Solitary confinement is pretty much the one and only placement that prisons use as punitive measures for rule infractions. Their idea for a behavior modification is placing you in a concrete box with your toilet next to your concrete bed, a very small slit for  window to look out of at another concrete wall.  All your tools to stimulate your mind are stripped from you and  limiting our ability for communication and contact with others and our loved ones.
In Washington's State IMU, it is a rule violation to talk to another through your cell's air vent or while you are out for your rec period for an hour.  If you do , your rec is terminated and you will be written up , extending your time in solitary confinement.  How these highly educated prison administrators concoct these ideas is beyond my grasp of reasoning, and to continue to isolate prisoners for months, years , decades !! Last time I spent nearly 10 years in IMU, 90 % of my incarceration has been in solitary confinement. In the BOP, sometimes, it was based on someone's word, usually a rat's, and even without a write up, BAM!! carted off to the hole awaiting a transfer to another facility in another state. I cannot even begin to describe the emotional and mental torture is beholds the prisoner and their loved ones.
The reality is the higher the security of the prison, the more funding and money they receive. The idea of a person locked in a cell with minimal contact with humans, and when it does happen you are cuffed up, is somehow more dangerous than an angry inmate in general population is mind boggling. Most of the prisoners in solitary are not there for violent causes, most are there for dirty urines or bizarre behaviors. So, they tend to treat drug addicts and mental illness in solitary confinement.
For many the mental strain is unbearable. For hours on end they will scream, kick doors and walls. I have seen many men literally lose their minds in here.
Prison is not about rehabilitation. Rehabilitation falls solely on the individual. Most who come to prison , the placement turns them into a hostile, broken man , more so than they were prior to coming. Especially the young.  I have heard many talks over they years, but at ground zero , in the facilities I have been housed in , I have not seen it. At times, they will place a price on your rehabilitation. I can not tell you how many times I have heard,  "Jarnagin, we will let to do ....but only if you ....." which usually meant, compromising my values and morals.  You talk with us about this or that and we will let you do this or that....no thanks, I am good.