What would happen if you cut yourself off from the hurly-burly of life with just your own thoughts for company? A time of mental refreshment? Hardly. Studies have shown that for people living on their own, particularly older people, long-term isolation brings increased stress and physical symptoms such as higher blood pressure.

Now, a new televised experiment reveals how badly the brain is affected if isolation is complete and there is no sensory stimulation. It can take just hours for us to become more forgetful, worse at problem-solving, worse at finding words and, perhaps most worrying of all, more open to suggestion from other people. The findings may have implications for how we bring up children, look after the elderly and treat prisoners.

Next week’s Horizon on BBC Two recreates an experiment in sensory deprivation so controversial that it hasn’t been conducted for 40 years. Six volunteers were observed as they spent 48 hours completely isolated in pitch-black rooms, unable to see or hear anything. These are the sort of conditions endured by hostages such as Brian Keenan, who was isolated for eight months during his four-year captivity in Beirut, which ended in 1990.

Similar experiments were held in the 1950s, after thousands of American and Canadian prisoners of war had been held in conditions of sensory deprivation during the Korean War. Prompted by frequent accounts of PoWs seeming to have become “brainwashed” and taking on the views of their captors, North American psychologists examined how isolation affected the minds of volunteers. The experiments were closed down because they were deemed too cruel. But now the psychologist Ian Robbins – a professor at the University of Surrey and a specialist in supporting victims of torture, who has treated British detainees from Guantanamo Bay on their release – has reconstructed some of the sensory deprivation experiments in Horizon, but only for short periods, which are unlikely to result in long-term effects for the volunteers.

The volunteers soon began to hallucinate

Before being isolated, the volunteers underwent tests of visual memory (reproducing a complex drawing); information processing (filtering out confusing information); verbal fluency (naming words starting with a certain letter); and suggestibility (how likely they were to accept something their questioner said at face value, without pointing out that it was wrong). Then they spent two days and nights in isolation.

Two of the participants coped well, sleeping through much of the period. All found it profoundly boring; most found it distressing. One young woman became convinced that her sheets were wet even though, when she checked, they were found not to be. Most of the volunteers started pacing their small rooms like caged animals during the second day and felt less and less safe as time went on. Three experienced auditory and visual hallucinations – snakes, piles of oyster shells, tiny cars, zebras.

“It was weird,” said Mickey, a postman. “I started to imagine things; a load of fighter planes buzzing round, a swarm of mosquitoes. I thought the room was taking off at one time. That was frightening.”

Conducting the same tests again, when the “prisoners” were gratefully released after 48 hours, Professor Robbins found that their ability to do even the simplest tasks had deteriorated. Mickey’s memory capacity fell by 36 per cent. All the subjects had trouble thinking even of one or two words beginning with “F”. And all four of the men (though interestingly not the women) were markedly more suggestible.

It’s the last of these findings that Professor Robbins thinks has an immediate social and political relevance. “People being held for questioning in police stations, for example, may be treated humanely, but they get virtually no sensory input,” he says. “If the detention is for short periods of time, I don’t think that’s a problem, but there is talk of extending the period of time for which people can be held on suspicion of terrorist offences. And if people are indeed more suggestible, the longer they are held in isolation, the more that must raise questions about the reliability of their evidence.”

Exactly why people’s brains can be affected so radically by a short spell of isolation is still not fully understood, but Professor Robbins believes that the cells that connect nerve cells and help them to communicate, called dendrites, may lose some of their connectivity if not continually stimulated. There’s certainly evidence of the opposite, that stimulating the brain increases the number of connections. Studies on people with brain injuries have shown that mental stimulation increases the number of dendritic connections that form.

Long periods in solitary cause psychosis

Other studies have shown subtle physical changes to the brain when mammals become isolated. Research from the University of Illinois, published late last year, showed that the enzymes needed to produce a stress-reducing brain hormone drops significantly when mice are isolated. This can lead to aggression as well as anxiety. There is an overwhelming body of evidence that long periods of solitary confinement causes problems such as psychosis in prisoners, and that unmarried people who live fairly socially isolated lives become more ill, die earlier, and have more mental illness. Conversely, there is evidence that older people can maintain the health of their brains for longer if they keep them stimulated by solving problems.

“The brain is an amazing processor for information,” says Professor Robbins. But in the absence of information coming in, he says, the brain develops its own information inputs, which is why hallucinations begin and why captives’ understanding of the world is changed.

Sarah Jane Blakemore, a neuroscientist, emphasises that little reliable research on long-term sensory deprivation in adults has been conducted until now. And she emphasises that the brain has a remarkable capacity to bounce back after short-term change: “Most of the effects observed after 48 hours will be transient.” Nonetheless, studies on children suggest that longer periods of sensory deprivation can severely affect brain development. Brain scanning studies at Baylor College of Medicine in the US have found notable differences in brain structure between three-year-old children who have long-term sensory neglect – whether it be through physical isolation or visual birth defects – and normal children. Their brains are smaller and develop abnormally.

So why do we love isolation tanks?

Sensory deprivation experiments all seem to point to the importance of daily interaction with others, of keeping our ears, eyes and problem-solving abilities constantly exercised, even if our natural inclinations are to withdraw into solitude. Yet the findings also raise other questions. If social and sensory isolation is so bad for us, how come many people find such solace in isolation and believe in the therapeutic value of isolation tanks? The crucial factors seem to be how long, and how voluntary, the isolation.

The concept of sensory-deprivation tanks was invented in the 1950s, when the neuroscientist John Lilly discovered that cutting off all stimuli could induce a deep state of relaxation hard to achieve in normal life, and in which the brain began to free-associate creatively. Since then, Dr Peter Suedfeld, a Canadian psychologist, has conducted experiments suggesting that short-term sensory deprivation can reduce stress and even help people to give up smoking.

The short-term benefits may arise because brainwaves appear to change from the waking alpha and beta forms, to theta waves, which normally occur in sleep. But a flotation tank session normally lasts only an hour. The brain would respond differently over several hours, transferring from a state of relaxation to one of anxiety.

“It’s a very different matter being in a flotation tank when you know you just have to push a button to get out, to being isolated with no end in sight,” says Professor Robbins. “Getting stimulation is how the brain stays healthy.”

The key seems to be that as long as we have the free will to seek out either isolation or stimulation when we need it, the brain will largely self-regulate its health. The real problems come for those who have less say in what they do – children, older people in care homes and prisoners. And it is for their sake that this new area of research is worth pursuing once again.

Alone, BBC Two, Tuesday, 9pm

Solitary facts

Early experiments Prisoners at a Philadelphia jail were studied in 1829, in the belief that locking them in a cell with nothing but a bible would make them repent. Many went insane.

Lonely old age 730,000 elderly people don’t leave their homes more than once a week says Help the Aged.

Heart risk A University of California study suggests that social isolation increases the risk of heart conditions in older people.

Addiction treatment Research in the 70s and 80s indicated that short spells of sensory deprivation may help people change eating, drinking and smoking habits. Source: Times database

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