Is solitary confinement torture?

Whilst on the subject of compassion, I came across a fascinating article in the New Yorker suggesting that solitary confinement is a form of torture. Some refer to it as a "living death". It would appear that being locked up all day in a tiny space for years on end eventually turns you into a vegetable.

I'm no liberal, but I'm not sure about the merits of locking up Zacarias Mousssaoui, Richard Reid and others for 22 hours a day. These guys should be reminded every day for the rest of their lives about what they did, but after several years in solitary, I'm not sure that Mousssaoui will be be in a mental state to be aware of anything.