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The Three States Of Unresponsiveness: Sleep, Anesthesia, And Coma

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If a person needs to receive anesthesia in order to undergo surgery, they may hear the doctor saying ‘We are going to put you to sleep’. Is this person really going to sleep while being operated on? And how about people who are in a coma – are they just sleeping for a very long time?

In recent years, there has been a rising interest among the general public on the similarities and differences when it comes to sleep, anesthesia, and coma. They are definitely not the same. There are different reasons for being in any of those states, the brain activity is different, the level of (un)responsiveness to the outside world as well as physical characteristics are to a greater or lesser extent, different.

Here we will compare sleep to anesthesia and coma, and provide additional details about each of the three.

The distinct aspects of sleep, anesthesia, and coma


Sleep is a naturally occurring state of altered consciousness. It normally happens every night and lasts for about 7-8 hours (for most people). During sleep, we are more or less responsive to our surroundings, depending on the sleep stage.

Every night, our brain cycles through four sleep stages – three NREM (non-rapid eye movement) and one REM (rapid eye movement) stage. Two NREM stages are classified as light sleep, whereas the third one is called deep or slow-wave sleep – and this is when we are the least responsive to the outside world. Even so, we can be woken up by a loud noise, shaking, or pain. REM stage is the most famous one because that’s when we have the most vivid dreams.

Dreams are not the only thing that characterizes sleep. Our brains consolidate memory (strengthen memories that we are going to remember and weaken those we’re about to forget), and release the human growth hormone (which repairs our tissues and cells). Our bodies rest and we regain the energy we’d lost the previous day.

Without sufficient sleep, humans start making mistakes, their immune system drops, many body processes are impaired (both physiological and psychological), such as hormonal imbalances, moodiness, and forgetfulness. It is speculated that people could even die from a lack of sleep.

The world-famous singer Michael Jackson died after being given propofol (a sedative used for anesthesia) for 60 days straight. Although he was seemingly asleep every night, he didn’t have any REM sleep and his NREM sleep was severely impaired. A study has shown that patients receiving propofol don’t show signs of having either REM sleep or a normal sleep cycle.


General anesthesia is given by doctors to their patients in order to make them unaware of pain and trauma before certain types of surgery. Anesthesia can also be administered locally, that is, in small areas (for example, for tooth surgery) or regionally, say, in entire limbs (arm or leg surgery) but in both cases, the patient stays awake and pain-free.

General anesthesia is a mix of drugs which get us into a state similar to a coma in terms of unresponsiveness, however, humans get out of it almost as soon as the drugs stop being administered intravenously (IV). Healthy, young people are usually safe to receive anesthesia, whereas the obese, the elderly, and smokers run the risk of having some of the numerous possible complications and side effects. Common side effects of general anesthesia include nausea, confusion, problems with mouth and throat (soreness, dryness, hoarse voice), pain in muscles, shivering, and sleepiness.


Coma is a state in which a person is unconscious for a long time, completely unresponsive to the outside stimuli, like sounds and pain.

In most cases, coma is a consequence of head trauma or brain problems (swelling, bleeding, stroke, accumulated toxins, repeated seizures). Other possible triggers of coma are extremely low blood sugar level, oxygen restriction (after a cardiac arrest or drowning, for example) and infection.

There are several types of coma. Some of them are reversible, which means that a patient can become conscious again, whereas some are so severe that people will most likely stay in a comatose state until physical death.

Toxic-metabolic encephalopathy is a type of coma caused by various illnesses which lead to brain dysfunction and in most cases, it can be reversed. Anoxic brain injury happens after oxygen deprivation which kills off brain cells and tissues.

Persistent vegetative state is a state in which a person can’t move voluntarily and may have limited consciousness or apparent wakefulness through some spontaneous body movements. There is a small chance of a person regaining higher brain functions in the first three months of the brain injury. A person in a vegetative state may be completely unconscious, although brain still keeps the heart and other vital organs working and alive, which makes this state different from someone who is brain dead. When someone is brain dead, they are declared clinically and legally dead. It’s when all brain functions cease irreversibly.

Medically-induced coma. We might even call it prolonged anesthesia because a person receives anesthetics over a period of time in order to stay unconscious and prevent the swelling in the brain. As soon as doctors decide it is safe for the person to regain consciousness, they stop giving them drugs and shortly after, they emerge from this state.

Finally, there’s a rare condition called locked-in syndrome. It’s different from the vegetative state in that the patient is fully aware and has a completely normal brain functioning, however, is unable to move the entire body – except for the eye muscles.

EEG scan showing brain activity during sleep
Figure 1 Electroencephalographic (EEG) Patterns during the Awake State, General Anesthesia, and Sleep (words in parenthesis denote what state the given brainwaves are similar to). EEG taken from Watson et al.

Sleep and Anesthesia

The main difference between sleep and anesthesia is that sleep occurs naturally whereas anesthesia happens only if certain drugs are administered. Those drugs make people unconscious by ‘breaking’ nerve circuits that make us conscious. When under anesthesia, our brain experiences a stalemate in information flow – but during sleep, our mental activity is high as our brains replenish neurotransmitters which send out information and help not only with memory but also with the cleanup of certain chemicals which built up in nerve cells during wakefulness.

Sleep and Coma

Coma is a state in which a person wouldn’t be able to survive for a long time without help from doctors and nurses. Although some people can be partially aware while in a coma, it is a state in which the brain is not working properly – and a person can’t be ‘woken up’ from a coma like they can from sleep. A person in a coma can dream, however, it very much depends which part of the brain is damaged. Damage in visual cortex can result in loss of visual dreams, and the same goes for auditory cortex. If the damage is localized in the part of the brain that controls the states of sleep and wakefulness, dreams might be highly unlikely.

Coma and Anesthesia

Although one type of coma (medically-induced) is triggered on purpose via anesthetic drugs, just like the general anesthesia, we will focus here on other coma types. Anesthesia is a temporary state which usually lasts almost as long as the surgery itself (or slightly longer), whereas coma is caused by brain damage and lasts for a longer amount of time. Doctors usually can’t tell whether someone will recover from a coma or not. Even though some comatose patients can regain consciousness, the percentage is very small. After anesthesia, every patient regains full consciousness (unless after an extremely rare complication where a person doesn’t wake up). Doctors know well who the risk groups for anesthesia are and do not take big risks. Some comatose patients can experience dreams, however, none of the patients who receive anesthesia has any dreams or memory of what happened (again, in extremely rare cases, a person can stay fully aware of everything during surgery and feel all the pain).

Additional resources

  1. Kondili E, Alexopoulou C, et al. Effects of propofol on sleep quality in mechanically ventilated critically ill patients: a physiological study. Intensive Care Medicine. https://www.ncbi.nlm.nih.gov/pubmed/22752356 Accessed January 27, 2019.
  2. Watson C, Bagdoyan H, Lydic R. A neurochemical perspective on states of consciousness. In: Hudetz AG, Pearce RA, editors. Suppressing the mind: anesthetic modulation of memory and consciousness. New York: Springer/Humana Press; 2010. pp. 33–80.
  3. Brown E. N, Lydic R, Schiff N. D. General Anesthesia, Sleep, and Coma. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3162622/ Accessed January 27, 2019.
  4. Edlund, M. J. Comas Don’t Count as Sleep. Psychology Today. October 13, 2011. https://www.psychologytoday.com/us/blog/the-power-rest/201110/comas-dont-count-sleep Accessed January 27, 2019.

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.

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