Abstract

Floatation-REST (Reduced Environmental Stimulation Therapy) reduces sensory input to the nervous system through the act of floating supine in a pool of water saturated with Epsom salt. The float experience is calibrated so that sensory signals from visual, auditory, olfactory, gustatory, thermal, tactile, vestibular, gravitational and proprioceptive channels are minimized, as is most movement and speech. This open-label study aimed to examine whether Floatation-REST would attenuate symptoms of anxiety, stress, and depression in a clinical sample. Fifty participants were recruited across a spectrum of anxiety and stress-related disorders (posttraumatic stress, generalized anxiety, panic, agoraphobia, and social anxiety), most (n = 46) with comorbid unipolar depression. Measures of self-reported affect were collected immediately before and after a 1-hour float session, with the primary outcome measure being the pre- to post-float change score on the Spielberger State Anxiety Inventory. Irrespective of diagnosis, Floatation-REST substantially reduced state anxiety (estimated Cohen’s d > 2). Moreover, participants reported significant reductions in stress, muscle tension, pain, depression and negative affect, accompanied by a significant improvement in mood characterized by increases in serenity, relaxation, happiness and overall well-being (p < .0001 for all variables). In reference to a group of 30 non-anxious participants, the effects were found to be more robust in the anxious sample and approaching non-anxious levels during the post-float period. Further analysis revealed that the most severely anxious participants reported the largest effects. Overall, the procedure was well-tolerated, with no major safety concerns stemming from this single session. The findings from this initial study need to be replicated in larger controlled trials, but suggest that Floatation-REST may be a promising technique for transiently reducing the suffering in those with anxiety and depression.

Introduction

The history of Floatation-REST dates back to the 1950’s when Drs. Jay Shurley and John Lilly at the National Institute of Mental Health became interested in understanding how the human brain would respond to an environment devoid of external sensory input. It was discovered that rather than falling into a deep sleep or losing consciousness, participants maintained full awareness [1, 2]. Initial designs employed various masks intended to shield the brain from sensory input [1], whereas the first fully immersive floatation tank wasn’t built until 1957, when Dr. Shurley constructed his laboratory at the Oklahoma City Veterans Administration hospital [2]. In this first iteration of Floatation-REST, the participant was immersed vertically in a tank of water with an opaque helmet surrounding their head connected to a series of breathing tubes for ventilation. Due to the confined nature of the helmet, very few individuals participated in these early experiments outside of NASA astronauts in training for the mission to the moon [3, 4].

In the 1970’s, Glenn Perry (in collaboration with John Lilly) invented a horizontal version of the float tank that removed the need to wear a helmet [5]. This newer iteration has individuals lay supine in a shallow pool of water saturated with a high concentration of Epsom salt, allowing individuals to effortlessly float on their back, with the eyes, nose, and mouth comfortably hovering above the water surface. While this change in design exposed floating to a much wider audience, many still found the tanks too confining and claustrophobic in nature. Consequently, floating went through a long period of dormancy up until this past decade, where the practice has witnessed a rapid rise in popularity, likely bolstered by the creation of more spacious tanks and pools. Hundreds of commercial “float centers” have started to open across North America and Europe, where individuals will pay money to float, with sessions typically ranging between 45–90 minutes in duration.

Despite this recent surge in float centers, there has been very little research investigating Floatation-REST. The majority of past floatation research occurred in the 1980’s and 1990’s, primarily in small samples of healthy participants. The most consistent observation to date has been significant reductions in levels of subjective stress and increases in relaxation as measured from pre- to post-float [6–12]. Concomitant with these subjective findings, floating has also been reported to decrease blood pressure [12–17], heart rate [11, 13], as well as plasma cortisol [17–19]; but see [20]. A meta-analysis of 27 Floatation-REST studies found a large overall effect size for stress reduction [21], with most studies focused exclusively on healthy populations.

Clinical research investigating Floatation-REST, although limited, has reported largely beneficial effects across a range of different stress-related conditions, including: hypertension [14, 16], chronic tension headaches [22, 23], chronic muscle tension pain in the back and neck [24], and stress-related pain with “burnout depression” [7, 25]. Thus far there have only been two published Floatation-REST studies focused on individuals with anxiety [23, 26], both in participants with self-reported symptoms of “generalized anxiety." These studies examined the long-term effects of repeated float sessions, but did not assess the short-term effects arising from a single float session. The first study [23] was an uncontrolled investigation at a hospital that collected retrospective surveys in patients who utilized their Floatation-REST facility as part of a stress management program. They found that after ~7 float sessions, patients with generalized anxiety reported improvement in symptoms when assessed an average of 7 months later. The second study [26], a pilot trial in 50 participants randomized to either a waitlist control group or 12 sessions of Floatation-REST, observed a significant reduction in symptoms of generalized anxiety in the float group that was maintained at 6-month follow-up. No studies to date have examined the effects of Floatation-REST in posttraumatic stress disorder (PTSD), panic disorder, agoraphobia, social anxiety disorder, or major depressive disorder, and with the exception of a few individual case studies [27, 28], there has been no other research investigating the impact of Floatation-REST in patients with clinically diagnosed anxiety, depression, or any other mental health disorder.

