Schizophrenia

Schizophrenia was a serious mental condition. The condition was often incorrectly generalized as being a "split personality" disorder; although one type of ailment can cause split personalities, there are many different types which cause different ailments, including a prolonged catatonic state.

While examining Doctor Simon Van Gelder aboard the USS Enterprise (NCC-1701) in 2266, Dr. Leonard McCoy performed an electroencephalograph on Van Gelder and managed to rule out schizophrenia as a cause for Van Gelder's madness.