Sensory deprivation

Sensory deprivation using floatation tank
Sensory deprivation using floatation tank

Sensory deprivation, or Restricted Environmental Stimulation Therapy (REST), is a technique by which sensory input (sound, light, smell, etc.) is minimized.

This practice encourages an extremely deep level of relaxation. REST is typically conducted in a float tank, in which the person is suspended in a solution of warm water and Epsom salt without sound or light. This relaxation technique produces significant physical and mental benefits.


In the 1950s, sensory deprivation experiments were conducted to determine the effects of restricted environmental stimulation on mental and physical functions.

For 24 hours a day, students were confined to a bed in cramped cubicles with their vision and hearing blocked by various means, such as opaque goggles and U-shaped pillows around their heads. The students’ physical and psychological functions quickly deteriorated under these harsh conditions.

In 1954, Dr. John Lilly, a neurophysiologist at the National Institute of Mental Health in Bethesda, Maryland, developed the Floatation Restricted Environmental Stimulation Technique. By suspending a person in water, external stimuli (such as light and sound) were reduced almost completely, but without the harsh conditions of similar experiments.

Dr. Lilly refined his technique between 1960 and 1970, allowing subjects to float freely in an Epsom salt and water solution contained within a dark soundproof chamber. The solution was warmed to skin temperature so that the person would not react to cold or heat.

From his experiments, Lilly determined that such external stimuli as gravity, light, sound, and touch accounted for 90% of the central nervous system’s workload.

Although extended sensory deprivation could be harmful, extended sensory overload could also have detrimental effects on a person’s mental and physical well-being. By reducing excess stimuli appropriately, he could actually lower stress levels.

Drs. Peter Suedfeld and Roderick Borrie of the University of British Columbia began experimenting on the therapeutic benefits of this technique in the late 1970s. However, they renamed the technique Restricted Environmental Stimulation Therapy (REST) or, more appropriately, Floatation REST.

Since that time, several studies have been conducted on the benefits of Floatation REST, as well as other forms of REST. The consistently positive findings of these studies have led to the incorporation of Floatation REST into physical and mental health care programs, as well as fitness training and professional sports medicine.

Currently, floatation centers can be found in major cities in Asia, Australia, Europe, and North America. Individuals can also purchase float tanks for their homes.


Floatation tank
Floatation tank

Floatation REST has many physical and mental benefits because it provides an unparalleled level of relaxation. With the elimination of external stimuli, the central nervous system’s workload is reduced by as much as 90%.

This reduction draws a person’s energy inward and promotes relaxation (the parasympathetic response). The parasympathetic response is the mechanism by which the body naturally regenerates itself and maintains chemical and metabolic balance. Old wounds and injuries are allowed to heal faster.

Increased T-cell production strengthens the immune system. This deep level of relaxation also benefits the cardiovascular system. Known as the vasodilatory effect, the body’s circulation is increased while the blood pressure and heart rate are reduced.

Furthermore, the elimination of gravity on the body allows muscles and joints to release tension and heal more rapidly. For this reason, people suffering from musculoskeletal and rheumatic conditions greatly benefit from Floatation REST, as can women throughout the length of their pregnancy.

As the brain relaxes into a theta state, endorphins are released into the bloodstream, reducing pain and fatigue.

The increased endorphin levels also promote a general sense of well-being and happiness and therefore increase vitality and further reduce levels of stress and tension. The blood levels of stress hormones such as adrenaline and cortisol are reduced by various body messages, receptor site activity, and organ processes.

Combined, these positive effects help reduce the risks of high blood pressure and cardiovascular disease. Stress-related health problems as migraine headache, hypertension, and insomnia are similarly reduced.

The brain, freed of external stimuli, begins working more efficiently. This change provides the floater with an accelerated ability to learn, process information, and use his or her creative mind.

This increased level of mental performance and concentration can be carried over into daily life. Equally important, Floatation REST can help with eliminating compulsive behaviors such as alcoholism and smoking. People with psychological and emotional problems as anxiety and depression can also benefit from this therapy.

An added benefit to Floatation REST stems from the Epsom salts used to provide buoyancy. According to the Archangel Vitamin, Health, and Nutrition Center’s Health Newsletter, Epsom salt “draws toxins from the body, sedates the nervous system, reduces swelling, relaxes muscles, and is a natural emollient (and exfoliative).” Also, because the solution does not leach salt from the skin, the floater’s skin will not wrinkle during the treatment.


