Professor Fred Gage explains that neurogenesis only occurs in the hippocampus and the olfactory bulb in humans, and discusses why this might be so.
The hippocampus and the olfactory bulb are areas where neurogenesis occurs in all mammals, so that’s interesting that it persists just in those two areas in all mammals. One of the major questions in the field is, "why would this process of neurogenesis persist only in those two areas?" It’s important to note that cells divide or dividing cells exist in other areas, but they only give rise to functioning neurons in these two areas. So, it is not that there aren’t dividing cells in other places.
The current thinking is the reason why the cells give rise to neurons in just these regions is because the environment that they are in permits this to occur. That is a mechanistic statement. Another sort of question is, not just what are the determining molecular factors that make the cell become a neuron in this area, but why is there neurogenesis, what is the function for neurogenesis in this area? That is an area that is under hot pursuit right now and there is a lot of investigation and it looks like, in the hippocampus at least, neurogenesis is important for, not the acquisition of new memories, but rather the retention or long term retention of memories, because it is occurring in the structure called the hippocampus, which is important for memories.
It also seems to be involved in affective behaviors, in emotional behaviors too. These are the two areas that are important and it seems like neurogenesis is important in the organism’s ability to adapt. So, this adding of new neurons into the brain in this structure is thought of as an adaptive mechanism for adults as well.