A float tank, also called a sensory deprivation tank or isolation tank, is a lightproof, soundproof box holding a shallow pool of body-temperature saltwater loaded with Epsom salt (magnesium sulfate) at a concentration that lets your body float without any effort. A typical modern float pod holds about 10 inches of water with 1,000 pounds of dissolved Epsom salt, making the water so dense that you cannot help but float. The temperature is kept at about 93.5 degrees Fahrenheit, the point where your skin stops reliably telling where your body ends and the water begins. In the tank, touch is gone, temperature is gone, gravity is gone, light is gone, sound is gone. Your nervous system, which normally spends a huge share of its capacity tracking the outside world, suddenly has almost nothing to track. What rises into that absence is the mind itself, unfiltered, undistracted, with the usual reference points of body and environment removed.
The float tank was invented in 1954 by John C. Lilly, a physician and neuroscientist at the National Institute of Mental Health who wanted to know what the brain does with no outside stimulation. Neuroscience at the time assumed the brain was basically a reactive machine that needed outside input to stay conscious. Lilly's float experiments disproved that: his subjects did not black out. They became more aware, of their own mental activity, of subtle sensations that outside noise normally drowns out, and eventually of states that Lilly, who also researched psychedelics heavily, described as contact with other dimensions of intelligence. He wrote up his experiences in 'The Center of the Cyclone' (1972) and 'The Deep Self' (1977). His later career grew increasingly eccentric, but his core insight, that the float tank is a way to explore the mind's own activity, has held up across decades of later research.
Today's research on floatation REST (Restricted Environmental Stimulation Therapy) is centered at the Laureate Institute for Brain Research in Tulsa, Oklahoma, led by Justin Feinstein. His lab has run the most careful brain-imaging studies of floating to date, using functional MRI scans of people before and after float sessions. A 2018 study in PLOS ONE found that a single 90-minute float session significantly reduced anxiety and significantly raised feelings of serenity, happiness, and contentment across a broad group of people, with especially strong effects in those who had clinical anxiety disorders and PTSD. The imaging showed that floating reduced activity in the amygdala and increased the connection between the prefrontal cortex and the limbic system in ways that fit with lower anxiety. A 2021 study by the same group found that floating significantly increased default mode network activity during the float, but not the usual worry-and-rumination kind. It was a different quality tied to insight, imagination, and spontaneous self-awareness, which the researchers called 'the floatation mind-wandering state.'
Experienced float users, many with hundreds or thousands of hours in the tank, describe a consistent arc. Early sessions bring restlessness, boredom, anxiety about floating, and the surfacing of old mental and emotional material. The mind, cut off from its usual distractions, turns inward, and what it finds there can be uncomfortable. Many first-time floaters run into anxiety, boredom, or old memories they had been unconsciously avoiding. This is not failure. It is exactly what should happen. With regular practice, most serious floaters go weekly or every other week, the early restlessness gives way to deeper and deeper stillness. Long-term floaters report experiences that overlap a lot with the advanced meditation states described in traditional texts: absorption, unity, deep clarity, and occasionally, with no drug involved, experiences that can only be called mystical.