The government has imposed strict laws on how far scientists can use human embryos in research due to the ethical, religious and political connotations that can arise. Animal models however are OK to use nonetheless laws in relation to treatment and care do apply. If these laws are broken you can go to prison! This is why often labs use animals that are not vertebrates such as Drosophila  that are not only cheap to raise and keep but also provide useful models for development as many aspects of their genome is conserved in humans.

The later you look at an embryo, the more processes are set in place and established. A new born baby already has a fully functional wired and working brain. Scientists need to look back as early as possibly in order to establish how the brain forms as it does and why.

In order to understand how the brain works once it is formed, we must understand how it is formed. Many of the developmental processes that take place in early brain development have links to the adult brain and it can highlight the cause of many neural disorders.

Early brain development may seem overly complex, with many signalling cascades and molecules. The embryo has ways to control these factors including signalling scaffolds that hold molecules in one set place; localised membrane signalling via hotspots; inhibitors and activators of many signalling molecules and pathways; negative and positive feedback mechanisms, as well as redundant pathways (back-ups) if it all does go wrong. 

If the redundancy pathways fail, what arises from incorrect brain formation if not fatal, are diseases and disorders seen at birth such a holoprosencephaly and cyclopia; caused by defective Shh signalling and spina bifida: caused by the incomplete closure of the spinal cord.