Michael Rossato-Bennett initially thought it was the worst job he had ever taken.
The filmmaker was flabbergasted when he entered a nursing home on a commission to film a few clips for a website.
"I walked into these hallways with hundreds of residents in wheelchairs just sitting on the side of the hallway, and I had felt like I'd entered into Dante's 'Inferno,'" he said.
That visit, though, eventually sparked "Alive Inside," an award-winning independent documentary on musical therapy for those suffering from Alzheimer's disease and other neurological ailments.
When Rossato-Bennett started filming three years ago he met Henry. The 94-year-old man was crumpled in his wheelchair with his head down, eyes closed and hands clasped. He had been in a nursing home for a decade and couldn't recognise his daughter.
But when a nurse put headphones over Henry's ears and played his favourite music, he began to shuffle his feet, move his arms and sing.
"It was like a resurrection of life in a person," Rossato-Bennett, 53, said. "Then when we took the headphones off the guy, and we started talking to him, the being revealed itself. He had this incredible voice and he spoke poetry, like greater poetry than I'm capable of."
Henry's story, which went viral a few years ago when the video clip was released online, is a common occurrence in the film that has begun its rollout into US theatres this month after winning the audience award for top US documentary at the Sundance Film Festival in January.
The documentary chronicles New York social worker Dan Cohen's effort to bring such therapy to dementia patients as a way to lessen the use of medication and combat its cost on a strained healthcare system about to absorb aging Baby Boomers.
Cohen, the 62-year-old founder of Music & Memory, a programme that seeks to make musical therapy a standard part of nursing home care, began using the treatment in 2006.
"It was just an instant hit," Cohen said with a snap of his fingers. His programme is now in more than 600 facilities worldwide.
Music, which targets areas of the brain not affected by dementia, brings back a sense of identity to dementia patients neurologist and author Oliver Sacks says in the film.
"If you give somebody music for an hour, they're going to be in a better mood for the day, which is really no different if a relative visits," Cohen added.
The film shows patients singing and dancing, seemingly re-animated while listening to music. At one point, Henry sings in the scat style of jazzman Cab Calloway, his favourite singer.
"When people see this they get it," Cohen said.
Many of the subjects, which also includes a woman with schizophrenia and bi-polar disorder, show deep emotional resonance to the music.
"Music is a companion to our becoming," Rossato-Bennett said. "So to enter the desert of soul and bring back something that precious is a great gift."