When people are isolated from human contact, their mind can do some truly bizarre things, says Michael Bond. Why does this happen? Sarah Shourd’s mind began to slip after about two months into her incarceration. She heard phantom footsteps and flashing lights, and spent most of her day crouched on all fours, listening through a gap in the door.

That summer, the 32-year-old had been hiking with two friends in the mountains of Iraqi Kurdistan when they were arrested by Iranian troops after straying onto the border with Iran. Accused of spying, they were kept in solitary confinement in Evin prison in Tehran, each in their own tiny cell. She endured almost 10,000 hours with little human contact before she was freed. One of the most disturbing effects was the hallucinations.

“In the periphery of my vision, I began to see flashing lights, only to jerk my head around to find that nothing was there,” she wrote in the New York Times in 2011. “At one point, I heard someone screaming, and it wasn’t until I felt the hands of one of the friendlier guards on my face, trying to revive me, that I realised the screams were my own.”

We all want to be alone from time to time, to escape the demands of our colleagues or the hassle of crowds. But not alone alone. For most people, prolonged social isolation is all bad, particularly mentally. We know this not only from reports by people like Shourd who have experienced it first-hand, but also from psychological experiments on the effects of isolation and sensory deprivation, some of which had to be called off due to the extreme and bizarre reactions of those involved. Why does the mind unravel so spectacularly when we’re truly on our own, and is there any way to stop it?

We’ve known for a while that isolation is physically bad for us. Chronically lonely people have higher blood pressure, are more vulnerable to infection, and are also more likely to develop Alzheimer’s disease and dementia. Loneliness also interferes with a whole range of everyday functioning, such as sleep patterns, attention and logical and verbal reasoning.

The mechanisms behind these effects are still unclear, though what is known is that social isolation unleashes an extreme immune response – a cascade of stress hormones and inflammation. This may have been appropriate in our early ancestors, when being isolated from the group carried big physical risks, but for us the outcome is mostly harmful.

Yet some of the most profound effects of loneliness are on the mind. For starters, isolation messes with our sense of time. One of the strangest effects is the ‘time-shifting’ reported by those who have spent long periods living underground without daylight. In 1961, French geologist Michel Siffre led a two-week expedition to study an underground glacier beneath the French Alps and ended up staying two months, fascinated by how the darkness affected human biology. He decided to abandon his watch and “live like an animal”. While conducting tests with his team on the surface, they discovered it took him five minutes to count to what he thought was 120 seconds.

A similar pattern of ‘slowing time’ was reported by Maurizio Montalbini, a sociologist and caving enthusiast. In 1993, Montalbini spent 366 days in an underground cavern near Pesaro in Italy that had been designed with Nasa to simulate space missions, breaking his own world record for time spent underground. When he emerged, he was convinced only 219 days had passed. His sleep-wake cycles had almost doubled in length. Since then, researchers have found that in darkness most people eventually adjust to a 48-hour cycle: 36 hours of activity followed by 12 hours of sleep. The reasons are still unclear.

As well as their time-shifts, Siffre and Montalbini reported periods of mental instability too. But these experiences were nothing compared with the extreme reactions seen in notorious sensory deprivation experiments in the mid-20th Century.

In the 1950s and 1960s, China was rumoured to be using solitary confinement to “brainwash” American prisoners captured during the Korean War, and the US and Canadian governments were all too keen to try it out. Their defence departments funded a series of research programmes that might be considered ethically dubious today.

The most extensive took place at McGill University Medical Center in Montreal, led by the psychologist Donald Hebb. The McGill researchers invited paid volunteers – mainly college students – to spend days or weeks by themselves in sound-proof cubicles, deprived of meaningful human contact. Their aim was to reduce perceptual stimulation to a minimum, to see how their subjects would behave when almost nothing was happening.

They minimised what they could feel, see, hear and touch, fitting them with translucent visors, cotton gloves and cardboard cuffs extending beyond the fingertips. As Scientific American magazine reported at the time, they had them lie on U-shaped foam pillows to restrict noise, and set up a continuous hum of air-conditioning units to mask small sounds.

After only a few hours, the students became acutely restless. They started to crave stimulation, talking, singing or reciting poetry to themselves to break the monotony. Later, many of them became anxious or highly emotional. Their mental performance suffered too, struggling with arithmetic and word association tests.

