The brain can make new neurons throughout your life. For a long time it was accepted that you’re born with all the neurons you’ll ever have, but that’s not true. New neurons form mostly in the hippocampus, olfactory bulb, subventricular zone, and possibly in the cerebral cortex.
But all is not rosy with getting new brain cells. It turns out that new neurons in the hippocampus, the main part of the brain associated with memory, disrupt older memories. While the new neurons make it easier to learn new things, they make it harder to remember older things already known.