I am still very curious about exactly how neurons develop and upon further investigation I found an interesting article that dictates how neuronal development can be considered abnormal. The article titled MR of Neuronal Migration Anomalies can be found here (http://www.ajronline.org/content/150/1/179.full.pdf+html).
In this study 13 patients with abnormal migratory neurons of all severities were observed using Magnetic Resonance (MR) to image the patients due to its high contrast between grey and white matter. Correct neural migration occurs from developing brains to all parts of the body during weeks 8 through 16 of pregnancy. Continual development also occurs until week 25 of pregnancy. However its during weeks 8-16 when the authors concentrate their study. Any injury to the brain during weeks 8-16 alters the migratory pathway of the neuron resulting in abnormalities such as seizures, mental retardation, and developmental delay to identify a few. The researchers also hypothesize that there is a possibility of genetics that plays a key role in the development of neuronal pathways.
The article states that at a specific area in the brain called the cell-sparse layer is most likely where a diversion of normal growth takes place. They believe that necrosis occurs in this area and further hinders the patient because the axons and places of dendritic connection which have already been established are also affected by the necrosis of the cell-sparse layer of the brain. They are able to determine that the axonal and dendritic connections of the white matter have been diminished due to the necrosis in the cell-sparse layer of the brain. This is called "syndromes with lissencephaly" and is still debated between professionals.
There is still much more to this article that explains in greater detail exactly how and why they believe the things mentioned above. I think it is very interesting how they have determined the information and I would really like to learn even more about other anomalies in neuronal migration