A research expedition is under way which will see a small group of volunteers spend six weeks underground with no way of telling the time to study the impact on humans.

The 15-strong team, led by the French-Swiss explorer Christian Clot, entered the vast Lombrives cave complex in the Pyrenees mountains south of Toulouse on Sunday.

Those taking part in the extreme lockdown experiment, dubbed Deep Time, will remain in their subterranean home for 40 days, without phones, watches or natural light.

Prior to entering the cave, Mr Clot said: “Three separate living spaces have been set up: one for sleeping, one for living, and one for carrying out topography studies, in particular for fauna and flora.”

However, the main focus of the study will be the expedition leader and the seven men and seven women, aged 27 to 50, who have joined him underground where the temperature is a constant 12C (54F).

They have been fitted with sensors to allow monitoring by around a dozen scientists aiming to learn how humans react without the normal everyday frames of reference provided by time.

Etienne Koechlin, director of the cognitive neurosciences department at the Ecole Normale Superieur in Paris, who is part of the monitoring team, said: “This experiment is the first of its kind.

“Until now, these types of missions aimed to study the body’s physiological rhythms, but never the impact of this type of disconnection from time on a human being’s cognitive and emotional functions.”

The volunteers are drawn from across France and include a jeweller, an anaesthetist, a security guard and a steeplejack.

Four tons of provisions and other equipment have been stockpiled in the cave and so the group can live in complete isolation.

Fresh water will come from a well on site, and a bike-powered generator will provide electricity.

Arnaud Burel, a 29-year-old biologist, said he signed up “to experience this life removed from time, something that’s impossible to do on the outside with our computers and phones that are constantly reminding us of our appointments and obligations.”

“Forty days in your life, it’s just a drop in the ocean, isn’t it?” he said.

But he admitted: “It’s not easy to live with 14 people you don’t know, in a closed space – communication is going to be the key.”

Fortunately, the volunteers can leave at any time if the experience proves too much.

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