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Detecting Consciousness in the Vegetative

People in a vegetative state, usually as a result of brain trauma or anoxia (lack of oxygen) by definition have no signs of conscious awareness or activity. The definition, therefore, is based largely on the absence of evidence for consciousness.

Of course, arguments based upon the absence of evidence are only as compelling as the degree to which evidence has been properly searched for. In recent years technology has advanced to the point that our ability to detect the possible subtle signs of consciousness in those presumed to be vegetative has increased – mainly through functional MRI scans (fMRI) and electroencephalograms (EEGs).

There has been a steady stream of studies demonstrating that a small minority of patients thought to be vegetative actually display some signs of minimal consciousness. The latest such study was recently published in Neuroimage: Clinical by a research team from the University of Cambridge.

But let’s back up a bit first. Even prior to evaluating vegetative patients with fMRI and advanced EEG techniques, several studies showed that a detailed neurological exam specifically designed to detect the most subtle clinical signs of consciousness could find such signs in some patients who were diagnosed as being vegetative by more standard neurological exam. According to one study as many as 41% of patients diagnosed as vegetative were really minimally conscious, meaning they had subtle signs of consciousness, but still cannot wake up, converse, or act purposefully.

Other studies have shown that use of a bedside EEG is a cheap and portable option for properly detecting patients who are minimally conscious rather than vegetative.

Then fMRI began shining an intriguing light into the brains of some of these patients. One early study used fMRI to image the brain activity of an apparently vegetative patient when asked to imagine themselves playing tennis or walking around their home. The researchers were able to show that the patient would demonstrate the appropriate pattern of brain activity (compared to the established baseline) when later asked to repeat the task.

This was a stunning finding, and has later been replicated in other patients. The current study falls into this category. The researcher examined the brains of eight healthy controls while performing the task of listening to a stream of words and counting the number of times the word “yes” or “no” appeared. They then repeated the task with 21 vegetative patients. Of those, 17 showed no brain activity at all, three showed brain activity but it appeared to be random, and one patient displayed brain activity similar to that of the eight healthy controls.

The results of this study suggest that one of the 21 vegetative patients was able to direct their attention at the task in a way that was indistinguishable, by fMRI, from a healthy person.

While extremely interesting, the big question remains – what does all this mean?

The first question we always have to ask is if these results are reliable, or could they be due to an artifact or some error in the protocol. fMRI technology is still very tricky to use, and notoriously produces false positive results when not used carefully.

The results have been replicated enough, however, that at least they should be taken very seriously. There is also another reason to accept the results are probably real. One interesting pattern that has been fairly consistent in the research is that those in a vegetative state from trauma are more likely to demonstrate signs of consciousness than those resulting from anoxia.

This makes sense in that anoxia damages the entire brain, and such diffuse injury does not leave much potential for residual brain activity. Brain trauma, however, can be very non-uniform. There may be parts of the brain relatively spared and still able to participate in consciousness. Further, trauma may cause focal damage resulting in paralysis or sensory impairment that hides signs of consciousness.

Assuming, therefore, that the results are real, what are the implications? From a theoretical point of view, what we want to know is – what is happening inside the mind of those people who appear vegetative but have fMRI activity in these studies? This is the one thing we really want to know, but just can’t at this time.

The fact that the brain is showing activity in response to environmental stimuli, even abstract stimuli such as instructions to pay attention or imagine oneself playing tennis, does not mean that the person is experiencing that activity. We still may only be witnessing some component of attention or information processing without the brain being able to generate sufficient activity to produce anything that can reasonably be considered consciousness.

This is, in fact, what I strongly suspect. Further I believe this is a reasonable default assumption lacking compelling evidence to the contrary.

From a practical point of view, what do the results of this research mean? Is there a difference in prognosis or response to treatment for those who display fMRI activity vs. those who do not? The answer so far is probably not and no, respectively.

While it is true that those in a minimally-conscious state have a very small potential to experience modest neurological recovery, while those who are truly in a vegetative state have no possibility of any meaningful recovery, this difference is slight and has practical implications for only the very rare patient.

There are also currently no effective treatments for those who are vegetative or minimally conscious. The hope is, however, that treatments may be developed. In that case, the minority of vegetative patients who do show brain activity may be the ones to benefit from potential future treatments.

One such treatment involves implanting computer chips (or electrodes attached to computer chips) that enhance the activity of the parts of the brain involved in consciousness and wakefulness. fMRI technology may help us identify the minority of patients who could potentially benefit from such a treatment.

Another potential development that is often discussed in news reports of this fMRI research is the use of the technology to communicate with those who are vegetative but have brain activity. I am highly skeptical of this potential, however. It is certainly reasonable to research this to discover what the potential is, but I would recommend extreme caution.

As I stated above, the fact that the brain can respond to stimuli does not necessarily mean that there is a conscious mind present capable of communication. Further, the risk of such research is that non-specific or random responses will be over interpreted as communication – something we have seen with every research program into communicating with those who cannot communicate normally, including animals and those with cognitive impairments.

No such study has been attempted so far, and I am curious to see the protocols and results.

Conclusion

Using advanced EEG and fMRI technology to study the brains of those who appear to be vegetative is an exciting development that promises to teach us something about brain function and consciousness. This research further holds out the promise of identifying patients who may benefit from yet-to-be-developed technology.

At the very least it can reassure families that their loved-ones have been thoroughly examined and properly diagnosed. For those patients who demonstrate no brain activity at all, the family does not have to worry that they are actually locked in, or that they are prematurely abandoning hope for recovery. Proper diagnosis and prognosis is essential when dealing with the comatose, and this technology will greatly enhance the reliability of diagnosis.

Those patients who do show some brain activity despite appearing vegetative are now in a diagnostic gray zone. There is an indication of brain activity, but we just do not know yet what to really make of it. This is truly an area requiring further research.

Posted in: Neuroscience/Mental Health

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