Scientists from Cambridge University have discovered a new way to detect consciousness in vegetative patients by studying brainwaves, which could offer fresh hope for unresponsive brain damage patients and their families.
Their research, entitled Spectral Signatures of Reorganised Brain Networks in Disorders of Consciousness, is published in the journal Public Library of Science Computational Biology (PLOS One).
There are three states of consciousness affecting people who suffer a traumatic brain injury.
Patients who are in a coma are not awake, while those in a minimally conscious state are able to show clear evidence of sporadic awareness – they are able to blink, squeeze a finger or move a hand in response to questions.
In contrast, patients in a vegetative state have a severely damaged cerebral cortex, so while they are able to breath and open their eyes because their reticular activating system (which monitors wakefulness) is still working, they have no awareness of self at all.
Analysing brain activity in comatose patients
The scientists analysed the brain networks of 32 vegetative, comatose and minimally conscious patients as well as 26 healthy people with electroencephalography (EEG).
They then used a type of applied mathematics known as Graph Theory to analyse the EEG data in order to search for patterns of communication across brain regions.
In the brains of healthy people, there are "rich and diversely connected networks" of brain activity, which are lacking in the brains of patients with brain damage.
However, some of the vegetative patients were found to have brain activity patterns that are similar to those of healthy people.
These patients had previously been tested by doctors, and while the patients could not show any physical movement response to questions, if they were told to imagine doing a physical activity, for example playing tennis, the brain imaging shows that the part of the brain responsible for controlling movement would suddenly light up.
Potential for new bedside test
"Understanding how consciousness arises from the interactions between networks of brain regions is an elusive but fascinating scientific question," said Dr Srivas Chennu, a senior research associate in the Department of Clinical Neurosciences at Cambridge University, who led the research.
"But for patients diagnosed as vegetative and minimally conscious, and their families, this is far more than just an academic question - it takes on a very real significance.
"Our research could improve clinical assessment and help identify patients who might be covertly aware, despite being uncommunicative."
The scientists' research could be used to create a relatively simple bedside awareness test and unlike the brain imaging "tennis test", would not require doctors to have access to large and expensive functional magnetic resonance imaging (fMRI) scanners.
Dr Tristan Bekinschtein, from the Medical Research Council's Cognition and Brain Sciences Unit at Cambridge University, said: "Although there are limitations to how predictive our test would be used in isolation, combined with other tests it could help in the clinical assessment of patients.
"If a patient's 'awareness' networks are intact, then we know that they are likely to be aware of what is going on around them. But unfortunately, they also suggest that vegetative patients with severely impaired networks at rest are unlikely to show any signs of consciousness."