Like its more common (and welcome) cousin sleep, there is much we don't know about comas. Unconsciousness is a necessary and important flip side to being conscious, but much of what we know about non-awake states has to do with the ills that befall us if we don't sleep — not because we fully understand what happens when we do.

Like sleep, comas are considered a possible healing mechanism, enough so that doctors sometimes put patients into temporary deep, coma-like states to prevent brain inflammation and other issues. 

Over the last decade, there have been some advances in understanding comas, but there is still much that is unknown. What we do know is that there are types of trauma to the brain that can cause them, and coma is the body's response to injury to the brain, which can be caused by "increased pressure, bleeding, loss of oxygen, or buildup of toxins," according to WebMD.

Within each of those causal categories, there are a host of illnesses or injuries that can bring them on — high blood pressure, aneurysms and brain tumors can cause bleeding sans violent trauma, and of course, car accidents, falls and other violent experiences can bring on bleeding in the brain that causes a coma. Diabetics can go into coma from hypo- or hyperglycemia, and oxygen deprivation from choking, drowning or stroke can also trigger them. Infections of the central nervous system, like meningitis or encephalitis can also cause coma, but so can toxins: "Ammonia due to liver disease, carbon dioxide from a severe asthma attack, or urea from kidney failure can accumulate to toxic levels in the body. Drugs and alcohol in large quantities can also disrupt neuron functioning in the brain," reports WebMD.

Because causes vary, treatments vary too. They range from antibiotics to glucose to tumor removal or draining of fluid from the skull. But even after treatment, coma can continue in some people for years. It is this type of coma that can be the most mysterious and difficult to treat. And when people do wake up from them, they have a significant chance of brain damage and persistent disability.

Comas can be permanent, but they can also be reversible, and probably the most confounding thing about them is that often, doctors don't know which is which. 

A few remarkable cases include those who wake up after long periods and are able to fully recover. And in some rare cases that includes people who come out of comas able to hear and see, but who aren't able to move at all or communicate; this is called locked-in syndrome. Martin Pistorius, recently featured on the podcast "Invisibilia," was one of these. He fell into a coma at age 12, most likely from a form of meningitis, and "woke up" a couple of years later, but was unable to move or communicate.  

As he told NPR, "Everyone was so used to me not being there that they didn't notice when I began to be present again," he says. "The stark reality hit me that I was going to spend the rest of my life like that — totally alone." For a time, the negative feelings ate him up, but then he decided to change the way he thought. Changing his thoughts was part of the reason he says he believes he was able to recover, and he's even written a book about the experience called "Ghost Boy."

With the advent of functional MRI machines which measure brain waves in real time, this type of coma is now being better understood. Research that began with those who are in a minimally conscious state (MCS) — people who can use eye movements or blinks or other tiny cues to indicate they can see and hear — can be be tested for brain activity.

According to a paper by Dr. Clifford Saper from Harvard available via the Dana Foundation, "... characteristic patterns of activity within the brain can be detected when the subject is asked to imagine watching a tennis match (which, for example, engages the visual cortex). This pattern is different from what is seen in a subject who is asked to imagine walking through a house, or performing another task (which typically engages parts of the cerebral cortex involved in control of movement). Tests of this type on MCS patients  show that some demonstrate patterns of brain activation, which indicate that they are indeed processing the task using areas of the brain appropriate for that task, despite their appearance of non-responsiveness."

This initial research on people with MCS has now been extended to some people who are completely nonresponsive, and a small number have been shown to be conscious, but locked-in, just like Pistorius. "Previously, in completely paralyzed patients, there was no way to be sure if the patient was cognitively intact. Now, studies using fMRI have not only detected normal patterns of brain activation, but by allowing the patient to imagine either a tennis match (meaning a yes answer to the question) or a walk (signifying a no answer), the patients have even been able to establish a crude means of communication," Saper wrote. 

The doctor suggests that rather than assume these patients are hopeless, more longer-term trials and studies are needed, including those that include repetitive daily cognitive stimulation and/or deep brain stimulation (using electricity to stimulate uninjured brain areas). There are also several new drugs, including amantadine and zolpidem which have been shown to help some patients wake up. 

Related on MNN: 

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.