Michel Siffre, ‘chronobiologist’ who spent months alone underground to test his sanity

He emerged ‘a half-crazed, disjointed marionette’. He struggled to think, and took five minutes to count what he thought was 120 seconds

Michel Siffre, who has died aged 85, was a speleologist and self-styled “chronobiologist”, who conducted experiments to determine the effects of long periods of time spent underground and find out how much our sense of time is thrown out of kilter without external clues.
In 1961, aged 22, he discovered a rare underground glacier in the Scarasson Cavern of the Maritime Alps near Nice, and decided the following summer to descend into the cavern to study the glacier at close quarters.
In the meantime he had become fascinated by research into sleep patterns carried out by the US physiologist Nathaniel Kleitman and, as an afterthought, decided to put his own internal clock to the test.
“This idea came to me – this idea that became the idea of my life,” Siffre recalled. “I decided to live like an animal, without a watch, in the dark, without knowing the time.”
He spent 61 days in the cavern where, before going to sleep and just after waking, he would radio up to his support team, who kept a record of the times. Siffre’s body clock maintained an almost perfectly regular cycle even in the gloom of the cave. But, intriguingly, it lasted around 24 hours and 30 minutes.
Siffre himself, however, completely lost track of time. His teammates at ground level found that it took him more than five minutes to count what he thought was 120 seconds. When he eventually emerged on September 17, feeling like “a half-crazed, disjointed marionette”, he thought it was August 20. It seemed that although his body knew what was happening, his mind did not.
Long-term isolation, with or without time cues, had obvious implications for manned lunar bases and submarine crews, and 10 years later, working with Nasa, Siffre went into voluntary isolation again in a cave near Del Rio, Texas.
He remained there for 205 days – nearly seven months.
As on the previous occasion, he lost track of time, his estimates, when he emerged, being two months out. He also found that without time cues he seemed to have adjusted to a 48-hour rather than a 24-hour cycle.
This time, however, the effects on his brain were more serious. He reported resenting the tasks he had to perform, lapses of memory and concentration and a growing sense of panic. He began to fear the fungus that grew on the cave walls and became convinced he would catch diseases from the cave dust. And he became seriously depressed and so lonely that he tried to befriend a mouse. When he accidentally crushed and killed it, he wrote in his diary: “Desolation overwhelms me” and thought of taking his own life.
Although he had everything he needed to survive, without human company his mind began to break down. By the time he emerged he could only say a few words and he found it extremely difficult to think. Subsequently he moved away from his home in France and divorced his wife.
Nonetheless, in 1999, inspired by American astronaut John Glenn’s return to space at the age of 77, the 61-year-old Siffre decided to try again.
On November 30 he descended 2,970 feet into the Clamousse grotto, 20 miles north of Montpellier, with electrodes attached to his body to enable scientists at the National Institute of Space Studies to measure his heartbeat, breathing and body temperature. He also agreed to take regular blood, saliva and urine samples to check if he was ageing more slowly than normal.
During his 76 days underground, he again lost track of time, celebrating Christmas on December 27 and the Millennium at 3pm on January 4. When he was hauled up he thought it was a week too soon.
Again his mind was affected. He kept forgetting to take blood and other tests. “I had the impression I had lost my memory. I couldn’t remember what I had been doing even hours earlier,” he recalled.
Michel Siffre was born in Nice on January 3 1939 and discovered a love of caving after being taken aged 10 to a cave park.
The Scarasson experiment changed Siffre’s life, turning him into a minor celebrity in France. From 1962 he conducted “out of time” experiments not only on himself but on volunteers.
His experiments added to scientific knowledge about biological rhythms and he gathered data showing that, as isolation lengthens to two, three and four months, some humans, himself included, adopt a 48-hour cycle. This conclusion was initially hotly contested by researchers, but was subsequently confirmed by the Americans Elliot Weitzman and Charles Czeisler.
But Siffre was sometimes accused of taking unnecessary risks in the search for publicity. In 1988 one of his guinea pigs, Veronique Le Guen, an attractive 32-year-old Parisienne, hoping to set a world record for the most time spent alone in an underground cavern by a woman, volunteered to live alone in the Valat-Negre cavern in south-central France without a clock for 111 days.
But in January 1990, 14 months after she re-emerged after breaking the record amid much razzamatazz, she was found dead in her car in Paris, having taken a high dose of barbiturates. Her husband claimed that, despite Siffre’s own experience in Texas, his wife had not been sufficiently warned of possible psychological side effects.
Siffre denied there was any connection between Veronique’s death and his experiment. “I never ask somebody to make an experiment. They choose themselves!” he declared. “They come to me. They ask me to make an experiment. And I transform their will to be known, to become glorious in scientific experiments. It’s very different, my approach. And it’s my strength, you know? It’s why we have always had a success. We have never had a failure in any of my experiments.”
Michel Siffre, born January 3 1939, died August 25 2024