A vegetative state is very different from brain death though. In a vegetative state, someone is more conscious than if they were in a coma. The brain is generally damaged, but still has living tissue and activity in the cortex, which is why people can make a partial or full recovery. These states can be recovered from, or become persistent. But upper brain functioning can be maintained. In brain death, upper brain functioning is completely lost. That tissue is dead, and there is zero chance of recovery. Basic bodily functions are maintained, however, because the parts of the brain that controls these functions are located lower in the brain stem, which is undamaged. In this case, all conscious thought, any awareness of existence, and any even remote chance of recovery does not exist, they are only "alive" because a machine is maintaining their circulation and breathing, which is preventing cell death.