Three years after U.S. Army Private First Class Bradley Manning was arrested in Iraq and accused of providing WikiLeaks with 700,000 intelligence documents and videos, many of them classified, his court-martial has begun. Manning, 25, faces life in prison if he is convicted of aiding the enemy, along with 21 other charges related to what has been deemed the largest leak of classified information in American history. Looming over the testimonies and accusations that are sure to fly between prosecution and defense during Manning’s trial is the knowledge that whatever sentence he receives will be cut down by 112 days—not much against the potential time he faces—because back in January a military judge deemed Manning’s pretrial detention treatment “excessive.”

So what, exactly, is excessive or extreme solitary confinement, and what does one do to deserve it? Experts say that while the technically undefined “extreme” versions of solitary confinement are rarely applied, prisoners across the country are often subjected to exaggerated isolation conditions. These are so severely harmful to their mental health, the experts say, that they may spark the violence they were created to prevent while also violating a prisoner’s Eighth Amendment right to be spared cruel and unusual punishment.

After Manning’s arrest on May 29, 2010, he was transferred to a Marine brig in Quantico, Virginia, where, during his nine-month stay, he was reportedly held in solitary confinement for 23 hours a day, forced to sleep naked without pillows and sheets on his bed, and restricted from physical recreation or access to television or newspapers even during his one daily hour of freedom from his cell, all under the pretense that the private was a suicide risk. Manning’s treatment while in prison sparked as intense a public outcry as his arrest itself—drawing comparisons to the conditions of suspected terrorists at Guantánamo Bay.

Craig Haney, a psychology professor at the University of California, Santa Cruz, who specializes in the psychological effects of imprisonment, said he could think of no other word to describe Manning’s treatment in detention than “inhumane.”

“The practice of leaving someone naked in a cell is not a justifiable correctional practice—and certainly not for more than a very limited period of time,” Haney told The Daily Beast, adding that depriving a prisoner of a pillow or blanket is “beyond the pale.” Prisoners placed on suicide watch typically are stripped of their clothes only temporarily, until they can be provided with a suicide smock that prevents them from harming themselves while still giving them some sort of privacy. And even then, suicide watch usually lasts for just a few days before the prisoner is sent back to his or her regular cell or some sort of rehabilitation facility. “It is unheard of for someone to be on suicide watch for nine months,” Haney said. Solitary confinement, on the other hand, could go on for that long.

Most solitary-confinement cells are nearly indistinguishable in size from a regular prison cell—about 80 square feet, Haney explained. But while regular prisoners spend most of the day in classrooms, work programs, the library, or out in the yard exercising—all the while interacting with one another—they are really only in their cells at night to sleep. A prisoner in isolation usually spends 22 to 23 hours a day in a cell. Isolation cells are equipped with sinks, toilets, and in some cases even showers so that the prisoner hardly ever has to leave. While the rest of the prisoners eat together in a cafeteria or mess hall, a correctional officer slides a tray through a slot in the door of the solitary cell two or three times a day so that the isolated prisoner can eat, alone. The one or two hours a day an isolated prisoner is allowed out of the cell is usually used for recreation, but even then prisoners are often confined to individualized outdoor spaces, referred to as cages or dog runs, that are enclosed so that they can be used by only one prisoner at a time. Whenever a prisoner is taken out of an isolated cell, he must first put his hands through the same slot through which his food is served, to be restrained by a guard.

“It’s a stark and psychologically painful existence,” said Haney. “Your contact with the outside world is typically limited to noncontact visiting. You can’t hug anybody or shake hands. The only time you have physical interaction with a human is when you are put in or out of restraints.”

Except for rare, extreme cases, solitary confinement is not something a judge would mandate as part of a prison sentence. It is determined by the correctional facility, usually as a result of a serious infraction of prison rules or a buildup of several smaller infractions. Solitary confinement may be assigned originally for a few months, but as many prisoners react negatively to the conditions, they may continue to rack up infractions that could keep them isolated for years.

About 2.3 million people are incarcerated in the United States, and an estimated 80,000 of them are in solitary confinement, with their conditions varying widely from state to state and prison to prison. That number does not include the number of prisoners held in the more extreme type of solitary confinement, relegated to separate housing units reserved for those for whom simply the ability to communicate with others presents a severe threat to the safety of the facility. Haney said rarely is a prisoner considered such a threat and that probably only a handful of prisoners in the country exhibit behavior that justifies this kind of confinement. But what about those whose conditions aren’t justified?

Terry Kupers, a psychiatrist who has studied the mental effects of solitary confinement on prisoners, explains that the so-called Supermax facility, or cellblock dedicated to isolation, was created in the 1980s as a way to deal with the uncontrollable violence in prisons caused by overcrowding. Though the Supermax prisons were set up initially to separate the worst from the rest—the rare few Haney described—they were expanded. Pelican Bay State Prison in California, ranked one of the worst in the country, has 1,500 prisoners in its isolated Security Housing Unit.

Jules Lobel, president of the Center for Constitutional Rights and professor at the University of Pittsburgh Law School, is representing about 500 prisoners in a class-action lawsuit against Pelican Bay. By being held for more than a decade in solitary confinement, he said, the prisoners have been subjected to torture and the violation of their Eighth Amendment rights. While Lobel explained that there is no explicit definition of “extreme solitary confinement,” he considers three factors to determine whether a prisoner’s isolation is extreme.

The first is the length of time they’re forced to spend in isolation—a period of several years versus a few weeks or months. The second is the level of isolation, whether a prisoner is allowed to participate in programs with other people or what kind of contact he has with the outside world. “At Pelican Bay, they get no phone calls. That’s extreme,” said Lobel. “In Bradley Manning’s case, I believe, he was shut up very severely from the outside world and other prisoners.”

Then there is what Lobel calls “the draconian nature of the conditions.” By that he means solitary confinement is intended to be preventive, not punitive. “But throughout the United States and at Guantánamo, and in the case of Bradley Manning, who has not been convicted of anything, extreme solitary confinement is used as a punishment. At Pelican Bay, there are no windows, and there is no reason not to have windows. So conditions are way harsher than what’s necessary.”

Lobel emphasizes the importance of understanding that a person who is not beaten or deprived of food can still be subject to mental torture. And that’s exactly what Kupers says he believes is wrong with the solitary-confinement program in general. Kupers, who specializes in forensics and social-community psychiatry and who has studied the mental effects of solitary confinement on prisoners, says the more isolated a prisoner is from the outside world, the greater toll it takes on his mental health. “Isolation itself is very damaging, and there is no way to ameliorate it,” Kupers told The Daily Beast. “People need to be taken out of isolation and put into rehabilitation programs. If you remove the solid steel doors and give them bars, that’s slightly better, but it doesn’t ameliorate the conditions.”

Approximately 50 percent of all suicides at state and federal prisons across the country are carried out by the 2 to 8 percent of prisoners who are isolated. That’s because, as Kupers explained, the mental effects of suicide can range from paranoia and claustrophobia to full-blown mental illness and deterioration. Kupers pointed to the killing of Colorado prison chief Tom Clements by a former inmate who’d just been released from seven years in prison—five of which he spent in solitary confinement—as a perfect example of how isolating prisoners makes them more dangerous, not less. “You put someone in solitary for life and they will deteriorate and no one will notice,” Kupers said. “But if they are going to be released, they are now a disturbed and potentially dangerous person.”