For decades, neuroscientists have taught that neurons do not regenerate once they are damaged or destroyed. This belief has shaped how brain injuries are understood and treated. Yet people often regain at least some lost abilities after trauma, raising an important question: if neurons do not grow back, how does recovery happen?
A new JNeurosci paper offers insight into this puzzle. Athanasios Alexandris and colleagues at Johns Hopkins University used mice to study what happens inside the visual system after traumatic brain injury. The visual system includes cells in the eye that send information to the brain, allowing animals and humans to see. Damage to this system can disrupt communication between the eye and the brain, leading to vision problems.
After injury, the researchers closely tracked the connections between cells in the eye and neurons in the brain. Instead of finding widespread regrowth of new cells, they observed something different. The cells that survived the injury began to adapt.
These surviving cells grew extra branches, which allowed them to connect with more neurons in the brain than before. This process, known as sprouting, helped compensate for cells that were lost due to injury. Over time, the number of connections between the eye and the brain returned to levels similar to those seen before the injury occurred.
Importantly, these rebuilt connections were not just structural. Measurements of brain activity showed that the new pathways were working properly and could transmit signals effectively. In practical terms, this means the visual system was able to function again despite the damage.
The study also revealed a significant difference between male and female mice. While male mice showed strong recovery through this compensatory sprouting process, female mice experienced slower or incomplete repair. The eye to brain connections in females did not always fully return to preinjury levels.
According to the authors, these findings point to a recovery mechanism that operates differently depending on sex. As Alexandris explains, "We didn't expect to see sex differences, but this aligns with clinical observations in humans. Women experience more lingering symptoms from concussion or brain injury than men. Understanding the mechanism behind the branch sprouting we observed -- and what delays or prevents this mechanism in females -- could eventually point toward strategies to promote recovery from traumatic or other forms of neural injury."
The research team plans to continue investigating why this repair process differs between females and males. By uncovering the biological factors that influence neural recovery, they hope to identify new ways to improve healing after brain injuries, including concussions and other forms of trauma.
