In 1965, scientists wanted to study the psychological and physiological effects of isolation on humans, so they found two volunteers—a midwife named Josie Laures and a furniture maker named Antoine Senni—and left them alone in two separate caves in the French Alps for several months.

When Laures finally emerged from isolation 88 days later, after setting a world record, she thought it was February 25. It was March 12.

When Senni emerged after his record-setting 126 days, he thought it was February 4. It was April 5. 

After months in complete isolation, and without any sunlight to indicate time of day, both cave dwellers had lost track of entire weeks. Though scientists reported that both volunteers were physically and mentally healthy, their sleep patterns, and perceptions of time, were altered drastically during their time in the caves. 

In their recent story on the cave dwellers, The Atlantic explains, “Absent any cues from sunlight or even from clocks, Laures’s and Senni’s sleep schedules got wacky—sometimes without them realizing it.” Senna, for instance, would sometimes fall asleep for 30 hours at a time, and wake up thinking he’d just had a short nap. Scientists later discovered that, isolated from temporal cues, humans tend to slip into 48-hour sleep cycles—making it even harder to keep track of time.

Though both volunteers survived their ordeal, they admitted it wasn’t a particularly fun time. After emerging from her cave, Laures told the Associated Press

I am so happy to have lasted it out, that I have forgotten everything. I can tell you though that it became very difficult toward the end and I felt terribly worn out … At the start of my stay I read, and then I lost the desire. I didn't suffer from the cold. I was well heated in my little tent. My tape recorder refused to work the first few days, but later I managed to repair it and I listened to music. Outside of that I knitted, and knitted some more, and looked forward to the time when I would finally see the sun.

Check out the full story at The Atlantic to learn more about Laures and Senni's surreal experience.

[h/t: The Atlantic]