A man who is isolated and alone can be regarded as a sort of discarded person," Dinizulu, king of the Zulus, wrote in 1910. "There is nothing worse than being isolated." Prisoners who have endured solitary confinement agree. According to Senator John McCain, who was kept alone in a cell as a prisoner of war in Vietnam, "It crushes your spirit."

Others now in this situation have described the experience as a "horrible, caged feeling," or living "in a void of nothingness," as a study by the New York Civil Liberties Union last year found. Yet despite expert consensus that such extreme separation from others can yield effects akin to those of physical torture, it often is employed as a remedy of first, not last, resort. And it has been imposed for weeks, months or years — even decades — with little regulation or due process. Partly to protest the overuse of solitary (also known, among other names, as administrative segregation, "ad-seg" and "special housing"), California inmates mounted a 60-day hunger strike that ended on September 6 without any major concessions on the state's part but with the promise of legislative hearings on the problem.

A few jurisdictions, recognizing the need for change, have lessened their dependence on this counterproductive and expensive practice. (Ad-seg housing costs almost double the price of regular accommodations.) However, with at least 80,000 prisoners nationally still held in virtual seclusion, either within regular facilities or in dedicated "supermax" institutions, real reform will be hard to accomplish.

Solitary confinement typically entails up to 23 hours a day of lockdown in a cell ranging from 36 to 100 square feet. Meals, mail and most mental health and medical care (insofar as they exist) are delivered through a small slot in the door. Very limited exercise periods usually occur in another cage, without company or any form of equipment. Intellectual stimulation is virtually nil, sometimes as little as a pad and a pen; the vast majority of prisoners cannot participate in work or educational programs. Access to sunlight and fresh air may be totally lacking. Excessive sleep frequently amounts to the only escape for the outcast inmate.

Not surprisingly, this ­dehumanization causes many of its victims to suffer from severe symptoms, including chronic depression, panic attacks, paranoia, hallucinations, nightmares and self-mutilation. The effects may be irreversible. The inherent horrors of solitary, moreover, often are compounded by guard brutality, deprivations of food and other necessities, and the gratuitous use of restraints. In the words of an expert in the field, psychology professor Craig Haney, "The best-case scenario is they come out no worse than they went in — and it goes downhill from there."

Indeed, some fail to come out at all. Although isolated inmates constitute less than 10 percent of the prison population (except on death row, where ad-seg is used routinely), they make up about 50 percent of inmate suicides, according to a study released this year by the American Civil Liberties Union. Among those who do exit, a significant number are released directly to the streets. Utterly desocialized, they are most likely to reoffend and endanger the public.

ABANDONED 19TH CENTURY IDEA

Isolation began in about 1820 as a social experiment by the Quakers. Believing that lonely introspection would lead to rehabilitation, they deemed it a more humane alternative to other penalties like capital punishment. Its theoretical basis discredited, the practice was largely abandoned by the end of the 19th century; it re-emerged during the late 20th century in response to deadly prison outbreaks.

Although conceived as a means of housing the worst of the worst, as well as especially vulnerable inmates like homosexuals, security risks and high-profile detainees, it increasingly has been employed against gang members (not just leaders) and convicts viewed as hard to handle for various reasons. In light of the plethora of rules governing every aspect of prison life of which inmates can run afoul, many incur segregation for nonviolent infractions like damaging minor items of property, possessing marijuana, lying or disobeying an order. Even the mentally ill and juveniles have not been exempted. It occurs despite their diminished ability to cope with its rigors and the finding of Juan Mendez, the United Nations special rapporteur on torture, that its imposition on these offenders "always constitutes cruel, inhuman, or degrading treatment."

A number of federal courts have held that isolating prisoners with severe mental illnesses violates the Eighth Amendment. Furthermore, about 1 percent of those being held at the largest immigration detention centers are relegated to isolation, even though they have not been convicted of any crime but are simply awaiting deportation proceedings, according to a March 28 Los Angeles Times editorial.

A few bright signs have surfaced, however. For example, under the leadership of the late director of the Colorado Department of Corrections, Tom Clements, the system there reduced by more than 40 percent its use of administrative segregation. In addition, Clements halved the incidence of direct release without transition. (In an ironic tragedy, he was murdered by a man paroled in this fashion.) Mississippi, Illinois, Maine and Michigan also have substantially cut down on the number of solitary inmates.

Yet much more remains to be done — and punitive sentiments have all too often undercut serious penal reform.

Vivian Berger is Nash Professor of Law Emerita at Columbia Law School.