Even after we die, some of our brain cells can experience one last and large momentary burst of life, new research out Tuesday suggests. The study found evidence that certain “zombie genes” in our brain cells are active more frequently soon after death, which causes some cells to immensely expand for hours. The findings won’t radically change our concepts of life and death, but they may hold some important implications for studying brain tissue taken post-mortem.
It’s no secret that our cells can stay alive and function for a while even after we’re clinically dead, before finally flickering out. But though nearly every cell carries the same genetic information as the next, different types of cells express this genetic information differently, with various genes being turned on or off. And when the researchers looked at the gene expression of different cells inside a “dying brain,” they found some distinct patterns.
For their study, published in Scientific Reports on Tuesday, the team looked at samples of brain tissue donated by patients who had recently undergone brain surgery for epilepsy (surgical treatments can safely remove parts of the brain involved in the seizure disorder). They then mimicked the process of brain death by leaving out the freshly removed samples at room temperature for various periods of time, for up to 24 hours. All the while, the team was collecting information on the cellular and genetic activity of these cells.
In a majority of the genes they studied, characterized as “housekeeping genes” that maintain basic cellular function, they found that the genes remained at the same level of activity for the entire 24 hour period. In the “neuronal” genes, genes that are turned on in the neuron cells responsible for brain functions like thought and memory, their activity started to drop after 12 hours.
But in a third group of genes, linked to the function of glial cells—the immune and support system of the brain—gene expression actually spiked after “death” and continued to increase up to 24 hours later. The glial cells themselves also expanded massively in size and even grew new “arms,” at the same time as the neurons in these samples were degenerating.
The results don’t prove that zombies are theoretically possible, and it’s not even really a huge surprise that glial cells are especially active post-death. The cells are likely responding to the injury and inflammation that’s going on in the brain when it’s deprived of oxygen after someone’s final moments. But the findings do present a potential wrinkle for how a lot of human brain research is conducted, according to the authors, since many studies rely on post-mortem examinations of the brain.
“Most studies assume that everything in the brain stops when the heart stops beating, but this is not so,” said study author Jeffrey Loeb, head of neurology and rehabilitation at the University of Illinois at Chicago College of Medicine, in a statement released by the university. “Our findings will be needed to interpret research on human brain tissues. We just haven’t quantified these changes until now.”
One problem is that research into disorders like Alzheimer’s disease and other forms of dementia is often dependent on post-mortem brain samples that are collected 12 or more hours after death. If the findings here are valid, then many of these studies might be missing important clues left inside dying cells that could go missing later. Loeb and his team hope studies going forward can better account for the changes that take place in a dying brain. A potential solution, for instance, might be to collect brain samples for research even sooner post-mortem or to rely more heavily on samples from willing patients who are getting brain surgery anyway.
“The good news from our findings is that we now know which genes and cell types are stable, which degrade, and which increase over time so that results from postmortem brain studies can be better understood,” Loeb said.