An isolation tank (also commonly known as a sensory deprivation tank) is (ideally) a lightless, soundproof tank in which subjects float in salty water (denser than the human body) at skin temperature. It was devised by John C. Lilly in 1954 in order to test the effects of sensory deprivation. Such tanks are now also used for meditation, prayer, relaxation, and in alternative medicine.
The isolation tank is also called float tank, floating tank, floater tank, floatation tank, Samadhi tank, sensory deprivation tank, REST tank (Restricted Environmental Stimuli Therapy), and John Lilly tank.
In the original tanks, people were required to wear complicated head-masks in order to breathe underwater; in newer tanks, Epsom salt (1.30 grams per cubic centimeter) is added so that the subject floats with his or her 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.
A therapeutic session in a flotation tank typically lasts an hour. For the first forty minutes it is reportedly common to experience itching in various parts of the body (a phenomenon also reported to be common during the early stages of meditation). The last 20 minutes often end with a transition from beta or alpha brainwaves to theta, which typically occur briefly before sleep and again at waking. In a float tank the theta state can last for several minutes without the subject losing consciousness. Many use the extended theta state as a tool for enhanced creativity and problem-solving or for superlearning. Spas sometimes provide commercial float tanks for use in relaxation.
Shorter sessions may be relaxing and other benefits are claimed by Lilly but have not been confirmed by other scientists. Common reactions to extended sensory deprivation are hallucinations, out-of-body experiences, anxiety, and depression, and some researchers believe this to be evidence of a deep human need for almost constant input of stimuli (the opposite of Lilly's conclusion).
More extreme uses of the tank involve the subject taking varying doses of hallucinogens, such as LSD, and spending prolonged periods in the tank (up to tens of hours) at a time, an approach pioneered by Lilly himself – though he claims to have tried LSD in the tank only after 1964, when the drug was still legal, a decade after his first experiments with the tank itself.
- Coma Suspension (for a similar experience)