The isolation tank was developed in 1950 by John C. Lilly while doing some studies on brain activity. Dr. Lilly wanted to find out if conscious activity of the brain required outside stimuli. He developed a tank where the subject floated upright with a sensory depriving hood on the head. As up to 85% of all central nervous system activity is caused by light, sound and gravity, Dr Lilly wanted to try eliminating as much of that stimuli as possible. Later, the tank was refined, so the subject could float on ones back, and the hood was not necessary.
John Lilly went on to incorporate LSD and mind altering substances in his experiments with the sensory deprivation tank. As his experiences and theories became more outside mainstream thought, he left the Institute of Mental Health at Bethesda, Maryland and began his work with dolphins and interspecies communication.
Isolation tanks are available to the public now at some health clubs and tanning salons. For a price, one can enter the pod filled with warm mineral water, close the lid, and experience sensory deprivation. I tried one out, and found it amazingly relaxing and stress relieving. I would recommend, however, booking the tank for more than the one hour block. I was not ready to leave after one hour. Acclimating to the tank and becoming comfortable with sensory deprivation takes some time. Whether one is seeking enlightenment or just relaxation, the tank is quite an experience.