Nowadays we know that there are two neurogenic sites in the adult human brain that are able to generate new neurons. These two regions are located A) in the subventricular zone (SVZ), located along the lateral ventricle and B) in the fascia dentata of the hippocampus. Cell organization in the SVZ is well established, there are 3 layers, namely 1) ependymal layer, responsible of cerebrospinal fluid movement, 2) Gap or hypocellular layer, composed of astrocytic and ependymal expansions, but sparse in cell somas and 3) Ribbon layer, where we find astrocytes, identified as the stem cells (type B cells). But migrating cells (type A) moving to the olfactory bulb or transient amplifying cells (type C) present in the rodent have not yet been described in the human brain.

Most of the current data were obtained in rodents, where cell types are well characterized. But we need to know more about the interactions of the neurogenic niche and the factors that regulate it and how these cells could exchange information. In this context, recent studies describe that stem cells contact through a small expansion (a primary cilium) with the cerebrospinal fluid that acts as an antenna. More recently it has been described that stem cells are not randomly distributed in the SVZ, but are organized in the center of "pinwheel" structures composed of ependymal cells.

In conclusion, we still need to know more about the neurogenic niche and its interactions, as well as the molecules involved.