In a letter to the New York Times published on Saturday, Senator Dianne Feinstein (D-Calif.) recommends that the Pentagon review whether the portion of the Army Field Manual that governs the interrogations of “unlawful enemy combatants” should continue to allow the use of “separation” – actually, a form of extreme and potentially abusive isolation – as an interrogation technique.

That’s a great idea, and one that’s long overdue.

As former military interrogator Matthew Alexander explained in an op-ed in the Times on January 21, to which Senator Feinstein was responding, “extended solitary confinement is torture, as confirmed by many scientific studies.” Senator John McCain (R-Ariz.), who wrote about his experience as a prisoner of war in Vietnam, has described the extreme isolation he suffered as “an awful thing” that “crushes your spirit and weakens your resistance more effectively than any other form of mistreatment.” The Nobel prize-winning group Physicians for Human Rights has similarly said that the sort of isolation allowed by the field manual for interrogation purposes may “amount to psychological torture.” It’s called on the Obama administration to revoke Appendix M, which authorizes the technique, and review its contents with human rights organizations.

Human Rights First, in its Blueprint for the Special Task Force on Interrogation and Transfer Policies issued last year, similarly warned that Appendix M of the Army Field Manual risks treatment "known to result in severe psychiatric harm in violation of domestic and international law" and called for a single interrogation standard to apply to all detainees in armed conflict.

We’re not talking here about separating a detainee from other terrorism suspects to prevent collusion or to allow an interrogator to confront one detainee with another’s statements. Those are logical and lawful tactics. But the sort of extreme isolation that Appendix M allows is ultimately designed to “break” detainees mentally. That’s unlawful and inhumane. And it doesn’t produce reliable information.

Although the Army Field Manual limits the first instance of a detainee’s isolation to 30 days, that period can easily be extended simply by the approval of a military general. Based on his military interrogation experience, Alexander predicts that “there will be numerous waivers to even that minuscule requirement.”

Appendix M allows for other forms of abuse as well, such as sleep deprivation, by saying that detainees in isolation must be allowed "four hours of continuous sleep every 24 hours." That still allows for repeated back-to-back 20-hour interrogations.

Although Senator Feinstein isn’t on board with all of Alexander’s criticisms of the field manual, this is the first time that she’s acknowledged that Appendix M allows for the abuse of detainees and should be reconsidered.

She should now use her leadership on the Senate Intelligence Committee to urge the administration to do just that.