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Is insanity the secret companion to ­genius? Though we can't very well perform psychological examinations on those who are long dead, that hasn't stopped historians from speculating about the mental conditions of deceased geniuses by interpreting their personal letters, their works and others' accounts. It turns out some of the world's greatest geniuses were quite mad. In fact, some scientists claim that a far greater percentage of creative types (poets, painters, musicians and the like) have been afflicted with bipolar disorder than the general ­population. Some of the world's most renowned creative minds, including writers Mary Shelley, Virginia Woolf, and Ernest Hemingway; composers Irving Berlin and Sergey Rachmaninoff; and painters Paul Gauguin and Jackson Pollock are all believed to have suffered from the illness [source: Patient Health International].

Let's take a look at these mad geniuses -- the famous thinkers and artists who may have experienced mental illness.