Researcher Kiana Aran Spent 5 Days in a Darkish Cave to Examine the Science of “Sensory Deprivation”

On a cold November day, Kiana Aran awoke to a surreal vision: Beyond a glass partition, she saw her mother, her cousin, and her grandmother—who had passed away years earlier—watching something on an iPad. Was it a dream or a hallucination? She could not tell; she didn’t even know if it was day or night. Aran, a bioengineering professor at University of California, San Diego was thousands of miles away from home, loaded with biosensors, and isolated in a dark cave to satisfy her quest for a calm mind and her scientific curiosity. And she was only about halfway into her five-day long experiment.

The idea of conducting a sensory-deprivation experiment upon herself took root in Aran’s mind after her paths crossed with a former venture capitalist Wojciech Ananda Jey (AJ) at a conference. AJ, who had once found himself caught in the loop of achievements and wants in life, had a profoundly positive and liberating experience in a dark cave in the wilderness. Thereafter, he set up a darkness cave retreat in Poland. When he invited Aran to try it, she was excited about the idea.

“As a faculty, my mind has been always racing. I have tried yoga, meditation to just calm my brain down, because I’m constantly thinking of, ‘Okay, what’s next, what’s next, what’s next.’ I cannot sit still, and sometimes it gets too much,” said Aran.

But while her human side was eager to dim her senses, the scientist in her could not resist leveraging sensors to turn her experience into an experiment. Aran saw this as an opportunity to test the effects of sensory deprivation on her body at a molecular and cellular level.¹

So began her preparation for the most personal experiment of her life.

A Modern Cave Woman Hunts for Data

While the term “sensory deprivation” is loosely used for a range of experiences, most setups only block visual and auditory stimuli. However, in the 1950s, sensory-deprivation experiments were much more literal: Individuals were devoid of all senses in a rather uncomfortable setup. Consequently, to avoid the negative connotation associated with the term “sensory deprivation,” psychologists introduced a more accurate term: reduced environmental stimulation therapy (REST). A dark, silent room set up—similar to the one that Aran would enter—is called Chamber-REST, while a high-salinity, shallow tank is termed Flotation-REST.²

In collaboration with her colleagues and a few other interdisciplinary scientists, Aran came up with an experimental design: They would monitor her biomarkers before, during, and after the darkness exposure to evaluate any changes in her body. Before entering the cave, the research team tested her cardiovascular health, bone density, muscle mass, blood biomarkers, microbiome, and mitochondrial function, among others. She planned to collect biosamples during her stay for comparative measurements. Aran also had Neuroverse sensors taped to her forehead to measure her brain activity, an Oura ring that tracked her sleep patterns and heart rate, and a glucose monitor to track any fluctuations due to circadian rhythm changes.

“I know these are studies that I can’t really make a conclusion, because it’s n of one. We have to do more. It was just interesting to observe how my body was responding,” said Aran.

In November 2024, strapped with sensors, armed with meditation exercises and training on how to handle hallucinations, and excited to try something new, Aran entered a cave chamber at “Within: The Ultimate Darkness Retreat” in Poland. For the next five days, she stayed isolated in a pitch-dark environment devoid of external sounds. She received one meal a day through a double window system to avoid light infiltration. Aran tracked the number of days by counting meals, but she soon lost track of day and night as the retreat team randomized her mealtimes.

Restless in the Chamber-REST

Overall, Aran found the Chamber-REST setup in the synthetic cave comfortable: She had a bed, a bathroom, and a shower. She acclimatized to her surroundings quickly and observed how her body adjusted to the new environment. Her eyes could “see” outlines in the dark, and she noticed her sense of taste heighten—the food flavors and textures felt more intense. Proteomic analysis of her saliva later validated that her taste receptor levels shot up within the first couple of hours in darkness.

Her post-experiment biomarker data analysis also revealed that the new environment triggered a heightened immune response, altered microbiome, and shifted circadian rhythms, but all parameters returned to baseline in a few days. At the time, her only challenges seemed to be collecting her biosamples in small tubes in the dark or ensuring that her sensors remained wrapped with duct tape to avoid light from leaking out (She found that even a small amount of light seemed bright in the dark cave).

But after a restful first day, her experiment turned into a test of mental resilience.

“I think it was when I received the second meal. After that, I was like, ‘How am I going to stay another three days here?’ Because I was doing nothing. For a person who’s constantly active, hour by hour, putting me in a room where I had nothing to do turned out to be a torture, sort of,” Aran confessed. “They had taught me meditation and breathing exercises, but I think by day three, day four, I just couldn’t wait to come out.”

Although Aran could have left the cave anytime, she felt compelled to complete her experiment for the sake of her colleagues. “I had people waiting for me outside…They were making sure that everything was working. So, I felt that I’m going to fail them if I come out.”

Justin Feinstein, a clinical neuropsychologist who met Aran after the experiment and heard her first-hand account of the experience, said, “I think she really did push herself.” He added, “She’s very courageous. She did this for science. She did this for her own self-exploration. But, you know, I couldn’t have done that.”

