Humans are hardwired to interact with others, especially during times of stress. On the other hand, when we go through a trying ordeal alone, a lack of emotional support and comradeship can increase our anxiety and hinder our ability to cope.

This message is forcefully driven home in the newly released thriller “Shut In.” Naomi Watts plays a widowed child psychologist who lives in isolation in rural New England with her son, who is comatose and bedridden as the result of an automobile accident. Snowed in and withdrawn from the outside world, Watts’ character descends into a desperate existence. It soon becomes difficult for her to distinguish the phantasms of her imagination from the reality of the creepy goings-on in her apparently haunted house.

“Shut In,” of course, isn’t the first movie to use isolation as a vehicle for madness. The characters played by Jack Nicholson in “The Shining” and Tom Hanks in “Castaway” found themselves in similar predicaments. Although movies like “Shut In” are fictional, the toll on the protagonist’s psyche from being so alone for so long is based on the science of social isolation.

The importance of human connection

Yes, other people can be irritating. But they are also our greatest source of comfort, and an impressive amount of psychological research underscores the importance of human contact.

Rejection by others psychologically wounds us more deeply than almost anything else, and research by neuroscientists reveals that ostracism can lead to feeling actual physical pain. Other studies confirm that loneliness isn’t good for anyone’s health. It increases levels of stress hormones in the body while leading to poor sleep, a compromised immune system and, in the elderly, cognitive decline. The damage that solitary confinement inflicts on the mental health of prison inmates has also been well-documented.

Alone in an unchanging environment, the sensory information available to us and the ways in which we process it can change in unpredictable ways. For example, we normally spend most of our time attending to and processing external stimuli from the physical world around us. However, monotonous stimulation from our surroundings may cause us to turn our attention inward – within ourselves – which most of us have much less experience handling.

This can lead to a profoundly altered state of consciousness. We may begin to question what’s going on in our surroundings; Is that creaking sound upstairs just an old house pushing back against the wind, or is it something more sinister? This ambivalence leaves us frozen in place, wallowing in unease, especially if we’re alone. When we’re uncertain, the first thing we usually do is to look to the reactions of others to figure out what is going on. Without others with whom to share information and reactions, ambiguity becomes very hard to resolve. When this happens, our mind may quickly race to the darkest possible conclusions.

Unpleasant things can also happen when small groups of people experience isolation together. Much of what we know about this phenomenon has been gathered from observing the experiences of volunteers at research stations in Antarctica, especially during the “wintering-over” period.

The extreme temperatures, long periods of darkness, alien landscapes and severely reduced sensory input created a perfect natural laboratory for studying the effects of isolation and confinement. The volunteers experienced changes in appetite and sleep patterns. Some stopped being able to accurately track the passage of time and lost the ability to concentrate. The boredom from being around the same people, with limited sources of entertainment, ended up causing a lot of stress. Everyone else’s mannerisms became a grating, annoying and inescapable source of torment.

Seeing ghosts

But perhaps the strangest thing that can happen to someone in isolation is the experience of the “sensed presence,” or the feeling that another person or even a supernatural being is with us.

Sensed presences usually appear in environments with static physical and social stimulation – in other words, when you’re by yourself in a quiet, remote place, just like Naomi Watts’ character in “Shut In.” Low temperature and high levels of stress are also common ingredients.

Some of the most compelling descriptions of sensed presences come from lone sailors, mountain climbers and arctic explorers who have experienced hallucinations and out-of-body experiences. In one amazing 1895 incident, Joshua Slocum, the first person to circumnavigate the globe in a sailboat singlehandedly, said he saw and spoke with the pilot of Christopher Columbus’ ship “The Pinta.” Slocum claimed that the pilot steered his boat through heavy weather as he lay ill with food poisoning.

The vividness of a presence can range from a vague feeling of being watched to seeing a seemingly real person. It could be a god, a spirit, an ancestor or a personal acquaintance. A famous example occurred in 1933, when British explorer Frank Smythe attempted to climb Mt. Everest alone. He became so convinced that someone else was accompanying him on his climb that he even offered a piece of cake to his invisible climbing partner.

Possible explanations for a sensed presence include the the movement of boats (if sailing solo) and atmospheric or geomagnetic activity. Stress, lack of oxygen, monotonous stimulation or a buildup of hormones can trigger changes in brain chemistry that induce altered states of consciousness. There’s actually exciting new evidence from a research group led by neuroscientist Olaf Blanke demonstrating that stimulating specific brain regions can trick people into feeling the “presence” of a ghostly apparition.

Although sensed presences are most frequently reported by people in weird or dangerous places, it’s not unreasonable to assume that such experiences can happen in more mundane surroundings. For example, people who have lost a loved one may shut themselves off from the outside world and rarely leave their homes. The loneliness and isolation, coupled with high levels of stress and unchanging sensory stimulation, might very well produce the same biological conditions that could trigger a “visit” from the recently departed. Studies indicate that almost half of widowed elderly Americans will report having hallucinations of their dead spouse. These experiences seem to be a healthy coping mechanism and a normal part of grieving.

What might all of this say about the way we’re hardwired?

It’s clear that meaningful connection to other people is as essential to health as the air we breathe. Given that prolonged periods of social isolation can crack even the hardiest of individuals, perhaps in the absence of actual human contact our brains may manufacture social experiences – a last-ditch attempt to preserve our sanity.