Human bodies know what time it is, even without the aid of a wristwatch. Every cell and every organ ticks and burbles according to our circadian rhythms. Recently, when researchers decided to look at the brain’s internal clock they discovered that all that biological activity stops at the moment of death, leaving a timestamp that may tell us the hour of a person’s passing.
People who died in the morning have a different mix of active genes and proteins in their brain cells than people who died in the evening or at night, reports Carl Zimmer for The New York Times. The discovery is more than just a morbid oddity. Researchers are trying to understand exactly how internal clocks dictate brain biology and chemistry. Figuring that out could help scientists treat sleep disorders, dementia, depression and more.
“Sleep and activity cycles are a very big part of psychiatric illnesses,” says Huda Akil, a neuroscientist based at the University of Michigan.
Akil and her colleagues have hunted through brains kept preserved at the University of California, Irvine, to find the signature that betrays the organs’ owners’ time of death. The team looked at the brains of 55 people who died suddenly, such as in a car crash, and analyzed the genes that were "turned on" at the time of death in six different brain regions involved in learning, memory, emotion and biological regulation.
They found more than 100 genes that ramp up their activity during certain times of the day. The genes include those that dictate metabolism, lipid synthesis and wakefulness. The researchers could even guess when the person died within an hour of their actual time of death.
Another study by a group at the University of Pittsburgh School of Medicine, inspired by Akil’s work, looked at 146 brains in their university collection. “Lo and behold, we got very nice rhythms,” Colleen A. McClung, the leader of the effort, tells the Times. “It really seems like a snapshot of where the brain was at the moment of death.”
McClung and her colleagues also looked at the patterns of genes turned on or off in the brains of young people and old people. They discovered that some of the genes with strong cycle patterns in young people had more subdued patterns in people older than 60. But other genes seem to became more active as people age. They reported their findings in Proceedings of the National Academy of Sciences last week.
Akil thinks that those changing patterns might mean that one clock winds down as we age and another might start up to compensate. How well the brain is able to keep time might determine whether a person experiences age-related neurodegeneration.