I've been reading Alice Flaherty's book The Midnight Disease (now in paperback). It's about mania, depression and the phenomenon of hypergraphia, among other things, and is simply fascinating. Writing about "Literary Creativity and Drive" she says:
"The Greeks, and many since them, emphasized not intelligence, but passion and drive as the fount of creativity. Socrates and others expected poets to receive their ideas in a frenzy, possessed by the Muses. Plato even thought that the sane should not be allowed to write poetry: "He who approaches the temple of the Muses without inspiration, in the belief that craftsmanship alone suffices, will remain a bungler and his presumptuous poetry will be obscured by the songs of the maniacs [italics mine]." " pg 63
In another section she writes about "Primary Process" (the raw, visual, associative, emotion-driven) vs. "Secondary Process" (the abstract, language-based, logical), and how literary creativity needs both: " . . . not only a powerful source for ideas, but a powerful editor to channel them."
And, finally, this quote from sculptor Augustus Saint-Gaudens: "What garlic is to salad, insanity is to art." I, for one, love the garlic.