Here’s a thing I’ve learned through all the reading I’ve been doing about floating: the body has a relaxation response as the physiological counterpart to the fight-or-flight response. I was surprised — I hadn’t heard of this before — and then that thought was almost instantly followed by “of course it does”.
Fight-or-flight is well known, and had been extensively studied for almost a century. The body responds to perceived threat or danger with a reflex that releases hormones like adrenalin and cortisol, speeding the heart rate, slowing digestion, shunting blood flow to major muscle groups, and changing various other autonomic nervous functions. This gives the body a burst of energy and strength to defend ourselves under physical attack.
The shifts triggered by the adrenalin and cortisol are hard on the body — they’re supposed to be an emergency reaction, not the normal state of being. The body expects that after running or fighting, we’ll stop and rest and relax, giving it a chance to clean up. But unfortunately for us, the modern world frequently supplies stressful situations that trigger fight-or-flight where neither fight nor flight is a reasonable response, and where we also don’t get a clear time to stop.
What is the relaxation response? It is associated with instantly occurring physiological changes that quieten the sympathetic nervous system, reduce metabolism, and lower heart rate, blood pressure, and respiratory rate. A study just published by a group at Massachusetts General  has identified some of the biochemical processes involved: in particular, pathways involved with energy metabolism, particularly the function of mitochondria, were upregulated during the relaxation response. Pathways controlled by activation of a protein called NF-κB — known to have a prominent role in inflammation, stress, trauma and cancer — were suppressed, and the expression of genes involved in insulin pathways was also significantly altered.
At the psychological level, individuals typically experience the relaxation response as genuine rest, recovery, better sleep quality, less need for alcohol and psychoactive medication, as well as an increased sense of control and efficacy in stressful situations.
There are many techniques designed to try to elicit the relaxation response, including ones such as yoga and meditation derived from centuries of spiritual practice. The trick is, as Sven-Åke Bood puts it, “For a technique successfully to elicit the relaxation response, at least two main factors are necessary …, reduced sensory input and reduced bodily movements. A problem is that … the individuals in most need of relaxation techniques are often those who find it most difficult to initiate [these] relaxation exercises.”
Reduced sensory input and reduced bodily movement are of course what float tanks are all about. In the paper on stress-related pain I was reading yesterday, Bood’s group took some effort to try to detect the relaxation response. Specifically, they used a questionnaire called the “Experienced Deviation from Normal State” (EDN) instrument as a measure of altered states of consciousness. Previous studies have shown a connection between altered states and direct relaxation techniques like qigong, tai chi, and muscle relaxation training.
Sample questions on the EDN include: “I saw scenes rolling by like in a film“, “I could hear sounds without knowing where they came from“, and “Perception of time and space was like in a dream,” and the answers were marked between zero (“no, not more than usual”) and 100 (“yes, much more than usual”). A score of zero, then, means business totally as usual, while 100 is the maximum possible strangeness. For comparison, scores of 5 or less are “pretty normal”, while a guided shamanic drumming session can produce scores of 35. Bood et al measured their first-time floaters at 29.5, and the same people after their twelfth session at 40.1 EDN points. The tank, it’s strange in there.
 Manoj K. Bhasin, Jeffery A. Dusek, Bei-Hung Chang, Marie G. Joseph, John W. Denninger, Gregory L. Fricchione, Herbert Benson, Towia A. Libermann. “Relaxation Response Induces Temporal Transcriptome Changes in Energy Metabolism, Insulin Secretion and Inflammatory Pathways”, PLoS ONE, 2013; 8 (5): e62817 DOI: 10.1371/journal.pone.0062817
 Bood et al, “Eliciting the Relaxation Response With the Help of Flotation REST in Patients with Stress-related Ailments”, International Journal of Stress Management 2006, Vol. 13, No. 2, 154–175
 Kjellgren & Eriksson, “Altered States During Shamanic Drumming: A Phenomenological Study“, International Journal of Transpersonal Studies, 28, 2009, pp. 112-118.