WASHINGTON » Before he was exonerated of murder and released in 2010, Anthony Graves spent 18 years locked up in a Texas prison, 16 of them all alone in a tiny cell.

Actually, he does not count it that way. He counts his time in solitary confinement as “60 square feet, 24 hours a day, 6,640 days.” The purpose, Graves came to conclude, was simple. “It is designed to break a man’s will to live,” he said in an interview.

An estimated 75,000 state and federal prisoners are held in solitary confinement in the United States, and for the first time in generations U.S. leaders are rethinking the practice. President Barack Obama last week ordered a Justice Department review of solitary confinement while Congress and more than a dozen states consider limits on it. Justice Anthony M. Kennedy, in a Supreme Court ruling last month, all but invited a constitutional challenge.

“Do we really think it makes sense to lock so many people alone in tiny cells for 23 hours a day, sometimes for months or even years at a time?” Obama asked in a speech at a convention of the NAACP in Philadelphia, where he called for an overhaul of the criminal justice system. “That is not going to make us safer. That’s not going to make us stronger. And if those individuals are ultimately released, how are they ever going to adapt? It’s not smart.”

While other changes to the justice system would require Congress to act, this is one area where the president has at least some latitude, although it is uncertain how much. Either way, it could be a test of his drive in his final 18 months in office to remake America’s prisons. In his NAACP speech and during a visit to a federal prison, the first by a sitting president, Obama expressed a concern for the lives of prisoners that few if any of his predecessors have shown.

“No president has ever suggested that there’s anything problematic about solitary confinement, that we should be studying it or that it’s overused,” said Margaret Winter, associate director of the American Civil Liberties Union’s National Prison Project. “I feel like that has got to be some sort of a tipping point.”

The Rev. Ron Stief, executive director of the National Religious Campaign Against Torture, called the moment “a game changer.” He said: “We’ve been saying for decades, ‘It’s time,’ and it really feels now like it is time. The silence has been broken.”

Studies have found that solitary confinement exacerbates mental illness and that even stable people held in isolation report experiencing psychiatric symptoms, including anxiety, depression, anger, self-cutting or other acts of self-harm or compulsive actions like pacing or cleaning a cell over and over.

“When they get out, they are broken,” said Dr. Terry Kupers, a psychiatrist in California who consults on prison conditions and mental health programs. “This is permanent damage.”

Cornell William Brooks, the president of the NAACP, said prolonged solitary confinement amounted to torture.

“Putting someone in solitary confinement does horrible things to a person’s personality, their psyche, their character,” he said. “It might be said that condemning a person to solitary confinement treats a person as an animal. And so that they emerge from such treatment exhibiting animalistic behavior can’t be surprising.”

Many corrections officials, even those who believe that solitary confinement is overused, caution that in some situations, it may be unavoidable.

“If someone has committed a violent assault, whether it be a staff member or another inmate, until you can somehow solve that problem, that person is going to need to be isolated,” said Rick Raemisch, executive director of Colorado’s corrections department. He pointed to an inmate who said he would kill someone if he were allowed out of solitary, a threat mental health professionals considered credible.

Raemisch has worked to substantially reduce the use of solitary confinement in Colorado but said groups that opposed it altogether should help develop other ways to handle inmates who pose a danger of violence.

“There are those that say this is bad,” he said, “but when you look around for an alternative, people have left the room.”

Solitary confinement has been widespread since the 1980s, when many states built super-maximum security prisons. They were intended to hold the most dangerous criminals, but corrections departments, dealing with gang violence and crowding worsened by stiffer sentences, began removing an increasing number of inmates from the general population, including some who did not pose a serious threat.

They sent them to isolation units where prisoners in most cases spent 23 hours or more a day in their cells, often without visiting privileges or access to rehabilitation programs. The solitary confinement unit at Pelican Bay State Prison in California, where some inmates have been kept for more than 20 years, was specially designed to minimize human interaction.

Obama can exert little control over state prison systems, but he hopes that any changes he makes in the federal system will prod states to follow suit.

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