How Can We Tell If a Comatose Patient Is Conscious? - Scientific ...

Steven Laureys greets me with a smile as I enter his office overlooking the hills of Liège. Although his phone rings constantly, he takes the time to talk to me about the fine points of what consciousness is and how to identify it in patients who seem to lack it.
Doctors from all over Europe send their apparently unconscious patients to Laureys—a clinician and researcher at the University of Liège—for comprehensive testing. To provide proper care, physicians and family members need to know whether patients have some degree of awareness. At the same time, these patients add to Laureys’ understanding. The interview has been edited for clarity.
What is consciousness?
It is difficult enough to define “life,” even more so to define “conscious” life. There is no single definition. But of course, in clinical practice we need unambiguous criteria. In that setting, everyone needs to know what we mean by an “unconscious” patient. Consciousness is not “all or nothing.” We can be more or less awake, more or less conscious. Consciousness is often underestimated; much more is going on in the brains of newborns, animals and coma patients than we think.
So how is it possible to study something as complex as consciousness?
There are a number of ways to go about it, and the technology we have at our disposal is crucial in this regard. For example, without brain scanners we would know much, much less than we now do. We study the damaged brains of people who have at least partially lost consciousness. We examine what happens during deep sleep, when people temporarily lose consciousness. We’ve also been working with Buddhist monks because we know that meditation can trigger alterations in the brain; connections that are important in the networks involved in consciousness show changes in activity. Hypnosis and anesthesia can also teach us a great deal about consciousness. In Liège, surgeons routinely operate on patients under hypnosis (including Queen Fabiola of Belgium). Just as under anesthesia, the connections between certain brain areas are less active under hypnosis. And finally, we are curious to understand what near-death experiences can tell us about consciousness. What does it mean that some people feel they are leaving their bodies, whereas others suddenly feel elated?
What processes in the brain create consciousness?
Two different networks seem to play a role: the external, or sensory, network and the internal self-consciousness network. The former is important for the perception of all sensory stimuli. To hear, we need not only ears and the auditory cortex but also this external network, which probably exists in each hemisphere of the brain—in the outermost layer of the prefrontal cortex as well as farther back, in the parietal-temporal lobes. Our internal consciousness network, on the other hand, has to do with our imagination—that is, our internal voice. This network is located deep within the cingulate cortex and in the precuneus. For us to be conscious of our thoughts, this network must exchange information with the thalamus.
What happens in a comatose person?
The brain is so heavily damaged that neither of the networks functions correctly anymore. This malfunction can occur as a result of serious injury, a brain hemorrhage, cardiac arrest or a heart attack. At most, a coma lasts for a few days or weeks. As soon as patients open their eyes, they are said to “awaken” from the coma. This does not, however, mean that a person is conscious. Most patients who awaken from a coma soon recuperate. But a minority will succumb to brain death; a brain that is dead is completely destroyed and cannot recover. But some patients who are not brain-dead will never recover either.
How do we know whether a coma patient who has awakened is conscious?
For that we use the Glasgow Coma Scale. The physician says, “Squeeze my hand.” Or we observe whether the patient responds to sounds or touch. If patients do not respond, the condition used to be called “vegetative”; they appear to be unconscious. If a patient responds but is unable to communicate, we categorize the consciousness as “minimal.” Such patients may, for example, follow a person with their eyes or answer simple questions. If we pinch their hand, they will move it away. But these signs of consciousness are not always evident, nor do we see them in every patient. A patient who awakens from a coma may also develop a so-called locked-in syndrome, being completely conscious but paralyzed and unable to communicate, except through eye blinks.
So the difference between unresponsiveness, minimal consciousness and locked-in would seem to be hard to determine.
That’s right. If there is no response to commands, sounds or pain stimuli, this does not necessarily mean that the patient is unconscious. It may be that the patient does not want to respond to a command or that the regions of the brain that process language are so damaged that the person simply doesn’t understand me. Then there are cases in which the brain says, “Move!” but the motor neural pathways have been severed. Family members are often quicker than physicians to recognize whether a patient exhibits consciousness. They may perceive subtle changes in facial expression or notice slight movements that escape the physician’s attention.
Patients are brought to Liège from all over Europe to undergo testing. How do you determine whether they are conscious?
Well, of course, the physician will say, “Squeeze my hand”—but this time while the patient is in a brain scanner. If the motor cortex is activated, we know that the patient heard and understood and therefore is conscious. We also want to determine the chances of recovery and what the physician or the patient’s family can do. With different brain scanners, I can find out where brain damage is located and which connections are still intact. This information tells family members what the chances of recovery are. If the results show that there is no hope whatsoever, we then discuss difficult topics with the family, such as end-of-life options. Occasionally we see much more brain activity than anticipated, and then we can initiate treatment aimed at rehabilitation.
One well-known case was that of Rom Houben.
