Is there a meaningful difference between you and your brain?

My brain is much smarter than me.

This is a tough question. Especially, when you consider diseases like FTD which can change your actual personality.

But this is essentially the classic mind-body problem. I would surf around amazon for some related books about mind/body and consciousness. But for the record, I believe in the Gestalt, that the mind is more that the sum of the parts of the body in which in exists.

As a psychiatric social worker who does a lot of medication management for the severely mentally ill, I think that it's not the medication that changes you--it's the disease. The medication allows you to be closer to who you would be without the disease.

There was a recent profile in The New Yorker called "Two Heads" about a philosopher couple whose work is dedicated to exploring this very issue.

Ultimately, behavior (and your personality) is just the complex interaction between the various regions of your brain. We think of the personality as separate from the brain only because the connections are too complicated for us to understand all at once. However, there have been many fascinating cases in neurology where certain regions of the brain are inactivated (usually due to pathological events like strokes, aneurysms, or traumatic brain injury) that have profound effects of personality and cognition. The "seat of the personality" is thought to be localized to the frontal lobe and lesions there cause drastic changes in personality and temperment (read up on Phineas Gage, the classic case).

The biological explanation for the mental illness is a very rare and drastic case but consider that the current legal process has different rules for the "insane" than it does for the non insane. I would think that the tumor argument is fairly analogous to that.

As for the medication for mental illness, one of the ways that certain drugs work are by modifying the synaptic connections in the brain. It takes theraputic levels for long periods of time (usually about a month to build up) before these connections can be made more permanent. Alcohol is no different. People who take alcohol regularly and for long enough change both their brain and their personality. Their brain becomes wired to require alcohol for it to function properly (alcohol is one of the few drugs where complete withdrawal -- ie cold turkey quitting -- for an addicted person can actually kill you) and they exhibit behaviors of addiction. If you take away the alcohol the addicted behavior is still present.

Two very interesting books to read are Oliver Sacks "The Man Who Mistook his Wife for a Hat" and VS Ramachandran "Phantoms in the Brain"

There is none whatsoever. Save for we can perceive our brain’s function.