Almost all human cells reproduce on a cycle. 

Up to ten percent of your heart is replaced each year. Red blood cells are replaced every four months, skin cells every two weeks. 

But neurons, the cells that make up the brain and spinal cord, don't regenerate. 

It turns out that under the right conditions, neurons can recover. If they can break from normal operations and focus on healing, they have a chance at regrowth. 

It's human nature to wanna fix what's broken. 

We may not be able to exactly replicate what we lost, but in its place, we'll grow something new. It's a long process, but it happens. Slowly but surely. 

Until we have what we need.