Today, where a definition of the moment of death is required, doctors usually turn to the concept of brain death which considers people to be dead when the electrical activity in their brain ceases permanently. Once brain death occurs, it is not believed possible to return to life. The determination of the exact moment of death is important in determining when resuscitation efforts should end and when organ transplants are allowed; this is highly contraversal in some infant diseases such as anencephaly, in which there is no higher brain present.
It is presumed that a permanent stoppage of electrical activity indicates the end of consciousness. Those that view that only the neo-cortex of the brain is necessary for consciousness, however, sometimes argue that only electrical activity there should be considered when defining death. In many cases, especially when elevated intracranial pressure prevents blood flow into the skull, the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex.
In most places the more conservative definition of death (cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted (for example the Uniform Definition of Death Act in the United States). Protocols for determining brain death generally require two EEGs showing no electrical activity, taken 24 hours apart. The absence of brain activity (including brain stem activity) necessarily implies that the patient is incapable of maintaining heartbeat or breathing unassisted by a respirator; and that cerebral reflexes are absent.