Neurologists know how the brain works in a medical/scientific fashion rather than in a "therapy" fashion. They don't look at psychological dx's like "depression" and then how to cure them, like a psychiatrist might, they look at the whole brain and see what doesn't look "right" and what that might relate to. For example, here's some "pictures" of how your brain might look if you have adhd:

http://newideas.net/adhd/neurology