There are slightly more than 2 million people incarcerated in the United States — that’s nearly equal to the entire population of Houston. Among those prisoners, thousands serve time in solitary confinement, isolated in small often windowless cells for 22 to 24 hours a day. Some remain isolated for weeks, months or even years.

“You’re shut off from the world and you wait,” says Olay Silva, a 41-year-old inmate serving time in Bismarck, N.D.’s maximum-security prison. Silva spent six months in solitary after he was involved in a stabbing. “You just sit there and wait.”

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