An approach has found two people in an apparent vegetative state that may be conscious but “locked-in”. Getting people with brain injuries to do maths may lead to better diagnoses.
People who are in a vegetative state are awake but have lost all cognitive function. Occasionally, people diagnosed as being in this state are actually minimally conscious with fleeting periods of awareness, or even locked-in. This occurs when they are totally aware but unable to move any part of their body.
It can be very difficult to distinguish between each state, which is why a team of researchers in China have devised a brain-computer interface that tests whether people with brain injuries can perform mental arithmetic – a clear sign of conscious awareness.
The team, led by Yuanqing Li at South China University of Technology and Jiahui Pan at the South China Normal University in Guangzhou showed 11 people with various diagnoses a maths problem on a screen. This was followed by two possible answers flickering at frequencies designed to evoke different patterns of brain activity. Frames around each number also flashed several times.
The participants were asked to focus on the correct answer and count the number of times its frame flashed. The brain patterns from the flickering answers together with the detection of another kind of brain signal that occurs when someone counts, enabled a computer to tell which answer, if any, the person was focusing on.
Two of six participants diagnosed as being in a vegetative state, one of three people in a minimally conscious state and two people who had recently emerged from a minimally conscious state were able to correctly communicate their answers to the sums with accuracies that could not have occurred by chance.
Li’s results suggest that the people diagnosed as being in a vegetative state who answered correctly may well be locked-in. “Theoretically, we have changed their diagnosis,” he says. “The patients’ families were very happy when they found out that the patient could do maths,” says Li. “It made them hopeful that they would be able to be rehabilitated.”
Maths is a useful way of identifying awareness in someone with a brain injury, says Li, because the ability to do calculations uses so many different areas of the brain, including those involved in language, memory, vision and decision-making.
It isn’t totally fool proof though. Although a correct answer suggests awareness, it isn’t possible to draw any firm conclusions from an incorrect answer. The computer might register a fail because the participant has no awareness, or because they could only follow some, but not all, of the commands.
Reference: BMC Neurology, doi.org/bbkb