John C. Lilly, a medical practitioner and neuro-psychiatrist, developed the flotation tank in 1954. During his training in psychoanalysis at the US National Institute of Mental Health (NIMH), Lilly commenced experiments with sensory deprivation. In neurophysiology, there had been an open question as to what keeps the brain going and the origin of its energy sources. One hypothesis was that the energy sources are biological and internal and do not depend upon the outside environment. It was argued that if all stimuli are cut off to the brain then the brain would go to sleep. Lilly decided to test this hypothesis and, with this in mind, created an environment which totally isolated an individual from external stimulation. From here, he studied the origin of consciousness and its relation to the brain.
Tank Design & Usage
In the original tanks, people were required to wear complicated head-masks to breathe underwater and uncomfortable tight clothing that constricted the blood flow in certain areas, but the mask and clothing detracted from the isolation experience. The tight fit of the mask seal around the face and the retention strips wrapping around the back of the head were uncomfortable in long sessions. The constant hissing of the air valves and bubbling of exhaust air out of the mask prevented the possibility of silence. The faceplate of the mask was typically solid black for visual isolation, but then the tank user needed help entering and leaving the isolation tank since the mask blinded them. The tight neoprene clothing was extremely uncomfortable in sensitive areas such as the genitalia, and constricted blood flow and mobility in other areas.
In newer tanks, epsom salt is added to the water in the tank to increase the density of the water so that the subject floats with the face above the water. However, since the ears are submerged when the subject is in a relaxed position, hearing is greatly reduced, particularly when ear-plugs are also used. When the arms float to the side, skin sensation is greatly reduced because the air and water are the same temperature as the skin, and the feeling of a body boundary fades. The sense of smell is also greatly reduced, especially if the water has not been treated with chlorine.