How Comas Work

Doctors often use MRI scans to check the brain tissue damage of a comatose patient.
© Carlos Torres

In December 1999, a nurse was straightening the bed sheets of a patient when she suddenly sat up and exclaimed, "Don't do that!" Although this may not sound unusual, it was pretty surprising to her friends and family -- Patricia White Bull had been in a deep coma for 16 years. Doctors told them that she would never emerge from it.

How can a comatose person emerge after so long? What causes people to fall into comas in the first place? What's the difference between being in a coma and being in a vegetative state? There are a lot of misconceptions and confusion about the state of unconsciousness known as a coma. In this article, you'll learn the physiological processes that trigger a coma, how a real-life coma differs from television depictions and how often people awaken after months or even years of being in a coma.


The word coma comes from the Greek word koma, which means "state of sleep." But being in a coma is not the same as being asleep. You can awaken someone who is asleep by talking to them or touching them. The same is not true for a comatose person -- he is alive and breathing, but so unconscious that he can't respond to any stimuli (such as pain or the sound of a voice) or perform any voluntary actions. The brain is still functioning, but at its most basic level. To understand this, we first need to review the parts of the brain and how they work.