By Ralph Yeung
The brain is a beautifully complex structure. Its complexity, in part, allows us to interpret, perceive, communicate and interact with our world. But it came at a price: complexity, in our case, necessitated specialization, and specialization required an isolated and consistent environment. This made our brains fairly sensitive to insult and any damage could cause drastic consequences for cognition and consciousness.
Such is the case for many patients who have experienced brain trauma, be that in the form of physical trauma, infection, stroke, or any other number of ways you could injure your brain. It’s not difficult to imagine then, how easily and quickly someone could lose enough brain tissue to stop perceiving and interacting with their environment – to lose consciousness.
Unconsciousness is a realm of existence that is quite mysterious to science and medicine. Some of the patients who have suffered from such brain trauma are said to be in a vegetative state: physiologically alive, but cognitively absent. They are unable to respond or interact with their world, and traditionally it’s been thought they are unable to perceive
Since the widespread usage of magnetic resonance imaging (MRI), we’ve discovered that’s not always the case.
Most recently, Dr. Adrian Owen at the University of Western Ontario identified a patient who was previously thought to be in a vegetative state. Using functional MRI (fMRI), his team was able to identify that his patient was in fact, capable of communication. By extension, this patient can be said to be at least aware of his environment, and by some definitions, conscious, despite not being able to react to stimuli in any obviously observable way.
So how do we get people to “talk” via fMRI? Dr. David Andrew, professor of neuroscience at Queen’s, describes the process.
“The basic idea is to say to the patient: imagine playing tennis, while they’re in the MRI. Particular parts of their brain light up. Then they say: imagine cooking a meal. Another part lights up. Then they say: for yes, imagine playing tennis, for no, imagine cooking
The differential pattern of activation in the brain when someone thinks of two unrelated scenarios allows clinicians and scientists to recognize simple yes and no answers – assuming that patients respond to questions. It seems a little surreal, to think that these people are perceptive and clinicians are rightfully sceptical about claims of responsiveness from such individuals.
Often times, this method is also used to test a patient’s previous perception of the environment around them. For example, if a family member has told them, while they were in a vegetative state, that they have two nephews that were born after they have been in their vegetative state, the clinicians could ask whether or not the patient has nephews and how many.
Determining whether a patient in a vegetative state – or rather a minimally conscious state, according to Andrew — raises some very tricky ethical concerns. Given this capacity to ask questions of someone who is able to perceive the world, but unable to interact physically with it, what questions would one ask?
Often, as is the case of Owen’s patient, the first question asked is whether or not the person is in pain. In this case and in others, according to Andrew, the answer is typically no.
However, there are other important questions, and one in particular, which no clinician ever wants to ask of a vegetative patient.
“Do you want to die? Should we take you off life support? If they ask, they better be ready for the answer and do something about it,” Andrew comments.
There are a number of implications to the answer of this question. First, even in patients who are able to communicate more effectively than those in a vegetative state, euthanasia is a difficult ethical issue that the field of bioethics has yet to tackle. If the answer is yes, that they want to die, it would appear the only course of action for clinicians would be to do everything in their power to change the patient’s answer.
Andrew highlights another issue: “If they say yes, and they don’t have all their brain there, how can we go by [their decision]?”
The same, of course, can be said for any question a patient in this condition answers. This issue remains one of the strongest critiques about incidences of patients in a vegetative state communicating. How do we know they’re conscious enough to respond properly
There is no one area that governs consciousness in the brain, but rather the integration of many parts creates consciousness. Neuroscience is no closer at understanding how this works, and thus is unable to determine, by brain activation alone, truly, whether someone is, at least, minimally conscious.
Andrew’s research hopes to tackle the issue of brain damage from another angle. The vegetative state these patients are in can come about from various ways, one of which is stroke, causing oxygen deprivation to the highly sensitive brain tissue. As the lack of oxygen continues, brain tissue begins to die.
“What people don’t seem to understand is why the brain stem survives all that, but the higher brain burns out,” Andrew says.
Patients in a vegetative state, having suffered from say, a heart attack that stopped circulation from going to the entire brain, are physiologically still able to maintain involuntary control of their breathing, heart rate and reflexes, thanks to the seemingly unaffected functions from the brain stem. Strangely, the brain stem in many of these patients seems to be completely unaffected.
“Why does the brain stem survive stroke, even when deprived of glucose and oxygen as the higher brain? Maybe it’s getting more blood flow [from the heart], or blood flow isn’t getting cut off as much. What we found in my lab is that if you take slices of brain stem and expose them to oxygen glucose deprivation, the brain stem survives. You can hit these neurons … and they bounce right back. This really provides insight as to why patients in a vegetative state are alive, because the neurons are more resistant.”
Do the differences between resistance of brain stem neurons to harsh conditions compared to higher, cortical neurons, allow us to understand how the brain may recover from extensive trauma? It, unfortunately, is too soon to tell. There remains a problem, even if we identify what makes brain stem neurons so resistant: how can we treat damaged neurons?
For now, hope for patients in a vegetative state is that they can continue to live pain-free, and that neuroscience will continue to refine techniques to identify the patients who are conscious enough to communicate with their loved ones, so then we can free their trapped voices. •
Dr. David Andrew’s lab investigates the effects of stroke on the brain. He teaches a graduate level “Controversies in Neuroscience” course at Queen’s.