Solitary gets a second look.

• Position: TRENDS & TRANSITIONS

As many as 82,000 inmates are in solitary confinement in state and federal prisons today, but the practice has come under increasing scrutiny. Some lawmakers, psychologists and even prison officials argue long-term isolation is overused, inhumane and expensive.

Solitary confinement, also called administrative segregation, varies from state to state, but the central concept is the same: Inmates are confined to a cell for all but one or two hours a day for a shower and exercise. Contact with others is limited, and meals are provided through the cell door. It can last from a few days to several years, and is used generally for three reasons: to punish a prisoner for violating rules, to segregate a prisoner who might harm others, or to protect a prisoner from being harmed by others. Also, it may be the only housing option in some states and the federal system that bar juveniles from having any contact with adult inmates.

Solitary confinement was used as a short-term punishment for much of the 20th century. That changed in the 1980s, when the U.S. prison population exploded and officials used extended stays in solitary to help manage the growth. Those who support the practice argue it is needed to provide discipline, control behavior, prevent violence and protect inmates.

Concern centers on the harm it might cause prisoners, as several studies indicate inmates who have been isolated for long periods often report paranoia, aggressive fantasies, chronic depression, hallucinations and suicidal thoughts.

Critics also point out it is expensive because it requires more single cells and staff. Colorado has estimated it will save nearly $8 million over two years by closing a prison in 2012 that housed only...