Anxiety and depression are the two most common mental health disorders, with the proportion of people who will develop a disorder at some point in life (i.e., lifetime morbid risk) estimated to be 42% for anxiety disorders and 30% for major depression [29]. While viewed as separate conditions, comorbidity is often the rule rather than exception, with well over 50% of cases displaying a mix of both anxiety and depression [30, 31]. The cost and toll to society is tremendous, with depression now considered to be the leading cause of worldwide disability [32, 33], and anxiety the sixth leading cause of worldwide disability [34]. The age of onset is typically in adolescence and young adulthood, with symptoms often persisting throughout life without treatment [29, 35, 36]. Pharmacotherapy (e.g., selective serotonin reuptake inhibitor) and psychotherapy (e.g., cognitive behavioral therapy) are the two most commonly prescribed treatments for both anxiety and depression [37, 38]. Recent meta-analyses and large-scale clinical trials suggest that approximately 50% of patients improve with treatment [39, 40], with substantially poorer outcomes and adherence in patients with comorbid anxiety and depression [41, 42]. Given the insufficient treatment response and adherence to currently available therapies, it is important to explore novel ways of helping patients with anxiety and depression.

While the extant research (reviewed above) suggests that Floatation-REST may be a useful technique for stress reduction, there has been essentially no research exploring whether its stress-reducing properties can be effectively applied to individuals with clinically-diagnosed anxiety and depression. Consequently, this study took a transdiagnostic approach by recruiting a heterogeneous sample spanning the spectrum of different anxiety and stress-related disorders including PTSD, Generalized Anxiety Disorder, Panic Disorder, Agoraphobia, and Social Anxiety Disorder, as well as comorbid unipolar Major Depression. Since this was the first Floatation-REST study to examine these different clinical disorders, close attention was paid to issues of safety and tolerability. We were also interested in characterizing the range of different emotional and subjective changes that might arise in this environment, to detect whether any clinically meaningful changes were being induced. We hypothesized that a single session of Floatation-REST would lead to an acute reduction in symptoms of anxiety and depression irrespective of diagnosis.

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Discussion

This study found that a single one-hour session of Floatation-REST was capable of inducing a strong reduction in state anxiety and a substantial improvement in mood in a group of 50 anxious and depressed participants spanning a range of different anxiety and stress-related disorders (including PTSD, Generalized Anxiety Disorder, Panic Disorder, Agoraphobia, and Social Anxiety Disorder). The findings from this open-label study suggest that Floatation-REST may be a promising technique for acutely reducing symptoms of anxiety and depression, although the persistence of these effects is presently unknown. With regard to our primary outcome measure, the reduction in state anxiety was evident in every participant regardless of sex or medication status (Fig 4A). Moreover, the anxiety reduction was robust, with an estimated Cohen’s d > 2 across all disorders and subgroups (S3 Fig). Beyond the immediate dissipation of anxiety, the float experience also induced a significant decrease (p < .0001) in self-reported stress, muscle tension, pain, depression, and negative affect, along with a significant increase (p < .0001) in serenity, relaxation, happiness, positive affect, overall well-being, energy levels, and feeling refreshed, content and peaceful (Fig 5), with estimated effect sizes ranging from large to very large across variables (Fig 6).

On key symptom-related variables—such as reductions in state anxiety, stress, depression, and negative affect—the effect sizes were consistently large across all tested diagnostic categories (S3 Fig). An exploratory subgroup analysis revealed that those with the most severe anxiety reported the largest effects (S4 Fig). This latter finding is notable given the fact that the severely anxious participants reported having the most severe impairments in life functioning (Table 2), and also tended to be the most resistant to other forms of treatment; approximately two-thirds of the severely anxious participants were currently taking an SSRI or SNRI, and over three-quarters had tried psychotherapy. Indeed, most participants in this study reported having tried a number of other techniques to help them relax and feel less anxious and stressed (S5 Fig). Of potential clinical relevance, nearly 75% of the entire sample, and 82% of the severely anxious subgroup, reported that they had achieved more relaxation with Floatation-REST than any of the other treatments or techniques they had tried in the past (S5 Fig). While demand characteristics, expectancy effects, novelty effects, and retrospective recall biases may be inflating these subjective comparisons with other therapeutic modalities, the debriefing interviews (S1 Debriefing interview transcriptions) revealed that the float experience had a powerful positive effect on many of the participants. In future studies, it will be important to assess whether such positive effects can be maintained, or even further improved, with repeated sessions of Floatation-REST.

