The experience of being in a coma has raised questions about the human brain and body for centuries. Described in various ways since Hippocrates, the phenomenon was once compared to the natural state of being asleep (via Brain). It’s no surprise then that the term is derived from the Greek word "koma," which literally translates as "deep sleep." The ancient term for coma originally meant "being struck with violence" and could be likened to the word "stroke."
From a medical point of view, a coma is defined as a state of prolonged unconsciousness, which can be caused by temporary or permanent damage to the brainstem (via StatPearls). The comatose state differs from individual to individual, but there are a few characteristics that show up frequently. Although there have been some major scientific and medical breakthroughs in the understanding of the root cause and mechanisms of coma, it remains somewhat shrouded in mystery (via Qualitative Health Research). So, what actually is going on in the body when it’s in a coma?
There are different types of coma
Not all comas are the same, as there are different forms of unconsciousness. A vegetative state is a specific type of coma where an individual has no awareness of themselves or the environment around them (via World Journal of Radiology). They’re unable to communicate or react to external stimuli. Unlike a coma — where the patient is fully unconscious — a person in a vegetative state may open their eyes at some point, blink, and look as if they might be awake, yet they don’t show any real signs of cognitive or emotional processing, according to the Brain Foundation.
Locked-in syndrome (also referred to as pseudocoma) is a neurological condition in which the person is actually conscious and cognitively intact, but cannot talk or move due to muscle paralysis in the body (via the Journal of Neurology, Neurosurgery, and Psychiatry). They can, however, voluntarily open their eyes and communicate with blinking and vertical eye movements. Likewise, those in a catatonic state appear to be conscious, yet remain unresponsive to external stimuli. Often, they may appear frozen with their eyes open, like a mannequin. Individuals who seem unconscious but can still be awoken with some effort aren’t technically in a coma. This is called a state of stupor, where a person usually sits or lies down motionless for long periods of time.
What happens in the comatose brain?
When a person is in a coma, they’re unresponsive to the outside world. It’s almost as if consciousness and awareness have been switched off. Scientists suggest that this happens when the brain’s reticular activating system (RAS) is damaged — the bundle of nerves that sits at the brainstem and regulates sleep-wake transitions (via Brain). Many studies have shown that a comatose person’s brain doesn’t exhibit the same patterns of activity observed during wakefulness (via World Journal of Radiology). Despite the existing research, however, substantial gaps remain in coma understanding. The researchers of a 2013 study published in PLoS ONE discovered some brain activity in the hippocampus of an epileptic man in a coma, pointing out that even though the brain isn’t functioning normally, it may be undergoing a process of self-healing and preservation.
Research that has looked at the brains of people in vegetative states also detected activity in some regions of the cortex (via Trends in Cognitive Sciences). It’s believed that the brain can still respond to external stimulation and sensations such as pain, which appears to activate the primary sensory cortices receiving input from the outside world. However, these areas are disconnected from the higher-order regions involved in awareness.
The shift from a coma to brain death
A coma is not the same as brain death. A person in a coma is in a deep state of unconsciousness due to a brain injury or a severe illness, like a heart attack or stroke, according to Johns Hopkins Medicine. They’re unable to open their eyes, speak, or respond, but they’re still alive. The brain isn’t fully damaged, and many basic bodily functions, such as respiration and blood circulation, continue to tick on. Brain death can occur when brain activity and function start to shut down and irreversibly cease. The heart may continue to beat as the lungs receive oxygen from a ventilator, but unlike in a coma, a person who is brain dead has no chance of waking up or being revived.
Since the brain is no longer working, the patient’s breath will also stop once the ventilator is turned off. A person in a coma may or may not deteriorate to the point of brain death (via Indian Journal of Critical Care Medicine). That being said, the transition isn’t always immediately obvious to those without medical training.
Your body just keeps on doing its thing
What makes a coma particularly fascinating is that despite being in a dormant state, many bodily functions continue to work as normal. The comatose person doesn’t carry out their usual voluntary actions, and certain abilities such as thinking are suppressed (per MedicalNewsToday). Although they’ve lost their higher-order brain capacities, such as awareness, cognition, and personality, many automatic functions and reflexes like breathing, swallowing, and circulation, continue to operate by themselves.
