Scientists Didn't Expect This Body Part To Come To Life After Death

New research has thrown the definition of death into question. According to the United State's Uniform Determination of Death Act of 1981, death is defined as either the "irreversible cessation of circulatory and respiratory functions" or the "irreversible cessation of all functions of the entire brain, including the brain stem" — whichever comes first. That legal definition has been used since it was first released in the 1980s, but a 2021 study published in the journal Scientific Reports suggests that the "cessation" of brain function after death isn't so cut and dry.

By analyzing the removed brain tissue of patients who underwent brain surgery, the team discovered that a specific group of brain cells continues "living" after their connections to the rest of the brain are severed. The researchers state that certain cells can remain active for many hours after death. And these "zombie cells" don't just keep living. Instead, their gene activity actually increases in response to the death of the surrounding neurons, swelling them to massive sizes. Their gene activity peaks around 12 hours after death and then dies down.

The so-called "zombie cells" are known to scientists as glial cells, and they're critical components of the brain's complex anatomy. Glial cells don't contain the memories, emotions, and thoughts of a person like neurons do. In fact, neurons are usually the first cells in the brain to die. Instead, glial cells provide structural support to the nervous system and protect neurons. They also help the brain heal when it's injured by inflaming to larger sizes to flood the damaged site with white blood cells. After death, glial cells go through the same inflammatory response as they would following a concussion or stressing over an imminent exam.

Following discoveries surrounding "brain death," a push for a revision to the Uniform Determination of Death Act began to gain steam in the early 2020s. Proponents of a revision pointed to the many inconsistencies surrounding the legal definition of what death is and how to test it. It appeared that the Uniform Law Commission (ULC) responsible for the Act considered changing it, but in 2023, the ULC decided to suspend its efforts and stuck with the original definition. 

While the legal definition of death may be written in stone, death has different meanings to different people. After all, the cells in the body's largest organ, the skin, continue reproducing after the heart and brain stop functioning, sometimes for weeks. Should we define death as the moment the last cell dies, or when the last memories die? Do we even need to say? The entire inquiry can get philosophically messy, and indeed it did when the Commission first deliberated over the definition in 1980. During the original deliberation, the Commission listened to numerous testimonies from individuals from all walks of life.

After considering numerous religious, medical, philosophical, and biological definitions of death, the ULC decided that "total brain death" was a definition "sufficient to determine death of the organism." On the one hand, the definition lacks nuance. On the other, it is true that the parts of the brain that make you who you are — the neurons and their emergent networks — die hours before the inflammatory glial cells reach their peak of activity. Perhaps the Commission's decision to maintain its 45-year-old definition of death is just a convenient way of saying, "Who knows?"