Near-death experiences are often followed by assertions of a kind of consciousness after the heart stops, and it is possible that science may begin corroborating elements of those stories. What follows is a small sampling of studies that suggest postmortem brain activity allows the deceased to be aware that they are dead.
A 2014 study, led by Dr. Sam Parnia (director of critical care and resuscitation research at NYU Langone School of Medicine), examined people who had suffered cardiac arrest and been declared dead:
A significant number of participants in the study report being aware of their surroundings during the period in which they were pronounced dead. Though most were unable to recall specific memories, 39 percent of the study’s participants could describe “a perception of awareness.” A small percent say they were also able to hear full conversations, even see things happening around them. Lest you think these accounts a hoax, medical professionals and staff who were present at the patient’s time of death were also able to verify these stories.
In 2013, researchers at the University of Michigan studied the brains of anesthetized rats that subsequently experienced heart attacks, documenting brain activity which suggested a "hyper-alert state" just after death:
“This is a very neat demonstration of an idea that's been around for a long time: that under certain unfamiliar and confusing circumstances — like near-death — the brain becomes overstimulated and hyperexcited,” Jason Braithwaite, professor at the University of Birmingham, told BBC in regards to the rat research. “Like ‘fire raging through the brain’, activity can surge through brain areas involved in conscious experience, furnishing all resultant perceptions with realer-than-real feelings and emotions.”