I've written a news story for New Scientist about a recent study which shows that patients in the minimally conscious state may be capable of dreaming, and that studying the brain wave patterns associated with sleep could be helpful in distinguishing minimally conscious patients from those in the vegetative state.

Accurate diagnosis of these mysterious conditions can help relatives make difficult decisions, because minimally conscious patients are more likely than vegetative ones to show some degree of recovery. Diagnosis can be difficult, however, and up to 40% of patients are diagnosed wrongly. It had been thought that vegetative patients were completely unaware of their surroundings, but this view began to change about five years ago, following the publication of a landmark 2006 study led by Adrian Owen.



Owen's pioneering research shows that some patients who were previously thought to be completely unconscious are in fact aware of both themselves and their surroundings. It also shows that much-maligned brain scanning technology can be used not only to aid diagnosis by detecting hidden signs of consciousness in vegetative patients, but also, in some cases, to enable them to communicate.

In the 2006 study, Owen and his colleagues used functional magnetic resonance imaging (fMRI) to investigate if a 23-year-old woman in a persistent vegetative state would respond to a series of pre-recorded spoken statements. Owen and his colleagues found that the statements produced brain activation patterns that were very similar to those observed in healthy volunteers, in regions known to be important for the processing of speech.

While the woman was in the scanner, they also told her to imagine playing tennis or walking through her house and found that her brain responses were indistinguishable from those seen healthy volunteers. When she thought about playing tennis, the supplementary motor cortex, which is involved in planning movements, became active, but when she imagined walking through her house, the parahippocampal gyrus, which is needed for spatial navigation, was activated.

Since then, another group of researchers has shown that some minimally conscious and vegetative patients can learn simple associations, and that the ability to do so is strongly associated with subsequent recovery. And last year, Owen's group confirmed their earlier findings in a larger group of patients. This more recent study also demonstrated that the mental imagery tasks could be used to obtain "yes/no" answers from the patients.

Owen's group performed fMRI on 54 minimally conscious and vegetative patients, and told them to imagine playing tennis if they wanted to answer "yes" and to imagine navigating the streets of a familiar city if they wanted to answer "no". Five of the patients were capable of answering the questions correctly in this way. All five had been diagnosed as being in a vegetative state, and only two of them responded to behavioural tests of awareness.

The failure to find positive responses in the rest of the patients cannot be taken as evidence of lack of awareness, though. It may have been because their responses were too small to be detected by the scanner, or because some of the patients may actually be permanently unconscious, or slipped into unconsciousness temporarily during the scanning.

I contacted Owen with a few questions so that I could quote him in the news story. Here are his responses:

Mo Costandi: This new study implies that minimally conscious patients may be capable of dreaming. Is this plausible?

Adrian Owen: It is certainly possible, although one has to be very careful about making such inferences. Just because minimally conscious patients show the same patterns of brain activity that are seen when healthy people dream does not necessarily mean that the patients are dreaming. This error of logic is known as a reverse inference in science and very often reverse inferences are shown to be entirely flawed. By analogy, most conscious people open their eyes during the daytime and go to sleep at night. Most vegetative patients do the same, but this does not mean that most vegetative patients are conscious. The logic is the same, and similarly flawed.

MC: Do you agree with the authors' suggestion that sleep electrophysiology could be used to distinguish between the minimally conscious and vegetative states?

AO: The authors state that sleep electrophysiology could be "helpful" in distinguishing between minimally conscious and vegetative states. That may be true and the data presented here are certainly interesting in that regard. However, they do not present evidence that sleep electrophysiology can do any better at distinguishing between these different conditions than existing methods. That is not a criticism because I do not think their intention was to come up with a new way of distinguishing between these different conditions; if that had been their intention then they would have shown evidence that their method can do better than other methods such as behavioural testing.

Their intention was to investigate how sleep processes differ in the vegetative and minimally conscious states and it is interesting that they have shown that vegetative patients do not show the normal patterns of electrophysiological change during sleep, while minimally conscious patients do show normal patterns of change. This fits with the behavioural profile of these patients; that is to say, vegetative patients showed no evidence of normal consciousness while minimally conscious patients do at least show some evidence of conscious processing.

MC: What's your overall opinion of this study? Does it have any drawbacks?

AO: I don't think there are any particular drawbacks. The sample size is quite small but this was a complicated study and it is incredibly difficult to test patients in these complex conditions. For the purposes of their conclusions I think the sample size is acceptable. Perhaps when they have tried this technique on much larger numbers of patients they will be able to show that assessing sleep electrophysiology has other advantages; for example, perhaps it can assist with prognosis, although future studies will have to look into this.

MC: Is there a consensus on how coma, minimally conscious state and vegetative state are defined and diagnosed? And is each associated with a different outcome/prognosis?

AO: Yes, there is a consensus on how coma, minimally conscious state and vegetative state are diagnosed and each is associated with a different prognosis. There are widely accepted diagnostic criteria for each of these conditions and in most countries these criteria are accepted and used. However, there is still a very high rate of misdiagnosis because it is easily possible to miss important signs (for example, fleeting signs of consciousness) and this can lead, for example, to minimally conscious patients being incorrectly diagnosed as vegetative.

MC: Can these conditions be thought of as existing along a continuum, according to the level of awareness/consciousness that is present in each?

AO: Until recently, this was presumed to be the case. That is, it was assumed that coma patients had no sense of awareness/consciousness, minimally conscious patients had at least some level of consciousness (although not enough to be able to communicate reliably) and vegetative patients were also presumed to be entirely unaware. Our paper which appeared in Science in 2006 showed that the prevailing view, at least as far as vegetative patients are concerned, is categorically incorrect.

We now know from that paper and from our follow-up papers that close to 20% of patients who are thought to be vegetative are actually conscious, but are nevertheless incapable of demonstrating their consciousness through standard clinical assessments. To date only fMRI has proven itself to be a reliable method for identifying such "covert consciousness" in this unusual population of patients, although we and other groups are working to see whether electrophysiological methods can be used for the same purpose.

There is no doubt that minimally conscious patients have some level of awareness (indeed, that is part of their diagnosis), and that assumption has not been changed by new imaging methods. Very few coma patients have been assessed using these new techniques, mostly because the practical and clinical complexities of scanning critically ill patients are very difficult to overcome.

However, this is all about to change. One of my main goals in moving my research group to Canada is to apply the techniques that we have developed for assessing long-term vegetative patients (and showing that some of them are in fact conscious) to coma patients in the intensive care unit. Who knows, perhaps we will find something similar.

References: Landsness, E, et al (2011). Electrophysiological correlates of behavioural changes in vigilance in vegetative state and minimally conscious state. Brain, DOI: 10.1093/brain/awr152

Monti, M. M., et. al. (2010). Willful modulation of brain activity in disorders of consciousness. New England Journal of Medicine, DOI: 10.1056/NEJMoa0905370

Owen, A, et al (2006). Detecting awareness in the vegetative state. Science, DOI: 10.1126/science.1130197