This is a picture of an embryonic mouse brain, in a region called the cortex.  Nuclei of the neural progenitor cells are stained reddish pink. These cells are proliferating to give rise to many other cells (with blue stained nuclei).  The green stain marks the intercellular junctions between cells. Proper cell division in this tissue is critical for correct brain development. The human cortex at this stage has a similar structure and function; thus mouse models can be effectively used to study human brain development.