According to new research from Oregon Health & Science University, injuries and diseases that afflict a relatively small number of brain cells create a chain reaction that stops activity across a complex network of neural circuits. Scientists believe the findings can shed light on why people can suffer from temporary but severe loss of cognitive function after suffering a traumatic brain injury or contracting a disease.

According to Marc Freeman, Ph.D., the director of the Vollum Institute at OHSU, “Even the so-called bystander neurons that aren’t injured or diseased can sense there’s been an injury and radically change their function. That means that it’s not just the broken neurons that are affected when you have a nervous system injury, it’s maybe all of the neurons.”

The discovery was made by researchers while they were working with the fruit fly Drosophila, which is a well-established model for neural networks in people. Researchers focused their attention on the axon, a threadlike portion of a nerve cell that transmits signals around the nervous system. To recreate the damage that occurs from a minor head injury, researchers snipped a small number of axons from a larger bundle.

Researchers discovered that the impact of the relatively small injury spread beyond the cut axon and suppressed sensory signals among neurons that weren’t initially damaged. According to the study, the response is attributed to glial cells, which are supporting cells within the brain.

Speaking about the findings, Dr. Freeman said “Glial cells are the watchdogs of nervous system health. Our work suggests that even when there’s a relatively small injury to some neurons, they can run out like Paul Revere and shut everything down.” Freeman’s working theory is that this bystander effect can evolve to help to conserve energy in large swaths of the nervous system following disease or injury. Dr. Freeman theorizes the bystander neurons can effectively revive once it becomes clear that they are uninjured.

“Our best guess is that it allows the nervous system to pause after an injury. It enables cells to assess their status and, if they’re not healthy, activate programs to destroy themselves. If they’re healthy, they recover,” said Dr. Freeman.

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