Solitary confinement is torture. Watch these inmates describe what it’s like.

A United Nations report called it torture. Some victims have claimed it’s hell. Yet prisons keep using solitary confinement as a way to punish inmates.

In a new video from the New York Times’s Colin Archdeacon and the Center for Constitutional Rights, inmates from the Pelican Bay State Prison in California discussed the heartbreaking reality of being alone in a small cell for decades. The inmates, some of whom spent 20 years or more in solitary confinement, described a common theme: They felt they had been caged like animals, not human beings.

“Everything around you becomes numb sometimes,” Paul Redd, who spent more than 11 years in solitary confinement, said. “It’s not to the point where you want to commit suicide. But sometimes I get to the point where I want to go right to the jury and say, ‘Give me the death penalty. Give me the death penalty.’”

Solitary confinement involves putting someone in a cell for days, weeks, months, or even years with little to no contact with others. It is often used to discipline wrongdoers in prisons, but it’s also deployed to protect inmates from others and segregate groups of people who are causing trouble. Around the country, it’s used even to contain juvenile inmates in both youth detention centers and adult prisons.

A large body of research shows that solitary confinement can worsen mental illness and cause it in some circumstances, particularly among younger people whose brains are still developing. Symptoms include hypersensitivity to stimuli, perceptual distortions and hallucinations, anxiety, revenge fantasies, rage, appetite and weight loss, heart palpitations, headaches, problems sleeping, self-mutilation, suicidal thoughts, and, in rare situations, lower levels of brain activity.

Some of the research goes back to the 19th century. The early research about the health effects was so convincing that the US Supreme Court confidently stated in 1890 that solitary confinement is not “a mere unimportant regulation as to the safe-keeping of the prisoner.” The court concluded that solitary confinement caused prisoners to go “into a semi-fatuous condition, from which it was next to impossible to arouse them, and others became violently insane; others still, committed suicide; while those who stood the ordeal better were not generally reformed, and in most cases did not recover sufficient mental activity to be of any subsequent service to the community.”

These detrimental effects extend to people who are in solitary confinement at no fault of their own. In adult prisons, juvenile and transgender inmates are often put in isolation for their own protection against older or bigoted prisoners. Sometimes, certain tattoos can get a person thrown in solitary confinement, because the body art is often associated with gang affiliation.

The American Civil Liberties Union and other reform advocates say it’s time to acknowledge this research and stop the widespread use of solitary confinement. “We have to use data and science in our criminal justice system,” Amy Fettig, senior staff counsel for the ACLU’s National Prison Project, said in February, “in the same way that we do in many other aspects of public policy.”