But the most alarming effects were the hallucinations. They would start with points of light, lines or shapes, eventually evolving into bizarre scenes, such as squirrels marching with sacks over their shoulders or processions of eyeglasses filing down a street. They had no control over what they saw: one man saw only dogs; another, babies.

Some of them experienced sound hallucinations as well: a music box or a choir, for instance. Others imagined sensations of touch: one man had the sense he had been hit in the arm by pellets fired from guns. Another, reaching out to touch a doorknob, felt an electric shock. When they emerged from the experiment they found it hard to shake this altered sense of reality, convinced that the whole room was in motion, or that objects were constantly changing shape and size. Distressing end

The researchers had hoped to observe their subjects over several weeks, but the trial was cut short because they became too distressed to carry on. Few lasted beyond two days, and none as long as a week. Afterwards, Hebb wrote in the journal American Psychologist that the results were “very unsettling to us… It is one thing to hear that the Chinese are brainwashing their prisoners on the other side of the world; it is another to find, in your own laboratory, that merely taking away the usual sights, sounds, and bodily contacts from a healthy university student for a few days can shake him, right down to the base.”

In 2008, clinical psychologist Ian Robbins recreated Hebb’s experiment in collaboration with the BBC, isolating six volunteers for 48 hours in sound-proofed rooms in a former nuclear bunker. The results were similar. The volunteers suffered anxiety, extreme emotions, paranoia and significant deterioration in their mental functioning. They also hallucinated: a heap of 5,000 empty oyster shells; a snake; zebras; tiny cars; the room taking off; mosquitoes; fighter planes buzzing around.

Why does the perceptually deprived brain play such tricks? Cognitive psychologists believe that the part of the brain that deals with ongoing tasks, such as sensory perception, is accustomed to dealing with a large quantity of information, such as visual, auditory and other environmental cues.

But when there is a dearth of information, says Robbins, “the various nerve systems feeding in to the brain’s central processor are still firing off, but in a way that doesn’t make sense. So after a while the brain starts to make sense of them, to make them into a pattern.” It creates whole images out of partial ones. In other words, it tries to construct a reality from the scant signals available to it, yet it ends up building a fantasy world.

Such mental failures should perhaps not surprise us. For one thing, we know that other primates do not fare well in isolation. One of the most graphic examples is psychologist Harry Harlow’s experiments on rhesus macaque monkeys at the University of Wisconsin-Madison during the 1960s, in which he deprived them of social contact after birth for months or years.

They became, he observed, “enormously disturbed” even after 30 days, and after a year were “obliterated” socially, incapable of interaction of any kind. (A comparable social fracturing has been observed in humans: consider the children rescued from Romanian orphanages in the early 1990s, who after being almost entirely deprived of close social contact since birth grew up with serious behavioural and attachment issues.)

Secondly, we derive meaning from our emotional states largely through contact with others. Biologists believe that human emotions evolved because they aided co-operation among our early ancestors who benefited from living in groups.

Their primary function is social. With no one to mediate our feelings of fear, anger, anxiety and sadness and help us determine their appropriateness, before long they deliver us a distorted sense of self, a perceptual fracturing or a profound irrationality. It seems that left too much to ourselves, the very system that regulates our social living can overwhelm us.

Take the 25,000 inmates held in “super-maximum security” prisons in the US today. Without social interaction, supermax prisoners have no way to test the appropriateness of their emotions or their fantastical thinking, says Terry Kupers, a forensic psychiatrist at the Wright Institute in Berkeley, California, who has interviewed thousands of supermax prisoners.

This is one of the reasons many suffer anxiety, paranoia and obsessive thoughts. Craig Haney, a psychologist at the University of California, Santa Cruz, and a leading authority on the mental health of inmates in the US, believes that some of them purposefully initiate brutal confrontations with prison staff just to reaffirm their own existence – to remember who they are. Coping strategy

Social isolation is not always debilitating, however. Are some better than others at coping? And can you train yourself to resist the worst effects? Here scientists have fewer hard answers, but we can at least look to the lessons of individuals who thrived – or floundered – under isolation.

When Shourd was imprisoned in Iran, she was arguably among the least-equipped people to cope, because her incarceration came out of the blue. People in her circumstances have their world suddenly inverted, and there is nothing in the manner of their taking – no narrative of sacrifice, or enduring for a greater good – to help them derive meaning from it. They must somehow find meaning in their predicament – or mentally detach themselves from their day-to-day reality, which is a monumental task when alone.

