> so are you saying you can go down but not up You have a specific amount of neurons and a lot of them die every day. The body doesn't produce them like other

> so are you saying you can go down but not up You have a specific amount of neurons and a lot of them die every day. The body doesn't produce them like other cells after a certain age threshold (age 21 IIRC, also depends on the individual). - Although this theory is currently on the edge of being disproved, it's clear that adult brains are not producing many of them. Training and experience can compensate this loss, but the general cognitive capacity gets reduced each day. Pretty depressive to think about it, but maybe we'll be able to use stem cell research to change this in the future. edit: I don't want to state this as definitive facts. The field of neurogenesis is currently heavily researched and there are some hints that adult brains might be able to produce new neurons. See https://www.scientificamerican.com/article/does-the-adult-brain-really-grow-new-neurons/ https://www.scientificamerican.com/article/does-the-adult-br... for a discussion. What I think is most likely is that we lose 10x times the amount of neurons that we create each day, so even if it's producing new ones, the rate of death is higher.