Spontaneous movements sometimes occur: The eyes may suddenly open as a reaction to noise, and some people have withdrawal responses to pain, while others can even be seen laughing or grimacing. This ultimately depends on the root cause of the incident and how it’s affected different components of the body. As the coma deepens, these responses can diminish or eventually stop entirely (via The New England Journal of Medicine). Some people in comas may need help breathing via a ventilator, according to the Brain Foundation. Almost every patient needs to be tube-fed and hydrated, which is usually done through IV injections.
What causes a coma?
A coma can be caused by a wide array of situations from medical to environmental (per MedicalNewsToday). Some people enter into a coma when the brain is deprived of oxygen, such as during a heart attack or stroke. It could be due to a brain injury brought about by a blow to the head, or a disease or illness that affects the central nervous system, like meningitis. Prolonged periods of skyrocketing or plummeting blood sugar levels can also precipitate a coma, while severe intoxication can lead to brain damage as a result of carbon monoxide poisoning. Its origins are varied and complex.
Most comatose patients are regarded as potentially salvageable depending on the cause, and provided that they’re properly cared for, according to a 2001 study published in the Journal of Neurology, Neurosurgery, and Psychiatry. Patients in a drug overdose coma tend to be in a pretty deep comatose state due to damaged brain stem reflexes. Comas triggered by a cerebrovascular disease, like a cerebral hemorrhage or a stroke, are said to have the worst prognosis of all.
What’s the difference between coma and sleep?
A coma can certainly look like a state of deep sleep. The person is unaware and unresponsive to what’s going on around them. Unlike being asleep, however, a comatose person can’t be awoken by external stimuli like sounds or sensations, and doctors and nurses are needed to help the patient stay alive (via The New England Journal of Medicine). While some people in a coma may be partially aware of their surroundings and those in a vegetative state can display some reflex and automatic behaviors, the brain isn’t working as if it’s in a deep slumber.
This also means it’s unlikely that normal dreams can occur. For instance, damage to the visual and auditory cortex means that visual dreams are lost, as are sounds and voices (via BBC Science Focus). An impaired reticular activating system — which regulates the body’s sleep-wake cycle — means that the comatose person can’t enter the phase of deep sleep known as rapid-eye-movement (REM), which facilitates dreaming.
The brain is in a similar state under anesthesia
The brain’s state in a coma might closely resemble the brain under anesthesia rather than a sleeping brain, according to some researchers. A 2010 review study published in The New England Journal of Medicine discovered that anesthesia influences the same regions of the brain that are affected when a person is in a coma: the thalamus, where consciousness is controlled; the cortex, which plays a key role in memory; the upper part of the mid-brain that’s involved in arousal and alertness, and the lower part of the brain stem, which controls breathing and heart rate.
Other studies point out that patterns of brain activity spotted in comatose patients are often similar to the type of activity observed in patients under general anesthesia. "General anesthesia is, in fact, a reversible drug-induced coma," researchers explained in a 2011 study published in The New England Journal of Medicine. "Nevertheless, anesthesiologists refer to it as ‘sleep’ to avoid disquieting patients."
The brain can still react to sounds
You may wonder just how much a person in a coma can hear and comprehend. Reports by those who’ve recovered from a comatose state suggest that some people can hear voices and even understand what’s being said to them (via BuzzFeed). Research tells us that the voices of loved ones recounting a familiar story can help arouse the unconscious brain and speed up recovery for the patient in a coma (via ScienceDaily).
A 2019 study from Frontiers of Young Minds used electroencephalography (EEG) to measure the neuronal activity of comatose patients as a way to determine how much they could actually hear. The researchers found that, even in a deep coma, the brain is capable of picking up on sounds, like approaching footsteps and bits and pieces of conversations. It appeared that several patients’ brains reacted to sounds that were presented as short rhythmic blips, and could even distinguish between the different sounds that were played to them. In fact, they displayed the same pattern of activity as healthy and awake brains. However, the capacity to tell different sounds apart diminished for patients who later passed away, according to the study authors, raising the question of "whether this decreased ability to tell sounds apart was related to the patient’s outcome."
