For two of his five years in a Vietnamese POW camp, Senator John McCain was locked in a tiny isolation cell, cut off from all human contact. He was beaten regularly and then denied adequate medical treatment for two broken arms, a broken leg, and chronic dysentery. But for McCain something was far worse than physical pain—the pain of isolation. McCain said, "[Isolation] crushes your spirit and weakens your resistance more effectively than any other form of mistreatment."

Medical doctor Atul Gawande points to McCain's experience and then describes a study of nearly 150 U.S. naval aviators who returned from imprisonment in Vietnam: they reported that social isolation was as agonizing as any abuse they had suffered. But what happened to them was physical. EEG studies going back to the 1960s have shown diffuse slowing of brain waves in prisoners after a week or more of solitary confinement

Gawande writes:

Some prisoners whose only social contact was a food tray shoved through a slot became catatonic or developed autistic features. … Still others had panic attacks or became extraordinarily aggressive. These symptoms suggest neurological damage. Neuroimaging studies confirm that isolation creates the same level of activity in the brain as does physical distress; the neural signs of social pain look a lot like the signals created by physical pain. Even months after they were released, MRIs of prisoners of war in the former Yugoslavia showed the gravest neurological damage in those prisoners who had been locked in solitary confinement. Without sustained social interaction, the human brain may become as impaired as one that has incurred a traumatic head injury.