Kiana Aran spent five days in one of several cave-like chambers built into hills in western Poland.Credit: Kinga Janowska and Wojciech Ananda Jay founders of Darkness Cave Retreat
In the cold of November, in a quiet corner of Poland, I entered a cave with nothing but myself and a suite of biosensors.
As a scientist and engineer at the University of California, San Diego, my goal has always been to create technologies that can seamlessly translate the hidden language of our biology — data that are often messy, high-dimensional and difficult to interpret — into precise, reliable signals that can be used for health monitoring.
Nature Spotlight: Sensors
When the opportunity arose in November 2024 to take part in a prolonged sensory-deprivation experience in a darkness retreat cave in rural Wróblewo, west central Poland, I saw it as a chance to experiment. I had long been curious about how my daily routines, food choices and stress levels influenced my biology and had casually tracked myself with sensors such as a glucose monitor and the Oura Ring, which measures factors such as sleep quality and body temperature. But the cave offered something different: the total removal of external stimuli.
Five days in complete darkness and silence where no light, sound or time cues could reach me. I was physically alone and my activities became a series of improvized rituals: eating slowly so I could savour the only sensory input I had, stretching to release tension, reviewing memories and sometimes simply sitting and listening to my own heartbeat.
To capture the biological impact of this extreme environment, I used a comprehensive suite of sensors and biomarker analyses. I wore a wireless electroencephalograph (EEG) system to monitor brain activity, sleep stages and neural signatures of stress and adaptation; the Oura Ring to continuously track sleep patterns, heart-rate variability and circadian-rhythm shifts; and the glucose monitor to follow metabolic responses in real time.
Real-time molecular recorders expose the inner lives of cells
I also collected extensive multi-omics data before, during and after the cave experience, including blood proteomics to measure changes in my metabolism, immune responsiveness and stress signalling and stool, saliva, skin and urine microbiome sequencing to understand shifts in my microbial ecology and body composition.
Because this experiment crossed so many scientific domains, I was fortunate to be surrounded by an extraordinary team at my university and beyond, who helped me to analyse the various data streams. Not only were my colleagues supportive, but many were also as intrigued and admittedly as nervous about the experiment as I was. The beauty of data is that they made my inner experience something I could share. I could show colleagues the changes in my sleep architecture, glucose curves, microbiome shifts. They couldn’t feel what I felt in the darkness, but they could see it. After days without light or time cues, the sensors and tests began to tell a coherent story of how the body recalibrates perception, metabolism and cellular function in isolation.
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