The Netflix hit “Stranger Things” returned for a fourth season this month. As always, it is jam-packed with tropes and cliches drawn from ’80s movies. One recurring reference this season is the use of mental hospitals and asylums.

This fascinates Troy Rondinone, a professor of history at Southern Connecticut State University who wrote a book on this phenomenon: “Nightmare Factories: The Asylum in the American Imagination” (Johns Hopkins University Press, 2019).

Rondinone calls himself “a historian of culture” who has watched “literally hundreds of movies with asylums in them.” “Nightmare Factories” was his third book; his others are about popular culture visions of labor issues and boxing. He writes a blog, “The Asylum,” for Psychology Today magazine’s website, which has recently covered representations of mental health in “Frankenstein” and the recent movie “The Batman.”

“Asylum used to be a good word. It meant a safe haven,” Rondinone explains. “But it gained negative connotations, so by the 1800s, they started calling them hospitals.

“In the 1930s and ’40s there was a reform movement, and that was generally a good thing. New hospitals would be opened, with better ventilation, more restful environments. What they didn’t talk about was recidivism. By the late 1800s, the system wasn’t working. Hospitals were filling up and people were staying longer. This is when ‘the living dead’ become a metaphor for the patients and ‘heroic therapies’ like injecting serum or lobotomies were happening. They put people into a stupor but figured a stupor was good enough.”

Rondinone’s interest in cinematic presentations of asylums is American-centric, distinct from the many British, European and other perspectives. “Stranger Things” didn’t make it into his “Nightmare Factories” book (which concentrates on film, not TV), but Rondinone has followed the show faithfully and notes that it pays homage to iconic asylum scenes that he does discuss in the book.