A person who endures a severe traumatic brain injury or other serious situations such as heart failure or near drowning, will sometimes fall into a persistent vegetative state. The persistent vegetative state is a disorder of consciousness in which the patient is awake, but unaware or unconscious. This occurs as a result of damage to neurons in higher-level areas of the brain, which are important for learning, memory, and self-awareness. Neurons in the brain-stem, which is important for basic functions such as heart rate and respiration, however, will remain intact in people in a persistent vegetative state.
A recent animal study investigated the factors that made brain-stem neurons less vulnerable to injury than neurons in higher-level areas of the brain. Using high powered imaging and recording techniques, the researchers found that neurons in the brain-stem were resistant to a certain physiological response to injury that caused swelling and cell death in other areas of the brain. This resistance preserved brain-stem functioning while other parts of the brain continued to degenerate. The researchers suggest that this mechanism may be responsible for the characteristic condition of "awake but unaware" in the persistent vegetative state.
Brisson CD, Hseih YT, Kim D, et al. Brain-stem neurons survive the identical ischemic stress that kills higher neurons: Insight to the persistent vegetative state. PLoS One. (May 2014).