That's why I said controlled sensory deprivation. It's a spectrum. Just because it doesn't involve ketamine and float tanks doesn't mean they aren't trying to destroy his brain. First of all there are no indications that he is or has ever been suicidal, so that explanation is laughable. And how exactly is preventing him from doing any exercise supposed to keep him from committing suicide anyway?
What makes you think there's no indication that he's been is or has ever been suicidal? Why would we know about it, if there had been? Is it not plausible that a kid who was pretty screwed up in the first place, who committed treason on a lark, and who is now facing life in prison for betraying his country, might turn suicidal?
The only indication we have one way or the other is that he's on Prevention of Injury watch, which is a pretty good sign that somebody thinks he is.
"When he was first arrested, Manning was put on suicide watch, but his status was quickly changed to "Prevention of Injury" watch (POI), and under this lesser pretense he has been forced into his life of mind-numbing tedium. His treatment is harsh, punitive and taking its toll, says Coombs.
'There is no evidence he's a threat to himself, and shouldn't be held in such severe conditions under the artifice of his own protection.'
"The command is basing this treatment of him solely on the nature of the pending charges, and on an unrelated incident where a service member in the facility took his own life," Coombs said, referencing the February suicide of a marine captain in the Quantico brig. Coombs says he believes Quantico officials are keeping Manning under close watch with strict limitations on his activity out of an overabundance of caution. Both Coombs and Manning's psychologist, Coombs says, are sure Manning is mentally healthy, that there is no evidence he's a threat to himself, and shouldn't be held in such severe conditions under the artifice of his own protection."
C.f. also Glenn Greenwald's column from the other day, where he says:
"From the beginning of his detention, Manning has been held in intensive solitary confinement. For 23 out of 24 hours every day -- for seven straight months and counting -- he sits completely alone in his cell. Even inside his cell, his activities are heavily restricted; he's barred even from exercising and is under constant surveillance to enforce those restrictions. For reasons that appear completely punitive, he's being denied many of the most basic attributes of civilized imprisonment, including even a pillow or sheets for his bed (he is not and never has been on suicide watch). For the one hour per day when he is freed from this isolation, he is barred from accessing any news or current events programs."
So possibly he was on suicide watch for a couple days, but they quickly determined he was not suicidal and have since been taking punitive action against him.
Even relatively mild sensory deprivation can cause fairly severe depression, as I make the case for here: http://news.ycombinator.com/item?id=948637
And what they are doing to him is way more extreme than what most people with depression are accidentally doing to themselves.