According to wikipedia, it is associated with (doesn't imply causation) physical changes to the brain in 40-50% of cases. I'm not any kind of expert, just reading what I see there, but apart from small decreases in brain volume (not known whether this is preexistent or not), I don't see any mention of the brain "deteriorating". Indeed, it seems that around a quarter of sufferers recover completely, others may have long periods between relapse. It is also possible to suffer schizophrenia with a high intelligence quotient.