Oliver Sacks Discusses "The Man Who Mistook his Wife for a Hat."

Oliver Sacks suffered a severe injury while hiking which eventually led to the loss of feeling in his leg. His recovery and gave him insights into the treatment of his own patients who suffer from memory problems and encephalitis lethargica.

The famed neurologist talks to Fresh Air about how grief, trauma, brain injury, medications and neurological disorders can trigger hallucinations — and about his personal experimentation with hallucinogenic drugs in the 1960s.

Neurologist Oliver Sacks is famous for his case studies of people with neurological disorders that cause unusual problems with perception. In The Mind's Eye, Sacks turns to himself, explaining how an eye tumor affected his vision and perception of the world.