Serious brain research lags far behind research of other illnesses, but we know enough now to know that many mental illnesses are real, biological illnesses. I have two sons. One is an AF pilot. The other has Schizophrenia. It is a real biological illness, as are many other "mental" illnesses like biPolar, Depression, etc. His illness just happens to affect the brain, which in turn affects complex behaviors. It's why I have been teaching this for over 12 years:
Family to family