The US Federal Bureau of Prisons has agreed to a comprehensive review of the use of solitary confinement in its prisons.
The review will include the fiscal and public safety consequences of the controversial practice.
The National Institute of Corrections plans to retain an independent auditor "in the weeks ahead" to examine the use of solitary confinement, which is also known as restrictive housing.
Prisoners in isolation are often confined to small cells without windows for up to 23 hours a day.
"We are confident that the audit will yield valuable information to improve our operations, and we thank Senator (Dick) Durbin for his continued interest in this very important topic," Federal Bureau of Prisons spokesman Chris Burke said in a statement.
Senator Durbin's office said the practice can have a severe psychological impact on inmates and that more than half of all suicides in prisons occur in solitary confinement.
In his state of Illinois, 56% of inmates have spent some time in segregated housing.
"The United States holds more prisoners in solitary confinement than any other democratic nation in the world, and the dramatic expansion of solitary confinement is a human rights issue we can't ignore," said Mr Durbin, who chaired a Senate hearing on the use of solitary confinement last year.
"We can no longer slam the cell door and turn our backs on the impact our policies have on the mental state of the incarcerated and ultimately on the safety of our nation."
The federal prison system is the largest in the country and includes some 215,000 inmates.
News of the review was welcomed by the American Civil Liberties Union, which is a strong critic of the nation's use of solitary confinement.
"We hope and expect that the review announced today will lead the Bureau to significantly curtail its use of this draconian, inhumane and expensive practice," David Fathi, director of the ACLU's National Prison Project, said in a statement.