When new neurons are born from stem cells within the brain, which can then form new circuits. Neurogenesis surprisingly only happens in a few areas in the brain. One area is the hippocampus which needs a lot of new neurons because it encodes new memories. Another area is the olfactory bulb, which allows us to sense smells.

Contrast this with the prefrontal cortex. Sitting at the front of your brain, the prefrontal cortex is what performs high level abstraction and ‘smart’ thinking. Interestingly, the prefrontal cortex is not capable of neurogenesis.