Tuesday November 15 2011
EEG scans showed brain responses in a minority of patients
It may be possible to have conversations with patients who are in a vegetative state, The Daily Telegraph has today reported. The newspaper says new research into their brain activity has suggested they are “able to understand what is being said to them and follow commands to think certain thoughts”.
The research examined the electrical activity in 16 vegetative patients’ brains when they were asked to perform simple tasks such as wiggling their toes. Although they were unable to respond physically, measurements of their brain activity using electroencephalography (EEG) scans suggested that three were able to respond mentally to the command. When the technique was then tested in 12 healthy, conscious participants, the EEG results of three of them did not show the normal brain patterns for following the command. This result was unexplained.
This was only a small study so it is not easy to tell whether the results apply to larger groups of patients in a vegetative state. However, if it is proven to be effective in other patients it might have a role in checking whether patients who seem to be in a vegetative state actually have some level of mental function and consciousness.
Many newspapers have suggested that the method could be used to devise two-way communication systems, but this seems to be far from certain, particularly as the study only tested responses to simple commands and did not test responses to more complex messages.
Where did the story come from?
The study was carried out by researchers from the University of Western Ontario, the University of Cambridge, the Medical Research Council and hospitals in Belgium and the UK. The research was funded by the Medical Research Council, the University of Liege and a number of other research foundations.
The study was published in the peer-reviewed medical journal The Lancet.
The media reports on this research tended to focus on the potential future applications of the technique, as opposed to the diagnostic capability that was studied. While descriptions of the research were accurate, most news stories suggested that the findings could indicate that patients may one day be able to hold two-way conversations with friends and family. The BBC, however, appropriately focused on the use of the technique to aid in diagnostics rather than drawing unsupported conclusions from the research.
What kind of research was this?
This was a controlled experimental study that recruited patients diagnosed as being in a vegetative state from two hospitals in Belgium and the UK. Some of these patients suffered a traumatic brain injury (for example from a fall or a blow), while others did not (non-traumatic vegetative state may be caused by a disease process, such as a severe stroke). The study also recruited healthy individuals to serve as controls.
Controlled experiments are a useful design for early research testing a premise. Applying the same method to both injured and healthy individuals allows the researchers to assess the ability of EEG scans to detect awareness in a command-response test.
What did the research involve?
The researchers recruited two groups of individuals to participate in the study. The first group consisted of 16 patients diagnosed as being in a vegetative state with no behavioural signs of awareness. This state was the result of traumatic brain injury in five of the patients, and non-traumatic brain injury in 11 of the patients. Twelve healthy controls also participated in the research.
The researchers used a technique called electroencephalography (EEG) to measure the brain activity in each of these groups in response to commands. EEG is a simple, portable and pain-free neurological test (most commonly used in the investigation of epilepsy) where electrodes are attached to the scalp to record electrical signals coming from the brain.
The researchers applied the EEG to each of the participants and gave commands to imagine that they were clenching then relaxing their right fist or wiggling then relaxing the toes on their right foot. They then measured the activity in the areas of the brain that control movement to determine whether or not the participants were capable of responding to commands. The researchers say that command-following is a universally accepted measure of awareness, and that the task used in this study makes demands on several complex mental functions, including the ability to maintain attention, to select an appropriate response, to understand language and to use working memory.
The researchers then analysed how many participants in each group exhibited awareness as measured by the EEG. During data analysis, the researchers adjusted their results for several factors that may have accounted for the results, including age at the time of injury, time since the injury, cause of injury and diagnostic score.
What were the basic results?
The researchers found that three of the 16 vegetative state patients (19%) were aware and capable of responding to commands in a way visible when using an EEG. When responsiveness was assessed by cause of injury, they found a significant difference between the two groups, with two of the five traumatic brain injury patients (40%), and one of the 11 non-traumatic brain injury patients responsive (9%).
They further found that the EEG showed that nine of the 12 (75%) healthy controls exhibited brain activity that was classified as responsive to commands.
How did the researchers interpret the results?
The researchers concluded that this technique offers an affordable, portable and widely available alternative for confirming the diagnosis of patients in a persistent vegetative state and for detecting patients who may be minimally conscious but would not be diagnosed as such based on behavioural measures alone.
This research provides some evidence that a relatively inexpensive and easily accessible technology could have a role in diagnosing and assessing patients in a vegetative state.
At present, diagnosing a person as being in the vegetative state is normally a complex process involving various investigations and clinical assessments by expert doctors. These results suggest that EEG could potentially be used as a complementary technique performed at the bedside not only to aid in an initial diagnosis, but also to reassess whether existing patients still have some level of mental function and consciousness.
While the existing technique of EEG could potentially be used quite easily to assess patients in a vegetative state, these genuinely interesting results must still be viewed in context. The researchers tested the process in only 16 patients from two hospitals, which is unlikely to be representative of all patients in a vegetative state. Additionally, it is unclear how specific and valid this measure is of awareness, as 25% of the healthy, fully aware control participants studied were not confirmed as being aware using EEG analysis. The researchers say that this finding emphasises the importance of interpreting only positive results with this method (that is, only when some activity is confirmed) and not assuming that a negative result necessarily indicates a lack of awareness. A comment published in The Lancet along with the research points out that the lack of response in three of the healthy, fully aware controls could indicate that command-following is not an absolute measure of consciousness, and that it may measure something else.
The researchers say that the development of this technique could pave the way for communication devices in this group of patients, perhaps one day enabling them to communicate “information about their inner worlds, experiences and needs”. This particular application would require significantly more research, however, and new technological developments.