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.