According to Johns Hopkins Medicine, the definitions of each condition are as follows: Brain death. Also called death by neurological criteria, brain death is an irreversible cessation of all functions of the entire brain, including the brain stem. A person who is brain dead is dead, with no chance of revival. A state of profound unresponsiveness as a result of severe illness or brain injury. Patients in a coma do not open their eyes or speak, and they do not exhibit purposeful behaviors. Some patients need ventilators while others do not. Doctors sometimes place patients in medically induced comas to give their brains time to heal. In general, comas last just a few days or weeks. Patients either die or regain consciousness, or in some cases progress to a vegetative state. Vegetative state. The person has depressed consciousness, brain stem function and can breathe without support. Patients in a vegetative state may respond to pain or loud sounds, go through sleep-wake cycles, and exhibit involuntary motions. A person in a vegetative state for more than a year is considered to be in a permanent vegetative state with extremely low chance of recovery. Perhaps the most crucial difference between a coma/vegetative state and brain death is that when someone is in a coma or vegetative state, there is still the possibility of the patient regaining consciousness. In a brain dead person, there is no possibility of consciousness returning to the patient.