Modern float tanks are large enough in size and shape to allow a full-sized adult to easily enter, exit, and lie comfortably. The bottom of the light-proof and sound-insulated chamber is filled with a shallow 10–12-in (24.4–31 cm) pool of 30% magnesium sulfate (Epsom salt) solution.

The density of this solution provides the floater with complete buoyancy and weightlessness. Indeed, the solution’s density makes it impossible for the user to sink.

A float session begins when the tank’s door is closed. Light is completely eliminated and sound is reduced to near zero through the combination of the tank’s insulation and submersion of the floater’s ears.

Earplugs can further block outside noises. The air and water within the tank are maintained at a constant skin temperature. This neutral temperature prevents the physical and mental distractions caused by cold and heat.

The silky nature of the solution further reduces the separation between the floater’s skin and its surroundings, so that the body seems to gradually disappear. The combined elements of the tank, therefore, virtually eliminate all external stimulation for the floater.

Without environmental stimuli to process, the central nervous system’s level of activity drops dramatically, sending the floater into a state of deep relaxation.

The body undergoes positive physiological changes that work toward achieving homeostasis—the state of physical equilibrium. Muscular tension is released and proper blood flow is enhanced. Additionally, the body begins to balance any neurochemical imbalances caused by tension and stress.

There is increased production of endorphins and T-cells, which provide pain relief and increased immunity, respectively. In essence, relieved of outward stimuli, the floater’s central nervous system can concentrate most of its energies inward for the restoration of physical and mental health.

During a float session, the brain also enters the theta state, usually accessible only in the brief moments before falling asleep. This level of consciousness provides access to the right hemisphere of brain, which is associated with concentration, creativity, and learning. The brain can more easily retain information while in the theta state.

A typical float session lasts an hour, although longer sessions are available. After the floater rinses off the salt solution in a shower, most float centers provide a rest area to recuperate and reflect on the float session.

This downtime with other floaters and staff enhances the relaxation process. In total, the entire session lasts one-and-one-half to two hours. Repeated weekly sessions are suggested to achieve the full benefits of Floatation REST.


Getting ready for sensory deprivation
Getting ready for sensory deprivation

Persons interested in Flotation REST should consult with the local floatation center before the session. Most centers provide items such as towels, shampoo, soap, and hairdryers for their clients. Bathing suits are not required, and most people float without wearing one. It is recommended that a session be scheduled in advance to avoid a long wait.


People suffering from high blood pressure, heart disease, or kidney conditions should consult a physician or family doctor before undergoing Floatation REST. Those who have claustrophobia, certain psychological disorders, or discomfort in the dark may find the treatment unpleasant.

Side effects

Prolonged exposure to the Epsom salt solution may cause diarrhea and dry skin. Otherwise, Floatation REST has no known negative side effects.

Research and general acceptance

Unfortunately, sensory deprivation remains stigmatized by the general public. Many people continue to associate it negatively with the experiments conducted in the 1950s and 1960s. Science fiction movies such as Altered States have done little to improve the therapy’s public image.

For this reason, the term floatation REST is more accurately and commonly used. Floatation centers have begun appearing in cities throughout the world, and are growing in popularity. Studies confirming the positive physical and mental benefits of Floatation REST further enhance their popularity.

Floatation REST has been researched and studied for decades. The positive findings have impressed even those who were once strongly opposed to it. Journalist Michael Hutchinson tried to debunk the therapy but ended up writing what some call the “definitive” book on Floatation REST.

Hutchinson says in The Book of Floating that “there’s no doubt that floatation therapy works—as a therapeutic, educational, and entertainment tool, it has powerful effects on a number of levels, including the physical, emotional, intellectual, and spiritual.”

Research scientists and physicians confirm the benefits of floatation REST. In their study for Health Psychology, Jacobs and colleagues found that the results indicated that, “Floatation REST can be an effective means of teaching normal subjects to lower systolic and diastolic pressure and heighten their perception of relaxation.”

In their literature review, Floatation REST in Applied Psychophysiology, Drs. Thomas Fine and Roderick Borrie concluded that floatation REST can have positive psychophysiological effects and clinical applications as well as uses in pain management, performance enhancement, and the treatment of chronic illness and depression. Further studies support these findings.