In comparison to previous float studies [21], the effect sizes observed in our anxious and depressed sample were about twice as large. Since many of the previous studies tested healthy participants, this noted disparity in effects may be driven by the possibility that Floatation-REST provides the largest effect to those who bring the most stress into the float experience. Such an interpretation is consistent with the larger float-induced changes observed in the severely anxious subgroup (S4 Fig), and the relatively small float-induced changes observed in the non-anxious reference sample (S2 Fig). While this study was not designed to directly compare anxious to healthy samples, the limited data we have on this matter suggests that Floatation-REST may temporarily lower state anxiety to near-normal levels (Fig 4B).

Although mood and anxiety disorders are heterogeneous in terms of their diversity of symptoms and emotional triggers, recent efforts have attempted to develop more effective treatments that can work in a transdiagnostic manner [74–76]. Transdiagnostic treatments have the obvious advantage of being easier to disseminate and more widely applicable, especially given the high rate of comorbidity between the different mood and anxiety disorders. To our knowledge, this is the first Floatation-REST trial in individuals across the spectrum of anxiety and depression, with results showing clear signs of short-term benefit in PTSD, Generalized Anxiety Disorder, Panic Disorder, Agoraphobia, Social Anxiety Disorder, and Major Depression. Previous float research with psychiatric populations did not assess the short-term effects following a single float session, but did assess the long-term effects (up to 6 months post-treatment) following 12 float sessions, and found evidence for sustained long-term benefit in individuals with generalized anxiety [26] or burnout depression [7, 25]. Together, these findings suggest that Floatation-REST may have the potential to be a viable transdiagnostic therapy for relieving symptoms of anxiety and depression.

Anxiety and depression affect over a quarter of the population, yet more than three-quarters of patients never receive treatment [35, 77]. This utilization problem is even worse in patients with social phobia [78, 79] or multiple comorbidities [77, 78, 80]. Novel non-pharmacological therapies for anxiety and depression are desperately needed, and the promising results of this initial Floatation-REST trial warrant further investigation, especially given the insufficient response rates and adherence to currently available treatments [39–42], and the paucity of novel medications reaching market over the past two decades [38]. In addition, many medications come with a host of side effects, which further contributes to the poor rates of adherence. The barriers to treatment utilization are complicated, but one of the most common reasons why patients with mood and anxiety disorders fail to receive treatment is due to the notion that they want to solve the problem on their own [81]. In this regard, Floatation-REST may offer an attractive alternative option that enhances self-efficacy and improves treatment utilization by providing anxious patients with the opportunity to learn new ways of coping with distress on their own. In addition, Floatation-REST appeared to be well-tolerated by this sample, with minimal evidence of harm, adverse events or major safety concerns arising during the initial float session. Positive experiences outweighed all negative experiences, and consequently, 96% of the participants chose to float for the entire hour, and 100% of the participants requested to float again. The non-pharmacological nature of Floatation-REST, combined with its lack of side effects, ease of use, and rapid onset of benefit, are additional positive attributes that may further improve treatment utilization and adherence.

A note on “sensory deprivation”

In contrast to the prevailing positive experience reported post-float, there were clear signs of pre-float anticipatory anxiety and avoidance behavior. Fifteen participants failed to show for their scheduled appointment and never rescheduled (Fig 1), and another fifteen participants called to reschedule their appointment, often at the last minute. While it is not uncommon for anxious individuals to avoid novel experiences, it is worth noting the heightened anticipatory anxiety that anxious patients may have about Floatation-REST, as this creates a clear barrier to entry. One potential reason for the anticipatory anxiety of Floatation-REST may stem from its association with “sensory deprivation”, a loaded term which engenders many historical, and often incorrect, stereotypes related to a loss of control, hallucinations, paranoia and panic [82, 83]. The relaxing and serene state induced by Floatation-REST in the current study appears to be very different (in fact, polar opposite) to the unpleasant and anxious states that were sometimes reported in sensory deprivation research from the 1950’s that did not involve floating in a pool of water [82, 83]. Similarly, Chamber-REST research, which has participants lie in a dark sound-attenuated room, has also found a general lack of negative effects induced by the experience, even in experiments lasting 24 hours in duration, whereas positive benefits of Chamber-REST have been observed across a number of conditions including autism, smoking addiction, and even snake phobia [27]. Given the striking discrepancy between the positive effects found in modern day REST research and negative effects found in early sensory deprivation research, the term sensory deprivation has largely been replaced by restricted environmental stimulation therapy (“REST”) [82]. We strongly agree with this replacement, as it helps to avoid confusion and steer clear of historical stereotypes that may heighten the barrier to entry for anxious populations. In this paper, we refer to the first term in the REST acronym as “reduced” instead of the more commonly used term of “restricted” in order to further minimize any potential negative associations that may be elicited by this latter term.

