braindeath and it's cognitive significance

Every Human being always tried to define death in order to reach a solution to live, maybe forever. He always faced with such questions: what is death? When we can say somebody died? We have two main approaches in medicine to define death: Cardiopulmonary death which means the irreversible cessation of cardiopulmonary system (heart and lungs) and brain death which means the irreversible cessation of brain functions. The second approach promoted by the way of using ventilators which could revive brain death Patients. So brain functions became the most important criterion to define death. Now the question is: if the irreversible cessation of cognitive activities in brain is the criterion to define death or the irreversible cessation of cardiopulmonary system? And if we choose the first, which property or function can be the criterion to define cognitive activity? In this essay we conclude that the irreversible cessation of cognitive activities in brain is the criterion to define death and we try to reason that awareness is the right criterion to define cognitive activity.