What happens to the body and brain in a coma?

A patient lying unconscious and in a state of coma in the hospitals emergency department

While a body in a coma may look all calm, docile, and irresponsive, there is a lot going on underneath the surface. For most people, it is scary yielding to their body as it shuts down using all available energy for healing and leaving no room for the luxury of consciousness.

During a coma, the body looks healthy but appears to be in a state of deep sleep. A person in a coma does not have an awareness of the surroundings and can not think consciously; however, the person’s body still supports essential life functions like blood circulation and breathing.

Also, a person can exhibit some slight body movement during a coma, such as grimacing or eye-opening. However, the person is unaware of those movements and does not have control over them.

Suppose you are drunk to a stupor but can be awakened with some effort; you are not in a coma because a person in a coma can not be awakened even if a loudspeaker is placed over them.

Note that clinicians can medically induce a coma in a patient to rest the brain and avoid further brain damage.

Even though coma is a common clinical presentation in hospital emergency departments (ED), there is a sparse comprehensive research on its global prevalence. Also, surprisingly, the number of published studies of patients with coma is small.

Before going deep into what happens during a coma, you must understand what a coma is. Some people say a coma is a state of deep sleep. But is coma a form of sleep?  

What is a coma

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A coma is when the body is in a deep state of unconsciousness caused by trauma to the brain, toxins, infections like meningitis or an underlying health condition such as diabetes and cardiac disease. The brain is always affected irrespective of the cause of a coma.

There are various forms of coma such as:

  • Catatonia: Where the coma patient shows no movement or response of any kind
  • Vegetative coma: A prolonged state of unconsciousness in which the body occasional makes slight movements like yawning or grunting sounds but still does not respond to stimuli
  • Brain death: The brain is damaged and its functions destroyed, but somehow autonomic functions continue.

The word “coma” emerged around the 17th century and is derived from the Greek word for “deep sleep”. A coma is different from sleep because people in a coma can not consciously respond to any form of stimuli. They cannot be aroused.

What happens to the brain during a coma

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During a coma, there is little or no brain activity. Also, what happens in the brain during a coma depends on the specific cause of the coma. 

Comas caused by metabolic, toxic or infectious agents occur due to impairment in the delivery of oxygen and impaired substrate delivery. This, in turn, interferes with neuronal excitability and cerebral metabolism.

Maintaining a state of consciousness requires that certain areas of the brain (the cerebral hemispheres and the reticular activating system, RAS) function properly.

In order to understand what happens to the brain during a coma, it is important to understand how these two brain parts that control consciousness function.

The cerebral hemispheres constitute the largest part of the brain (called the cerebrum). They are the areas of the brain you see when the scalp is removed. They extend from the front of the head to the back. They are divided into left and right by a fissure that runs through the middle.

The cerebral hemispheres control speech, hearing, thought, memory, language, perceptual awareness, sense of touch, vision and personality development. One distinct thing about the two hemispheres is that one side controls the other side of the body, i.e., the right cerebral hemisphere controls the left side of the body and vice versa. 

Research has shown that stimulating one side of the brain sends electrical signals to the other part of the body. This means if the left side of the brain that controls arm movement is damaged, the right arm may become paralyzed or weak. 

However, both the left and right cerebral hemispheres are affected during a coma. Damage to one side of the brain may cause severe neurological complications, but it is not enough to induce a coma.

The reticular activating system (RAS) is a network of neurons that play important roles in inducing and maintaining awareness. 

During a coma, consciousness is turned off by an interference with the RAS, which controls cognitive consciousness. This means that direct damage of the RAS can alter alertness.

Is the body affected during a coma?

The brain is the main part of the body affected during a coma. The rest of the body seems not to be that much affected. However, since the brain controls body activities like movement, a person in a state of coma may be unable to move even a finger.

Also, during a coma, the part of the brain that controls higher consciousness is impaired. However, the part that helps the body carry out basic functions like a heart beating, breathing and digestion might continue to function. Hence, the body cells can get the nutrients and oxygen essential for survival. 

Patients in coma are typically hydrated and fed by giving them injections and drips through their veins. They may also need the help of an artificial breathing apparatus to breathe. 

What happens when you wake up from a coma

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Waking from a coma is usually a gradual process. People who are waking from a coma often start reacting to certain stimuli. Consciousness is fully regained only when perceptivity and reactivity are back to normal.

In some cases, a patient recovering from a coma will have to relearn some areas of perceptivity, such as using the bathroom, speaking or bathing. A patient's recovery progress is measured by how the patient responds to external stimuli.

Some things people experience when they wake up from a coma include:

  • Post-coma unresponsiveness (eye movement with no other signs of consciousness)
  • Minimal consciousness (regained state of awareness)
  • Post-traumatic amnesia (loss of memory following trauma)
  • Agitation 
  • Confusion
  • Disabilities caused by brain damage

Another common issue that patients who recover from coma face is muscle atrophy. Muscle atrophy is the loss or wasting (thinning) of muscle tissues. It is caused by prolonged inactivity (when the muscles are not used for long).

Showing empathy to patients recovering from a coma can help their recovery journey. Recovering patients might lose their own empathy skills due to brain damage. However, you should be patient with them and help them recover better.


  1. Forsberg, Sune et al. (2012). Prognosis in patients presenting with non-traumatic coma.  
  2. Maiesse, Kenneth. (2020). Overview of coma and impaired consciousness.
  3. Tsao, Hoi. (2006). What happens during a coma?  
  4. Young, Brian. (2020). Stupor and coma in adults.