Considerations for replication

As mentioned in the Introduction, there are now hundreds of recreational float centers (http://floatationlocations.com/where-to-float/) where consumers can pay money to float, typically ranging between $40-$100 per session. It is not yet clear whether the anxiety reducing effects found in the different clinical populations studied here can be fully replicated in recreational facilities. In contrast to the open pool design employed in this study, most recreational facilities have enclosed floatation tanks. Enclosed tanks may heighten the anxiety in patients, especially if they have any claustrophobia. In addition, many enclosed tanks fail to ventilate the air near the surface of the water, allowing for the build-up of high levels of humidity and carbon dioxide, which can further heighten anxiety.

Additional precautions were also taken to provide participants with complete control over the float experience, including having the ability to turn the lights on or off using an infrared wave detection system. In contrast, many float centers do not offer this option, and some float tanks do not even have a light. Likewise, all participants in this study received a thorough introduction prior to their float experience by a mental health professional, and were continuously monitored throughout the experience using an intercom system. These factors may have increased the participants’ overall level of safety and comfort, and may have also diminished the base rate of adverse events. Thus, the optimized setting created in this study may have contributed to the positive results.

Limitations & future directions

Although the findings from this initial study provide early indications for a clinically meaningful signal in anxious and depressed individuals, many important questions remain. The study was limited by its open-label design and lack of a control group. Moreover, since this was only a single-float study, it will be imperative for future studies to explore the effects of multiple float sessions to determine whether there is any evidence for sustained long-term benefit or any sign of adverse effects from repeated sessions. In addition, no studies have examined how long the acute effects persist after a float is over, and a better understanding for the duration of the acute effects will be important prior to determining other factors such as the optimal “dose” of floating. It will be incumbent upon future research to explore how long the benefits last after a single float session, and whether the persistence of such effects changes following multiple float sessions. Replication using a randomized controlled design with longitudinal follow-up will be a critical step for assessing the efficacy of Floatation-REST in anxious and depressed populations. It will also be important to identify a good comparator condition that controls for the effects of expectation and assesses the degree to which the relaxation benefits can be obtained in a setting outside of the float pool. Notably, the selection of a comparator should be based on the specific hypothesis and there is unlikely to be a “one size fits all” solution as the specific target of treatment could change based on the clinical population under investigation. The current investigation targeted state anxiety, and the findings revealed that the reduction of state anxiety was consistently the largest effect across all subgroups and diagnostic categories (S3 Fig), highlighting this metric as a useful target for future investigations.

Despite over a half-century of investigation, the science of Floatation-REST is still in its very early stages. Given the large number of sensory systems altered by the float experience, it is currently unclear what factors are driving the positive effects. Culturally speaking, modern society is in the midst of a technological renaissance that has created a near constant state of connectivity. Addiction to social media and technology has become rampant [84], making it increasingly difficult to unplug for even a single day [85]. And while many find the prospect of being alone and doing nothing for even a short period of time to be aversive [86], the current results suggest that occasionally ‘disconnecting’ from technology and providing the nervous system with a respite from outside stimulation might actually be conducive for mental health. Beyond the potential mental benefits, Floatation-REST also seems to provide clear physical benefits, as our data revealed large reductions in muscle tension and pain, with muscle tension showing the largest reduction out of all the measures (Fig 5). Since the body can harbor stress [87], often in the form of muscle tension and pain, it remains possible that many of the positive benefits derived from Floatation-REST are being driven through the body-based nature of the intervention. Reductions in somatomotor activity and exteroceptive sensory input may also play a role in the positive benefits, but it is currently difficult to discern the precise extent. For example, having the lights off during the float session provided some advantages (in terms of effect size) on measures of serenity, well-being, stress, and negative affect, but it did not alter the overall level of state anxiety reduction, which remained high regardless of whether the lights were on or off. Thus, it seems plausible that the clinical impact of Floatation-REST could be a byproduct or summation of all the different sensory and motor systems that are altered by the float experience, rather than any single system driving the change by itself. Many possibilities exist and future research will need to decipher how floating affects the nervous system in order to isolate the active ingredients.