..well, depression is Chemical, it shows up on a CAT scan, as does Schizophrenia.

Ihave an abnormally high protein level in my spinal fluid that makes me sociopathic and a really fast learner but I'm not going to go into all the boring neurology I've picked up over the years....

I think most emotional and mental ailments are chemical in origin but how the persons brain deals with the particular stimulus dictates their symptoms.
Every brain is different in how it handles stimulus the only thing thay have in common is which part of the brain handles the stimulus.