It's a fate that's only comparable to death. The coma, typically the result of a massive head injury or drug overdose, is a medical condition that continues to frustrate physicians, while also causing great anguish for friends and family members. But neuroscientists are starting to understand the condition a bit better — even catching a glimpse of what it's like to be trapped in a vegetative state.
Top image from the Sony Pictures 2012 miniseries, Coma.
The comatose state
Simply put, a coma is a deep and profound state of unconsciousness from which a patient cannot be woken.
A person in a coma is not brain dead — far from. In brain death, both conscious and cognitive functions have permanently ceased, what is typically the result of excessive damage to the cerebral neurons after the brain has been starved of oxygen. A comatose patient, on the other hand, is alive but completely unable to move or respond to their environment.
As far as neuroscientists can tell, patients in a coma have lost their thinking abilities and are utterly unaware of their surroundings; it's as if they're fast asleep. Comatose individuals are unable to respond to painful stimuli (like pin pricks or pinches), light, or sound. They're also unable to voluntarily move their bodies, feel, speak, or hear.
Recently, functional neuroimaging has provided new insights into the cerebral activity of patients in comas caused by severe brain damage. Unlike some patients in a vegetative state — a related condition we'll review in the next section — comatose patients do not exhibit any kind of neural patterns that would indicate conscious awareness, even after various forms of stimulation.
At the same time, however, comatose patients still have their non-cognitive capacities. They're able to breathe on their own, and their organs and blood circulation continues to function without external intervention. And they often twitch and move involuntarily.
Comas rarely last more than a month. It's more common than not for a patient to emerge from a coma after a few days or weeks. But in some unfortunate instances the comas persist. This scenario is often referred to as a vegetative state.
Most people who emerge from comas claim that they don't remember a thing — it's as if they were in a deep sleep. But some former comatose patients, like Geoffrey Lean and Aubrey Allyn, claim that they were conscious the entire time — they were just not able to control their bodies and wake up.
Even worse is the account of Rom Houben, a Belgian man misdiagnosed as being in a coma for 23 years — but was fully conscious the whole time. It turned out that he wasn't comatose at all — he was paralyzed, but unable to move or communicate. After successful treatments to alieviate the paralysis, he had this to say:
All that time I just dreamed of a better life. Frustration is too small a word to describe what I felt. I screamed, but there was nothing to hear. I shall never forget the day when they discovered what was truly wrong with me – it was my second birth. I want to read, talk with my friends via the computer and enjoy my life now that people know I am not dead.
The vegetative state
Indeed, as these accounts show, and as new technologies are revealing, there's a kind of grey area when it comes to comas. It's becoming evident that there is not just one kind of coma. Patients can have profoundly different experiences.
Take a person in a vegetative state, for example. This is a type of coma in which a patient does not emerge from unconsciousness — at least not fully. Some of these individuals are able to exhibit a higher degree of functioning. They often give the impression of a patient who is emerging from a coma. But unlike a person in a full coma, a vegetative patient is in a state of partial arousal, but still lacking in true or full awareness.
Neuroscientists describe two categories for being in a vegetative state. Four weeks after entering a coma, a person is declared as being in a persistent vegetative state. But after one year, they're re-classified as being in a permanently vegetative state.
All this said, there's no real consensus on the line that divides a comatose from a vegetative patient. The terms are often used interchangeably.
In terms of potential ‘functioning,' patients in a vegetative state are often seen to make spontaneous movements. Their eyes may open in response to some external cues. Or they occasionally grimace, cry, and even laugh. But these movements tend to be unpredictable, and they're completely unable to speak or respond to commands.
But as already noted, there may be more going on inside their minds than meets the eye.
Indeed, as recent insights by neuroscientists working at Western University in Ontario have revealed, it is in fact possible to communicate with some patients locked in a vegetative state by using an fMRI scanner. It's a remarkable breakthrough which suggests that more meaningful dialogue with vegetative patients may be possible.
And in fact, just last month a team of neuroscientists used the same technology to communicate with a man in a vegetative state. He was able to relay information to them about his condition, saying that he was not in any pain. Though no verbal communication was relayed, the neuroscientists were able to understand him by studying and mapping the neural patterns flashing on their screen (for example, thinking ‘yes' produced a different neural signature than thinking ‘no').
Future refinements to the technology will likely increase the sophistication of communication efforts. It's conceivable that very basic dialogue may someday be possible.
Of course, neuroscientists and medical practitioners would never dare to ask a patient the all-important question: "Do you wish to keep on living?" Bioethics boards would have a conniption over this. And arguably it could be interpreted as a violation of the Hippocratic Oath — though a strong case can be made to the contrary.
