Zombie Research Society

Zombie Research Society has described the zombie on a scientific way, they also include how their brain works.

The biological reason why zombies are as they are;
The cerebellum is a cauliflower-shaped region of the brain that almost has half the neurons of the entire brain. The cerebellum is responsible for the coordination of movements so you can move smoothly and accurately. With zombies this area is damaged after reanimation resulting jerky movements and balance problems.

Because of the damage to the Inferior frontal gyrus, the zombie himself can not express in speech or writing or understand language (spoken or written). 

If the Wernicke area in the brain (which is responsible for language)has an injury occurs
At a junction of the two brain lobes, temporal and pariëtiale. We have not the ability to understand spoken or written text. Zombie also sufferd this damage during reanimation.

http://zombieresearchsociety.com/archives/9340