Tim Verstynen & Brad Voytek put together a scenario for TED-Ed, trying to diagnose a zombie using medical logic.  The only logic I know is that zombies want to eat my brain, and that's bad for me.

Their premise is simple:

Zombies eat brains. They are also, like all of us, driven by brain functions. What is happening in their brains to make them act as they do? Let's apply the various human medical possibilities that make zombies...zombies.