death and life
Main article: Medical definition of death Symbols of death in a painting: it shows a flower, a skull and an hourglass A flower, a skull and an hourglass stand for life, death and time in this 17th-century painting by Philippe de Champaigne Ivory pendant of a Monk's face. The left half of the pendant appears skeletal, while the right half appears living French – 16th-/17th-century ivory pendant, Monk and Death, recalling mortality and the certainty of death (Walters Art Museum) The concept of death is a key to human understanding of the phenomenon. There are many scientific approaches to the concept. For example, brain death, as practiced in medical science, defines death as a point in time at which brain activity ceases. One of the challenges in defining death is in distinguishing it from life. As a point in time, death would seem to refer to the moment at which life ends.
Determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems. Such determination therefore requires drawing precise conceptual boundaries between life and death. This is difficult, due to there being little consensus on how to define life.
This general problem applies to the particular challenge of defining death in the context of medicine. It is possible to define life in terms of consciousness. When consciousness ceases, a living organism can be said to have died. One of the flaws in this approach is that there are many organisms which are alive but probably not conscious (for example, single-celled organisms). Another problem is in defining consciousness, which has many different definitions given by modern scientists, psychologists and philosophers. Additionally, many religious traditions, including Abrahamic and Dharmic traditions, hold that death does not (or may not) entail the end of consciousness. In certain cultures, death is more of a process than a single event. It implies a slow shift from one spiritual state to another.
 Other definitions for death focus on the character of cessation of something.[clarification needed] More specifically, death occurs when a living entity experiences irreversible cessation of all functioning. As it pertains to human life, death is an irreversible process where someone loses their existence as a person. Historically, attempts to define the exact moment of a human's death have been subjective, or imprecise. Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted. Events which were causally linked to death in the past no longer kill in all circumstances; without a functioning heart or lungs, life can sometimes be sustained with a combination of life support devices, organ transplants and artificial pacemakers. Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death" to define a person as being dead; people are considered dead when the electrical activity in their brain ceases.
It is presumed that an end of electrical activity indicates the end of consciousness. Suspension of consciousness must be permanent, and not transient, as occurs during certain sleep stages, and especially a coma. In the case of sleep, EEGs can easily tell the difference. The category of "brain death" is seen as problematic by some scholars. For instance, Dr. Franklin Miller, senior faculty member at the Department of Bioethics, National Institutes of Health, notes: "By the late 1990s... the equation of brain death with death of the human being was increasingly challenged by scholars, based on evidence regarding the array of biological functioning displayed by patients correctly diagnosed as having this condition who were maintained on mechanical ventilation for substantial periods of time. These patients maintained the ability to sustain circulation and respiration, control temperature, excrete wastes, heal wounds, fight infections and, most dramatically, to gestate fetuses (in the case of pregnant "brain-dead" women)." Those people maintaining that only the neo-cortex of the brain is necessary for consciousness sometimes argue that only electrical activity should be considered when defining death. Eventually it is possible that the criterion for death will be the permanent and irreversible loss of cognitive function, as evidenced by the death of the cerebral cortex.
All hope of recovering human thought and personality is then gone given current and foreseeable medical technology. At present, in most places the more conservative definition of death – irreversible cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex – has been adopted (for example the Uniform Determination Of Death Act in the United States). In 2005, the Terri Schiavo case brought the question of brain death and artificial sustenance to the front of American politics. Even by whole-brain criteria, the determination of brain death can be complicated. EEGs can detect spurious electrical impulses, while certain drugs, hypoglycemia, hypoxia, or hypothermia can suppress or even stop brain activity on a temporary basis. Because of this, hospitals have protocols for determining brain death involving EEGs at widely separated intervals under defined conditions.