What happens when humans spend too much time in the dark

Our aversion to darkness is rooted in our eyes. We are diurnal, active creatures of the day, that is to say that our ancestors, up to the finest physiological points, have been adapted to search, navigate and shelter. while the sun was rising. Of course, in the light of day, our eyes are beautiful. We have an abundance of photoreceptor cells called "cone cells" that allow us to address specific details: our ancestors could distinguish game on the horizon or see a fruit in a tree and know from color if it was ripe or no. But without the sunlight, our eyes are almost useless: for our intestine of conical cells, we lack the other type of photoreceptor, the "rod cells", which allow vision in low light. At sunset, every night, our ancestors became vulnerable and turned from predators into prey by entering a world dominated by nocturnal hunters, all with powerful night vision: lions, hyenas, saber-toothed tigers , venomous snakes. For our ancestors, the greatest terror would have swept the savannah in the dark, listening to the legs of a predator drumming against the ground.

In the modern West, we are no longer under the ambush of saber-toothed tigers, but we always bow in the dark. Annie Dillard wrote, "After thousands of years, we are still strangers to darkness, scary extraterrestrials in an enemy camp, arms folded on their chests." Darkness often worried me. In the sardine games of my childhood, hidden in a corner of my father's closet, my heart is pounding. In the bush in Australia, get up to pee without a flashlight, lose sight of the tent, stumble in the dark, think of packets of dingoes. After Hurricane Sandy in New York, crossing lower Manhattan, block after block of the blackened grid of the city, the hair spiked on the nape of the neck. But it was partial darkness, always with a point of light through a keyhole or a star glow of the sky. Here, the eye will always adjust, the iris will always open to collect photons. Not underground. In the dark of a cavity, not a single photon penetrates. Here lies a somber and dark old, dark in the Book of Genesis.

My thoughts wormed in my body, nibbling at my interior architecture. It was the feeling of being peeled, returned. I felt the rhythmic tightness of my heart, my lungs swell inside my ribs, my epiglottis opening and closing. In the absence of sight, my other senses have blossomed. The sound of the stream, which I had scarcely noticed when I entered the grotto, now filled the whole room, unfolding in effusive patterns. Odors – mud, wet limestone – thicken to the point of touching. I could taste the cave. When a drop of water fell from the ceiling and burst on my forehead, I almost jumped out of my sleeping bag.

Our first studies on sensory deprivation arose from a Cold War clandestine military experiment on mental control. In the early 1950s, images of American prisoners of war denouncing capitalism and extolling the virtues of communism emerged from Korea. The CIA, convinced that the soldiers had been brainwashed, quickly launched a research initiative – the Bluebird Project – on mind control techniques. One of the members of the research team was a psychologist, Donald Hebb, who had proposed an experiment on what he called "sensory isolation".

Hebb was not so interested in brainwashing, but was curious about how the brain reacted to the absence of stimuli. He wondered, for example, that pilots of the Royal Air Force, who, after many hours of flying alone and staring at the immutable line of horizon, would suddenly lose, for no apparent reason, the control of the aircraft. and plane and crash. And sailors who, after being stretched out on a static marine horizon, saw mirages. And among the Inuit who warned against fishing solo, because in the absence of human contact, without visual cues in a white arctic landscape, they would be disoriented and head for the sea, never to return. In examining the neurological response to isolation, Hebb wondered if he could perhaps answer questions about the structure of the brain.

For Project X-38, Hebb built a four by six by eight foot cell grid, each air-conditioned and soundproofed, then recruited volunteers, which he paid twenty dollars a day to lie in cells , The subjects wore frosted plastic goggles preventing "pattern vision". To reduce tactile stimulation, they wore cotton gloves and cardboard wrists at the elbows of the fingers. On their ears, a U-shaped foam pillow. The cells were equipped with observation windows and an intercom so that the research team could communicate with the subjects. Hebb asked his volunteers to stay in the cells as long as they could.

At first, Hebb had considered the X-38 project with a light heart, joking that the worst of the isolation for the subjects would be the meals prepared by his post-docs. When the results arrived, however, he was stunned: the subject's disorientation was far more extreme than he had imagined. Once the study was over, a volunteer drove from the laboratory car park and crashed. On several occasions, when the subjects took a break to relieve themselves, they lost themselves in the bathroom and had to call a researcher to help them find a way out.

The most hallucinating were the hallucinations. After only a few hours of isolation, almost all the subjects saw and felt things that were not there. They would first see bright spots and simple geometric patterns; These transformed into complex and isolated images floating around the room, which then evolved into complex and integrated scenes unfolding under the subject's eyes – "dreaming awake", as one participant described. One participant reported seeing a parade of squirrels parade "on purpose" through a snow-covered field, carrying snowshoes and backpacks, while another saw a tub guided by an old man wearing a metal helmet. In one particularly extreme case, a subject encountered a second version of himself in the room: he and his appearance began to mix, until he was no longer able to discern which . "It is one thing," writes Hebb, "to hear that the Chinese are brainwashed to their prisoners on the other side of the world; it's another thing to see, in your own lab, that just taking a few days off the usual bodily images, sounds, and bodily touches of a healthy university student can upset it, right up to the bottom: it can disrupt its personal identity.

Today, the neurological mechanism behind these reactions is more or less understood. At all times, our brain receives a torrent of sensory information – visual, auditory, tactile, and so on. We are so used to this stream of data that when it is cut, our brains essentially produce their own stimuli. He identifies his own models, combining any insufficient blip in the visual cortex with images stored in memory to create extremely vivid scenes, even disconnected from current reality. In 2007, during a particularly rewarding experiment, researchers from the Max Planck Institute for Brain Research collaborated with a German artist, Marietta Schwarz, who volunteered for 22 days to live with eyes blinded. Blindversuch (Blind Study), as his project called Schwarz, was part of a larger artistic project called Knowledge of Space, which included interviews with blind people about perception, the image, the Space and art. Schwarz was blindfolded in the lab, recording in a dictaphone a detailed diary in real time of everything that was going on in his brain. She has reported a range of hallucinations, including intricate abstract patterns, such as amoebae, yellow clouds and animal prints. The researchers used a fMRI scanner – functional magnetic resonance imaging, which tracks changes in blood flow in the brain – to track the neurological operations behind its hallucinations. Despite the complete lack of visual display, Schwarz's visual cortex lit up like a lantern, just as if she were blindfolded.

That is, in the world of her brain, hallucinations were as true and real as anything she could touch, taste, or smell.

Excerpt from UNDERGROUND: A Human History of the Worlds Under Our Feet, © 2018 by Will Hunt. Reprinted with permission of Spiegel & Grau.