This dissertation is a history of scientific experiments in isolation, conducted by psychologists, psychiatrists, and neurophysiologists in laboratories across North America between 1951 and 1969. Begun at McGill University by psychologist Donald Hebb and rooted in an early Cold War imaginary of sophisticated Soviet methods of interrogation and indoctrination, these experiments made solitary confinement into an experimental technique. Interpreted and replicated by Air Force scientists working within the nascent discipline of space medicine, experimental isolation was further key to the formation of the remote and hostile environments on which the Cold War might be fought, suggestive of new psychological hazards posed by the monotony of warfare conducted in the nominal loneliness of outer space. However, what emerged from this project was far larger than these points of origin: a new conception of the subject as always already entangled with their immediate environment at the level of both brain and ego, obtained via the rough severing of an organism from its milieu.