That’s right. He was a very important patient for us: as far as anyone could tell, he had been left completely unresponsive for 23 years after a car accident. But in the mid-2000s we placed him in a brain scanner and saw clear signs of consciousness. It is possible that he experienced emotions over all those years. He was the first of our patients who was given a different diagnosis after such a long time. We subsequently conducted a study in several Belgian rehab centers and found that 30 to 40 percent of unresponsive patients may exhibit signs of consciousness.
I’ve heard thatHouben was eventually able to type words with the help of his communication facilitator.
Yes, but his facilitator was the only person who seemed able to understand and translate his minimal hand signals. She probably typed words of her own unconsciously. This form of communication doesn’t generally work, and our team was wrongly connected with it. It is a complex case that the media has failed to report adequately. They were more interested in telling sensational, simplistic human-interest stories. Nonetheless, it’s a good example of why we must be extraordinarily careful in diagnosing this condition.
How can minimal consciousness be distinguished from locked-in syndrome?
Minimally conscious patients can barely move and are not completely aware of their surroundings. In other words, their motor and mental abilities are limited. Locked-in patients can’t move either, but they are completely conscious. They have suffered a particular type of injury to the brain stem. Their cerebral cortex is intact but is disconnected from their body. All they can move is their eyes—something that neither the patient nor the physician is aware of at the beginning. This is why diagnosis is so difficult. Just because patients cannot move does not mean they are unconscious. This is a classic fallacy; consciousness does not reside in our muscles but in our brains.
How can a person who cannot move manage to communicate?
To communicate with a minimally conscious patient for the first time here in Liège, we placed him in a scanner. Of course, the scanner cannot tell us directly whether someone is saying yes or no. But there are a couple of tricks. For example, we can tell the patient, “If you want to say yes, imagine that you are playing tennis. If you intend to say no, make a mental trip from your front door to your bedroom.” “Yes” answers activate the motor cortex; “ no” answers engage the hippocampus, which plays a role in spatial memory. Because these two regions of the brain are located far apart from each other, it is pretty easy to tell the difference between yes and no. From that point on, we can ask the patient pertinent questions.
What other potential techniques do you have in the pipeline?
In the future, it may be possible to read brain signals using scalp electrodes and a brain-computer interface. This would make communication much quicker and less costly than with a brain scanner. We have also found that it is possible to examine a person’s pupils: we ask patients to multiply 23 by 17 if they intend to say yes. This difficult problem causes the patients to concentrate, and their pupils will dilate slightly as a result. If we direct a camera at their eyes and a computer analyzes the signals, we can determine quite quickly whether the intended answer is positive or negative.
Anything else?
Think of the movie The Diving Bell and the Butterfly about Jean-Dominique Bauby, the editor of the French fashion magazine Elle. He suffered a stroke that left him with locked-in syndrome. He wrote an entire book—on which the movie was based—by blinking his one remaining functional eye. We are now able to place an infrared camera over patients’ eyes, which enables them to chat or write relatively easily.
Can consciousness be stimulated?
Yes, by transcranial direct-current stimulation. Using scalp electrodes, we can stimulate particular regions of the brain. By careful placement, we can select the region responsible for speech, which is connected with consciousness. If I stimulate this region of the brain, the patient may hear and understand what I say. In some cases, a patient has been able to communicate transiently for the first time after a 20-minute stimulation—by, for example, making a simple movement in response to a question. Other patients have been able to follow a person with their eyes. Although consciousness does not reside in our muscles, stimulating patients may enable them to move muscles consciously.
This technique works in about half of patients with minimal consciousness. In my opinion, this represents the future of treatment, even though we do not yet know precisely which regions of the brain are the most responsive to stimulation or whether they should be stimulated on a daily basis. But I don’t want to give people false hope. We are still faced with the question of the minimum acceptable quality of life. This is a major philosophical and ethical problem that will be answered differently by different people. I would recommend that everyone discuss these issues in advance with a trusted person. Then you will know that, if you are ever in that position, your desires and values will be taken into account.
Do you think that consciousness can be reduced to the brain alone?
We already know quite a bit about the brain processes that underlie attention, perception and emotions. There is no point in throwing this knowledge out the window. As a neurologist, I see the consequences of brain damage every day. It remains to be discovered whether the brain is the entire story. Scientific research has to be conducted with an open mind. The topic of consciousness is rife with philosophical implications and questions. As a physician, it is my aim to translate this knowledge into practice. It may be frustrating that we currently lack the tools to measure the hundreds of billions of synapses with their tangled mass of neurotransmitters. Nonetheless, I think it is a mistake to infer from this that we can never understand consciousness.
ABOUT THE AUTHOR(S)
Anouk Bercht is a science writer based in the Netherlands. She writes frequently about psychology.
Steven Laureys is a professor of neurology at the University of Liège and leads the Coma Science Group at Liège University Hospital Center. He has received numerous awards, among them the 2017 Francqui Prize, the most important Belgian science award.
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