As multi-day sensory deprivation experiences gain popularity, Aran’s experiment raised a long outstanding question in the field of sensory deprivation and REST research: What’s the optimum number of days for such retreats? Psychologist Peter Suedland, professor emeritus at the University of British Columbia, who Feinstein referred to as the “grandfather of sensory deprivation research,” conducted Chamber-REST experiments in the 1970s in which participants would spend a day or two in a dark, silent room. “What he kind of told me is most of the effects, in his mind, were happening in that 24- to 48-hour window. And he didn’t necessarily think that extending it further was going to do anything different, but it hadn’t been fully tested,” said Feinstein.

He also noted another caveat. Healthy volunteers might not be the best representatives to test therapies designed to help people afflicted with mental health issues. An individual’s state of mind would make their tolerance limit and reaction to such experiences highly variable, so he advocates for a cautious approach when choosing the experience duration.

Aran hopes to secure funding to continue this work and find an answer for the optimal duration for such retreats. Meanwhile AJ’s team, in collaboration with an international team of researchers, is also planning a trial to test the effect of light deprivation on anxious patients using their setup.

Floatation-REST Therapy to Drown Stress and Anxiety

Feinstein, who was previously at the Laureate Institute for Brain Research, has extensively studied the effects of Floatation-REST on patients suffering from stress and anxiety disorders. In this setup, participants float in a shallow pool of water saturated with Epsom salt (magnesium sulfate) in a sound-proof, dark room for one to two hours. In his 2018 studies, Feinstein found that patients suffering from a range of anxiety and stress-related disorders self-reported reduced levels of stress and anxiety and showed a significant drop in their blood pressure after Flotation-REST sessions.^3,4

In humans, skeletal muscles in the back and those around the neck constantly harbor stress and anxiety, Feinstein explained. “In the float environment, all of that tension in your muscles—because you’re in a zero gravity-like state—dissipates.” Along with the skeletal muscle tension, the tension of the smooth muscles surrounding blood vessels and the cardiovascular system also dissipates, which is why the blood pressure lowers.

“One way to think of floating is it is sort of this automatic inducer of relaxation. It reduces all tension in the body and the mind. That’s very, very different than the experience Kiana went through because she’s sitting on things or standing on things. Gravity is pushing down on her literally every moment that she’s in that cave. You’re not getting that huge release of tension that you would expect in a float environment,” said Feinstein.

Curious about the effect of Flotation-REST on the brain, Feinstein and his team measured float-induced neural changes in participants in one study.⁵ “Right now, your brain’s probably firing 20 to 40 times a second. That’s the typical speed at which the brain is firing, but in the float environment it went down to one to two cycles a second.” According to him, this drop usually happens in states of deep non-REM sleep, yet they were seeing it in awake floaters. “It definitely was putting the nervous system into a very relaxed state; you could tell by the brain waves,” he said.

In 2021, Feinstein launched the non-profit Float Research Collective with a goal of making Flotation-REST an accepted form of drug-free therapy to alleviate anxiety and stress.

Take a Break, Find the Right REST

Whether it’s a darkness retreat or a flotation session, one of the goals of these programs is to provide people with natural, short-term alternatives to reduce medication dependency.

“Today, if you [are] a depressed patient or burnout patient, [your options are] heavy antidepressants, which are highly addictive, which numb you, which don’t solve the problem…or lengthy cognitive behavioral therapy, which is one or two or three years when you roll yourself in the mud of the past,” said AJ. “Imagine if we can prove that this short period of time can really make a difference.”

Feinstein added that the medication-overuse crisis is exacerbated by the short half-lives—four to eight hours—of addictive drugs like Xanax. Meanwhile their float therapy data shows significant anti-anxiety effects that last up to 48 hours post-session.⁶ Feinstein intends to conduct a study that goes “head-to-head against Xanax and really look at how long the effects last, how large of an anti-anxiety effect is in floating versus Xanax, and then really look at the physiological changes and differences as well, because I think this could be a complete replacement for this idea that the way to reduce anxiety is by popping pills.”

But REST is not just for patients; everyone could benefit from a break. “The elephant in the room with the society that we’re currently living in is our nervous system is overstimulated. We’re in a world of 24×7 connectivity, said Feinstein. “Part of the idea behind floating, the idea behind these darkness retreats, is just to give your nervous system a chance to break free of all this stimulation and just to give it a chance to actually rest.”

The right REST format might vary per individual, but Feinstein noted an important mindset detail that participants should internalize before trying anything: They are in complete control the whole time. “When people hear about any sort of environment, whether it’s a cave or a float tank or anything that might be enclosed, the first thought that comes to mind is, ‘I’m stuck. I’m trapped. I can’t get out.’ That’s not the case in all of these situations.”

Another important aspect is to know when to stop. “If you’re finding that your nervous system is not comfortable in that environment, don’t push yourself. Do it in a graded way,” said Feinstein. Aran, who despite the challenges of her experience finds value in REST therapies and has since tried Flotation-REST, agreed. She cited her own example, noting that she finds floating relaxing for about an hour but aggravating for longer periods. She is working on gradually building up her tolerance.

Interestingly, while Aran’s sensor data revealed temporary biomarker fluctuations, she sensed a permanent shift in her behavioral traits. She noticed an enhanced sense of gratitude, increased patience, and higher compassion levels (measured through an NIH-designed questionnaire). “I still carry [that feeling] with me,” she said. “Every time I get upset with something, I remember the darkness, and I’m like, ‘No.’ I appreciate everything I have right now all around me.”