@256bmay33: There are different types of mental and neurological disorders which affect the brain. These conditions require a medical diagnosis. Some disorders are inherited, while some are acquired, some have begin in childhood, while others later in life. Management/treatment options such as drugs, psycho-therapy etc are available depending on the type and severity of the disorder. However, some disorders have no cure.
Hmm..first, the brain is a very complex organ. Also, there are lots of different mental/neurological diseases. So: it is hard to know specifically what has happened as it is all on a case by case basis. Whether or not it is cured is dependent on what the illness is, and how well it is being managed (ie: via therapy, medication, etc etc.)