brain while in a coma, they can accurately determine whether they are brain dead or still functional – and that 42 percent is the minimum level of activity necessary for a flicker of consciousness to remain.

It’s a grim subject to have to talk about, and hopefully no one reading this will ever have to make this decision, but there does occasionally come a time when we have to decide whether to pull the plug on a loved one. If and when this tragic conundrum ever presents itself, it’s important to be sure that there is no chance of a full recovery before hitting the kill switch.


However, it’s extremely hard to know whether a comatose person is in a minimally conscious state (MCS) – whereby their cognitive flame remains just about alive – or is suffering from unresponsive wakefulness syndrome (UWS), meaning this flame is all but extinguished.

Publishing their discovery in the journal Current Biology, a team of researchers report that by using a technique called positron emission tomography (PET), it’s possible to accurately distinguish between the two.

PET involves inserting radioactive atoms called radionuclides into a person’s body, and measuring the levels of gamma rays given off when they interact with certain tissues. From this, it’s possible to calculate the changes in glucose concentrations in body cells over a period of time, which in turn provides an indication of metabolic activity.

42 percent of regular cognitive activity is the minimum required for a flicker of consciousness to remain. vitstudio/Shutterstock


When performing PET scans on 131 patients with disorders of consciousness, the researchers found that the technique – which is already used to detect cancer – enabled them to correctly diagnose whether these patients exhibited MCS or UWS.

Results showed that the metabolic activity of those suffering from UWS was 38 percent of the normal level of a fully conscious person, while this figure rose to 58 percent for those in an MSC. Based on these findings, the researchers were able to predict whether or not a person would wake from their coma.

A year later, eight out of 11 patients whose PET scans showed 42 percent of normal activity had regained consciousness. As such, the study authors conclude that “42 percent of normal cortical activity represents the minimal energetic requirement for the presence of conscious awareness.”

So, perhaps now we finally know the question.


  • tag
  • consciousness,

  • PET,

  • coma,

  • minimally conscious state,

  • 42,

  • unresponsive wakefulness syndrome