Two remarkable cases came to light last year when women escaped from captivity after being held for many years.
In Cleveland, Ohio, three young women, Gina DeJesus, Michelle Knight, Amanda Berry, and her six-year-old daughter, were rescued by a neighbour. He heard one of them screaming as she ran toward him, having managed to exit her captor's house after a decade in captivity.
The women were held in a house in a poor area but the house itself was not unusual when compared to the other properties.
In November, three women in their 50s and 60s were rescued from an ordinary house in South London where they were allegedly held captive for 30 years.
There have been others in the years before 2013 including two in Austria. One case involved Elizabeth Fritzl, who was held in an underground bunker beneath the family home and repeatedly raped by her father for more than 20 years. And an 80-year-old allegedly held his two daughters for more than 40 years in the family home in St Peter am Hart, near where Hitler was born. These victims also escaped.
One very famous shorter-term victim was heiress Patty Hearst who was kidnapped by a left-wing terrorist group in 1974. She was held for two months in a state of sensory deprivation in a closet, blindfolded, repeatedly raped and threatened with death. She allegedly had two baths in that period.
Hearst then declared her commitment to the cause of her captors and, after she participated in a bank robbery, was arrested and sent to prison.
In 1973 a woman was held captive during a bank siege in Stockholm. After the six-day siege, she refused to give evidence against her captors and developed an intimate relationship with one of them.
Such entrapment is unimaginably traumatic and the question that people ask is -- how do individuals survive the threats of death that constantly pervade such situations?
Two psychiatrists who specialise in "traumatic entrapment", Dr Chris Cantor from the University of Queensland and Dr John Price from London believe that in these rare and unusual circumstances an appeasement reaction sets in to ensure survival.
In an interview on the Royal College of Psychiatrists website, Dr Cantor says it explains the Stockholm Syndrome.
He argues that such protective reactions are hardwired into our genes.
The reaction to preserve one's life occurs against a hostile and dangerous environment created by the captors. This includes sensory deprivation such as blindfolding, isolation, poor and dirty living conditions, repeated threats, humiliation and a sense of powerlessness.
The captives thus feel the need to protect themselves and avoid the wrath of the captors. This activates conciliation, submission and appeasement as a survival tool.
As a method of self-preservation it is also seen in victims of domestic violence whom they observe are sometimes reconciled with their abuser and behave flirtatiously and submissively towards him. By turning to the dominant person for comfort, the victim de-escalates the situation. And of course in the closed environment of a kidnap situation there may only be the dominant oppressors to turn to, according to Cantor.
This is one area where conclusions from animal studies may also provide information than can be applied to humans. For example monkeys and apes, after being attacked return to their attacker for comfort and safety -- this is known as reverted escape.
Dogs, if attacked, save themselves by turning over on their backs like puppies. This makes the trauma of captivity so difficult to treat because many will have resorted to appeasement and they will have accepted some blame for their captivity.
Cantor and Price argue that appeasement has an evolutionary basis and that it is carried in our genes.
They contend that for this reason, those who engage in it should not be punished when they resort to criminal or terrorist behaviours in support of their captors.
In 1976 Patty Hearst was sentenced to 35 years in prison for her participation in the bank robbery with her terrorist captors, The Symbionese Liberation Army.
After two years she was released and was granted a full pardon from President Clinton on January 20, 2011.