Muscles waste away rapidly
A common problem facing many people in a coma is muscle wastage, also known as muscle atrophy (via Acta Informatica Medica). The comatose person is exposed to a long period of inactivity and sedation while they’re unconscious and immobile. During this time, they’ll experience immense muscle loss, as all muscles need to be used in order to function properly and maintain their strength. This means that many people typically feel extremely weak once they’ve recovered from a coma and have to strengthen and rebuild the muscles that rapidly faded away while they were bedridden.
Some people even have to learn to walk again after they come out of the hospital, while others can suffer long-term muscle damage (via CNN). Muscle wasting can have a lasting effect on other areas of the body as well, such as the cardiovascular, respiratory, and circulatory systems (per Acta Informatica Medica).
Some people experience strange hallucinations
Although dreaming is unlikely during a coma, other dream-like states and visions may be possible, according to some researchers (via Business Insider). If the myriad accounts of coma survivors are anything to go by, then strange hallucinations are pretty common. One reason for this is that people in intensive care are given a cocktail of medications, such as opiates, which can trigger intense or disturbing dreams that last for long periods of time (via Healthtalk).
Dreaming, nightmares, and hallucinations are generally common in the critically ill, and many patients experience distressing dreams despite having had no drugs. Research on dreaming during a coma is hard to conduct, as it’s tricky to investigate and understand what the brain goes through while it’s unconscious. It is also difficult to determine whether the mental states that people experience are actual dreams or mere hallucinations. What we know relies heavily on the memories and personal accounts of survivors, which can be hard for people to trace back and put into words.
How long will it take to wake up from a coma?
Physicians can find it difficult to specify exactly how long it will take for a person to come out of a coma. Comas can last from days to years, depending on the situation, according to the Brain Foundation. Furthermore, there’s no specific timeframe for the period of unconsciousness — it largely depends on the cause of the coma and the impact it has had on the brain. Recovery usually happens gradually, with a person becoming more alert over time. They may wake up for just a few minutes or hours each day until they’re able to stay conscious for longer periods of time. Some people transition into a vegetative or minimally conscious state, whereby they have limited awareness that drifts on and off.
While it’s rare, some comas have been known to last for several years. This can happen if the brain is profoundly damaged. A 2017 study published in the journal Current Biology described a patient who remained in a vegetative state for 15 years following a traumatic brain injury.
What is a medically-induced coma?
Despite sharing a similar name, a medically-induced coma is somewhat different from a traditional coma. Physicians can medically induce a coma using anesthetic drugs, such as propofol or a barbiturate, to shut down or minimize brain activity, putting the brain into temporary hibernation (via PLoS Computational Biology). Patients who are intentionally put into a coma are usually at high risk of brain injury due to a life-threatening illness, physical trauma, or drug overdose. The procedure reduces blood flow and slows down the brain’s metabolism in order to prevent swelling and inflammation, which can starve the brain of oxygen and cause permanent damage. A medically-induced coma gives the brain some time to rest and heal. The procedure is usually administered using an infusion pump, and the length of time that a patient is kept in the coma is largely dependent on the cause and severity of their condition.
Vagus nerve stimulation can improve recovery
The vagus nerve is the longest nerve in the body, which is known to regulate consciousness, awareness, sleep, and alertness (via MedicalNewsToday). It runs all the way from the bottom of the skull to the abdomen, connecting the brainstem to major organs in the body, such as the heart and gut. The role of vagal nerve stimulation in coma recovery is an important, albeit fairly new, discovery for researchers. In a 2017 study published in the journal Current Biology, a patient who had been in a vegetative state for 15 years following a car accident was able to regain some consciousness after his vagus nerve was continuously stimulated for a month. Neurosurgeons achieved this by fitting a vagus nerve stimulator into the man’s chest. The findings showed that daily vagal nerve stimulation led to notable improvements in the patient’s movements, attention, and brain activity. Unlike before, the man started responding to basic instructions. He could move his head and follow objects with his eyes, as well as stay awake for longer periods of time. The findings highlighted that vagus nerve stimulation — which is already used to treat a number of different conditions, including epilepsy and depression — has the potential to help restore a minimal level of consciousness, even in long-term coma patients (via MedicalNewsToday).