Hussain Al-Shahristani managed it. He was Saddam Hussein’s chief nuclear adviser before he was tortured and shut away in Abu Ghraib prison near Baghdad after refusing on moral grounds to cooperate on the development of an atomic weapon. He kept his sanity during 10 years of solitary confinement by taking refuge in a world of abstractions, making up mathematical problems which he then tried to solve.

He is now deputy energy minister of Iraq. Edith Bone, a medical academic and translator, followed a similar strategy during the seven years she spent imprisoned by the Hungarian communist government after World War Two, constructing an abacus out of stale bread and counting out an inventory of her vocabulary in the six languages she spoke fluently.

Such experiences may be easier to take if you belong to a military organisation. Keron Fletcher, a consultant psychiatrist who has helped debrief and treat hostages, says mock detention and interrogation exercises of the kind he himself underwent while serving with the Royal Air Force are a good preparation for the shock of capture. “They teach you the basics of coping,” he says. “Also, you know your buddies will be busting a gut to get you back in one piece. I think the military are less likely to feel helpless or hopeless. Hopelessness and helplessness are horrible things to live with and they erode morale and coping ability.”

US senator John McCain is a good example of how a military mindset bestows psychological advantages. His five-and-a-half years as a prisoner of war in Vietnam, during which he refused to yield to his interrogators, actually seemed to strengthen him. Though note what he had to say about the two years he spent in isolation: “It’s an awful thing, solitary. It crushes your spirit and weakens your resistance more effectively than any other form of mistreatment… The onset of despair is immediate, and it is a formidable foe.”

Extreme reality Psychologists who study how people cope with isolation have learnt much from solo explorers and mountaineers. For many adventurers deprived of human company – albeit voluntarily – the landscape itself can serve as an effective surrogate, drawing them out of themselves into the beauty or grandeur of their surroundings. Norwegian psychologist Gro Sandal at the University of Bergen in Norway, who has interviewed many adventurers about how they cope in extreme environments, says that transcending the reality of their situation in this way is a common coping mechanism. “It makes them feel safer. It makes them feel less alone.”

A similar psychological mechanism could explain why shipwrecked mariners marooned on islands have been known to anthropomorphise inanimate objects, in some cases creating a cabal of imaginary companions with whom to share the solitude. It sounds like madness but is likely a foil against it. Take the way sailor Ellen MacArthur nicknamed her trimaran “Mobi”, during her record-breaking solo circumnavigation of the globe in 2005. During the voyage she signed emails to her support team “love e and mobi”, and in her published account uses “we” rather than “I”.

There is no more poignant illustration of the power of solitude to sink one person while lifting up another than the stories of Bernard Moitessier and Donald Crowhurst, two of the competitors in the 1968 Sunday Times Golden Globe round-the-world yacht race.

The trophy, offered to the first sailor to complete a solo non-stop circumnavigation of the globe, was won in 313 days by Robin Knox-Johnston, the only one out of nine starters to finish. He seemed to relish being alone with his boat, but not as much as Moitessier, an ascetic Frenchman who practised yoga on deck and fed cheese to the shearwater birds that shadowed him.

Moitessier found the experience so fulfilling, and the idea of returning to civilisation so distasteful, that he abandoned the race despite a good chance of victory and just kept on sailing, eventually landing in Tahiti after travelling more than halfway round the world again. “I continue non-stop because I am happy at sea,” he declared, “and perhaps because I want to save my soul.”

Crowhurst, meanwhile, was in trouble from the start. He left England ill-prepared and sent fake reports about his supposed progress through the southern seas while never actually leaving the Atlantic. Drifting aimlessly for months off the coast of South America, he became increasingly depressed and lonely, eventually retreating to his cabin and consolidating his fantasies in a rambling 25,000-word philosophical treatise before jumping overboard. His body was never found.

What message can we take from these stories of endurance and despair? The obvious one is that we are, as a rule, considerably diminished when disengaged from others. Isolation may very often be the “sum total of wretchedness”, as the writer Thomas Carlyle put it.

However, a more upbeat assessment seems equally valid: it is possible to connect, to find solace beyond ourselves, even when we are alone. It helps to be prepared, and to be mentally resilient. But we shouldn’t underestimate the power of our imagination to knock over prison walls or even penetrate icy caves.

Editor's Note: Michael Bond is the author of The Power of Others (Oneworld Publications) BBC