Dr. Carl Bennett is a Canadian surgeon who invites Sacks to observe and document his surgical practice while living with Tourette syndrome. His story is told in the essay “The Surgeon.” While in a “flow state,” Bennett can suppress his tics, especially during surgical procedures and other activities that require intense concentration. He defies Sacks’s expectations of what a person with Tourette syndrome can achieve while also serving as an example of the way neurological conditions can “double” or split an individual’s identity.

Chris Marris is the special education teacher and mentor to Stephen Wiltshire in “Prodigies.” Marris takes a keen interest in Stephen, encouraging him to continue drawing and sharing his work while also incorporating lessons in language into his artwork in the hopes he will eventually become more verbal. Sacks eventually comes to believe that Marris’s diminished presence in Stephen’s life after taking another job causes Stephen pain; he thus indirectly serves as a window into the emotional life of someone with classical autism.

Magnani is an Italian artist and immigrant living in San Francisco, as detailed in “The Landscape of His Dreams.” Magnani is obsessed with painting and talking about his home village of Pontito in Italy, creating artwork out of his near-photographic recollection of the town before World War II.