Oliver Sacks explains the difference between natural and induced hallucinations.

Question: How do you distinguish natural hallucinations from drug-induced hallucinations?Oliver Sacks:  The hallucinogenic drugs always produced visual hallucinations. I think auditory and musical hallucinations are pretty rare. And the visual hallucinations will sometimes start off as geometric patterns and colors, and then one would see landscapes and sometimes enormous crystals or fields of flowers. And I think they were a little bit like opium dreams. Although, in other ways, these drug hallucinations are not like dreams. You’re not asleep; they’re next to consciousness.

A lot of my awakenings patients, when they took L-dopa for their Parkinson’s, would have hallucinations.

Recorded on: Sep 4, 2008