Though the science behind comas is greatly disputed, there are some things we know for certain. The word coma comes from the Greek term for a state of sleep and refers to when your body is impaired from conscious action. When a person is in a coma, they are alive and can sometimes even breathe on their own, but will not be able to respond to stimuli like light, sound, or touch. While the brain of a comatose person is active at a base level, you certainly aren't doing much thinking when you're in a coma.
A coma usually is caused when blood flow and therefore oxygen is cut off from the brain, but keep in mind that every coma is different and impacts each patient uniquely. Following the Glasgow Coma Scale, which assigns a ranking from 3-15, the lower your scale, the worse off you are. On average, comas last from 2-4 weeks, but it is generally true that the longer a person is comatose, the less of a chance of surviving he or she has. Unfortunately, there is no cure to waken a patient from a coma.
There's a lot of debate about the brain activity of comatose patients and what is or is not going on in people's brains when they are in a coma. To learn more about some of the studies that have been done on this topic, watch the video!