But eventually, given the potential for full communication, patients may eventually bring up the topic themselves.
The neuroscience of the coma
In terms of the science, comas can come about for any number of reasons, including the result of a serious head injury, intoxication (like a drug overdose), central nervous system diseases, metabolic abnormalities, strokes, and hypoxia (oxygen deprivation). Comas can also be induced deliberately with pharmaceuticals — what's done to shield patients from intense pain during the healing process.
Comas brought about by physical injuries occur when there's been damage to the ascending reticular system (either temporarily or permanently), or when there's been substantial damage inflicted across both cerebral hemispheres.
The ascending reticular activating system is what transmits messages to the limbic system and the hypothalamus. It also triggers the release of hormones and neurotransmitters. And crucially, it also facilitates functions like learning, memory — and wakefulness.
When much or both of the cerebral hemispheres are damaged, what's referred to as diffuse axonal injury (DAI), the trauma occurs over a more widespread area than what's experienced in a concentrated brain injury. In these cases, a person suffers extensive lesions to their white matter tracts — a central part of the nervous system that's made up of neural cells and axons. It's these brain regions that transmit signals from one area of the cerebrum to another, and between the cerebrum and lower brain centers. This type of damage is one of the major causes of unconsciousness, comas, and persistent vegetative states. And when severe enough, it can also result in death. Approximately 90% of patients with severe DAI never regain consciousness, and those who do tend to experience severe cognitive impairments for the rest of their lives.
Perhaps surprisingly, poisoning accounts for nearly 40% of comas. In these cases, toxic agents like narcotics, tranquilizers, and alcohol depress the nervous system. They can also damage or weaken the synaptic functioning of the ascending reticular system — this is what prevents arousal.
An overdose can also render a person unconscious to such a degree that breathing stops, resulting in anoxic brain injury, or what is also called cerebral hypoxia. As noted, lack of oxygen can cause crucial brain cells to undergo severe and widespread necrosis. Anoxic brain injuries can also be brought about by such things as drowning, suffocation, glucose shock, carbon monoxide inhalation, and even electric shock.
Are there any treatments?
Like any kind of medical emergency, time is trauma. As the American Academy of Neurology states, "The earlier the process inciting the comatose state is treated, the greater the likelihood of a more rapid complete recovery."
Patients who have suffered a serious anoxic episode are typically rushed to intensive care and put on a ventilator, usually in a specialist neurosciences center. Drugs may be administered to maintain adequate blood pressure and normal heart beat, while CT scans can give doctors a sense of the damage. At this stage patients may suffer seizures.
In some cases, patients may undergo medically induced cooling, called therapeutic hypothermia. This creates a protective effect on the brain and facilitates recovery by decreasing the oxygen and energy requirements of brain cells. And in fact, this may explain why some people survive after surprisingly long periods of immersion in very cold water.
Once a patient's proximate injuries have been treated and their condition stabilized, there's not much more that medical professionals can do. Caregivers at this point have to prevent infections such as pneumonias, bedsores (decubitus ulcers) and provide a balanced diet via feeding tubes.
Some patients in a coma can become restless or go into convulsions. In these cases, medicines can be administered to calm them, and side rails put on beds to keep them from falling.
Physicians also use the Glasgow Coma Scale, a neurological metric that allows them to record the severity of their patients' unconscious state.
In addition, researchers at the Belgian National Fund for Research are working to develop a numerical measure of consciousness by pulsing the brain of vegetative patients with a brief electromagnetic wave, and then measuring any neural responses using electrodes applied to the scalp.
As for efforts to bring patients out of a comatose state, the science is not quite there yet. Doctors will try to reverse the cause of the coma depending on the nature of the injury. So for glucose shock, for example, patients are often administered sugar. And as already noted, therapeutic hypothermia can also be initiated.
Interestingly, some patients who were thought to be in an unrecoverable vegetative state are awakening after being administered a $5 over-the-counter sleeping pill called zolpidem. This pill seems to be invigorating brain cells that were once thought to be dead.
As a concluding note, it's clear that physicians need to be more conscientious about determining the degree of conscious awareness in their comatose patients. For those friends and family members who cling to the hope that that their loved ones will soon wake up, there's nothing wrong with talking and touching — and in fact, for comatose patients who have some awareness, it may mean a great deal.
- National Institutes of Health
- American Academy of Neurology
- Coma Decision Algorithm
Images: Sony Pictures, S.Pytel/Shutterstock, GWImages/shutterstock, Guardian/MRC, BBC.