Editor's note: Terry A. Kupers is institute professor at The Wright Institute and author of "Prison Madness: The Mental Health Crisis Behind Bars and What We Must Do About It." He testifies as a psychiatric expert in court about prison conditions and the quality of correctional mental health care. He received the exemplary psychiatrist award from the National Alliance on Mental Illness in 2005, and the William Rossiter Award from the Forensic Mental Health Association of California in 2009.

(CNN) -- Army Pfc. Bradley Manning has been imprisoned in the Quantico Marine Corps Brig for nine months, suspected of giving highly classified State Department cables to the website WikiLeaks. He has not been tried, yet is kept in solitary confinement in a windowless room 23 hours a day and forced to sleep naked without pillows or blankets.

Human rights groups have condemned his treatment, and even State Department spokesman P.J. Crowley spoke out against it. Crowley has resigned, allegedly under pressure from the Obama administration. Defense officials say Manning is stripped of his clothes nightly to prevent him from committing suicide, yet his civilian lawyer says his client is at no risk.

The problem with the argument that Manning is being kept in long-term solitary confinement to prevent his suicide is that long-term solitary confinement causes suicide.

One of the most stunning statistics in criminology today is that, on average, 50% of U.S. prisoner suicides happen among the 2% to 8% of prisoners who are in solitary confinement, also known as segregation. When I tour prisons as I prepare for expert testimony in class-action lawsuits, many prisoners living in isolation tell me they despair of ever being released from solitary.

And there is an objective basis to their fear: One of the many psychiatric symptoms known to be bred in solitary is mounting anger, plus the dread that losing control of that anger will lead to more disciplinary infractions and a longer stint in segregation. So the prisoner despairs of ever gaining more freedom, and that despair leads to suicide.

Suicide is merely the tip of the iceberg. Solitary confinement breaks prisoners down and practically guarantees they will never function normally in society again. This explains a troubling rise in the recidivism rate since the advent in the late 1980s of wholesale solitary confinement in "supermaximum"-security prisons.

Long-term solitary confinement causes many psychiatric symptoms, including mental breakdowns. Even the relatively stable prisoner in segregation experiences mounting anxiety, paranoia, an inability to concentrate, somatic symptoms, despair and anger. But the prisoner prone to emotional disorder falls apart.

In a 2009 study by the U.S. Bureau of Justice Statistics, 56% of state prisoners reported symptoms consistent with serious mental illness requiring treatment. And we know from much research in criminology that prisoners with serious mental illness are selectively consigned to solitary confinement -- after all, as a group they are not known for their ability to conform to the rules, and in prison, rules pile upon rules.

The other major stressor leading to suicide or mental breakdown in solitary confinement is the near total lack of contact with loved ones and caring others. Manning's family is in England and cannot visit, and even his visits with his friend, David House, are infrequent or stressful because of the ever-present security precautions that make real connection difficult.

Visits in supermax prisons are typically problematic. The facilities are far from urban centers, the visitor is put through stringent searches, the visitor and prisoner are separated by an indestructible fiberglass window, and the prisoner is kept in chains, even though he is isolated in a separate and secure room. Many prisoners in these circumstances tell me they discourage visits from their family, including their children, because "I don't want them to see me in chains."

What goes on in the isolation prison unit is a secret -- unsurprising if visits are discouraged or difficult, and the media is excluded. The government's secrecy about Manning's condition is consistent with the policy on the part of departments of correction to bar the media from interviewing prisoners and to refuse to release information about the use of stun guns and riot guns in solitary confinement units. This kind of secrecy is a necessary precondition for abuse. Indeed, in my investigations of supermaximum-security units around the country, I find unspeakable abuses, including senseless deprivations of clothing and inappropriate beatings.

Manning is a pretrial detainee. The Constitution requires that innocence be assumed until guilt is proved, and that the defendant in criminal proceedings be provided with the wherewithal to participate in his legal defense.

The Eighth Amendment to the U. S. Constitution bars cruel and unusual punishment, and repeatedly, U.S. courts have found that overly harsh conditions of isolation and the denial of mental health treatment to a needy prisoner are Eighth Amendment violations. In international circles, for example, according to the U.N. Convention Against Torture (the United States is a signatory), the same violations of human rights are termed torture.

Clearly, Manning's treatment violates these constitutional guarantees and international prohibitions against torture. Why? Have we permitted our government, under the cloak of security precautions, to set up a secret gulag where conditions known to cause severe psychiatric damage prevail? As a concerned psychiatrist, I strenuously object to this callousness about conditions of confinement that predictably cause such severe harm.

The opinions in this commentary are solely those of Terry A. Kupers.