"The mind is the result of neural activity, which ceases at brain death due to the massive premature death (necrosis) of cerebral neurons. In the process of clinical death, the heart stops working and pumping blood to the brain, thereby cutting the brain's essential supply of oxygen and of other less urgent nutrients. Measurable brain activity stops within 20 to 40 seconds. As characteristic of all biological cells, nerve cells die once deprived of oxygenated blood, destroying the brain."
"No feature of consciousness has ever been discovered that does not depend 100% on neurophysiology. Stimulate the brain with chemicals or an electrical current, and the person's experience changes; let a person's experience vary, and you can measure the changes in chemistry or electrophysiology. When a brain is damaged, the person’s mental life is diminished accordingly, and when the brain's activity ceases, the mind goes out of existence."
"The supposedly immaterial soul, we now know, can be bisected with a knife, altered by chemicals, started or stopped by electricity, and extinguished by a sharp blow or by insufficient oxygen."
"In brain death there is irreversible cessation of all functions of the brain including the brainstem. Consciousness is, therefore, permanently lost in brain death." - The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology
"Consciousness is the result of matter/particles being in specific, highly specialized arrangements. When particles cease to be in those arrangements, consciousness ceases to be."
"In intelligent animals, human and non-human alike, consciousness as we know it begins to appear at neonatal stages, is lost and recovered sporadically in the course of their lifespan—during deep sleep, syncope and sometimes coma, as lack of communication between neurons—and is lost permanently once their brains are dead. Before the mind begins to form, the organism's consciousness does not exist, but is absent in the very same manner as it is after it dies."