In Zero Dark Thirty, Jessica Chastain plays "Maya," a CIA officer who, at one point, treats a detainee to a sumptuous dinner to reward him for sharing critical information that she says saved American lives. The thing is, the detainee doesn't remember telling his captors anything. But weak in mind and body, after several sleepless days and nights of torture, he accepts what Maya says as the truth. This is gaslighting.

The term itself was popularized by the 1944 film Gaslight, an adaptation of the 1939 play Angel Street. In the film, starring Charles Boyer and Ingrid Bergman, "Gregory," played by Boyer, maintains that a gaslight his wife "Paula" (Bergman) sees growing dim then brightening is in fact steady. This small deception is followed by countless others. Paula initially protests her husband's accusations about her "forgetfulness," but in time she questions her every action and memory. In reality, her husband Gregory is plotting to have her committed to an asylum so that he can take her inheritance.

In the book Gaslighting, the Double Whammy, Interrogation and Other Methods of Covert Control in Psychotherapy and Analysis, the late forensic psychiatrist Theodore Dorpat defines gaslighting as a situation in which one individual "attempts to exert control over the feelings, thoughts or activities of another." According to Dorpat, the gaslighting behavior itself is covert — neither "directly hostile" nor "intimidating."

"In order to be effective, gaslighting depends on first convincing the victim that his thinking is distorted and secondly persuading him that the victimizer's ideas are the correct and true ones," writes Dorpat.

In every gaslighting situation there must be a gaslighter, the agent of the abuse, and a gaslightee, his or her target. "Over time you [the gaslightee] begin to feel like you don't know your own mind or you don't know your own reality. Worse than that, you've allowed someone else to define it for you," says Dr. Robin Stern, author of The Gaslight Effect and a research scientist at the Yale Center for Emotional Intelligence.â€¨

In the 2001 French film Amelie, the film's namesake conceives a plan to gaslight a neighborhood grocer for bullying a mentally challenged employee. First, she sneaks inside the grocer's home. Then she replaces his slippers with duplicates in a smaller size, reverses door handles with knobs and swaps his toothpaste with foot cream. In a final triumphant act, she resets the speed dial button on the grocer's telephone to dial a psychiatric institution instead of his mother's home.

Of course, more subtle and prosaic instances of gaslighting abound. In a typical example, one friend makes another friend wait for over an hour every time they meet for drinks. When the person waiting shows that he or she is upset, the tardy friend asks how someone can be so sensitive.

When gaslightees defend their own feelings or character they are dismissed by their gaslighters as crazy, irrational, or uptight. "It's like a magic trick, a sleight of hand. Let me focus your attention here rather than there," Stern told me. "Maybe you are sensitive, but what does that have to do with the other person being late?"

The first stage in gaslighting is disbelief. At this point, a gaslightee views any disagreement as minor, silly, or forgettable. In the second stage, defense, the gaslightee has begun to second-guess himself. The third stage is depression. The gaslightee actually wants to prove the gaslighter right. Then at least he or she can find a way to earn the approval of the gaslighter.

In Stern's experience, the gaslightees are more often women and the gaslighters are frequently, but not always, men. "The women rather than saying 'you can't talk to me like that' will try harder. 'Let me make that meatloaf again. Let me put my outfit together again.'"

Common signs of the gaslight effect are feeling bewildered or confused, suffering from fitful sleep or nightmares, and an inability to remember the particulars of situations involving the gaslighter. Avoiding speaking about a particular relationship with other friends and feeling a loss of happiness are also strong indicators of a gaslighting relationship.

At the core of the worst cases is the idea that individuals feel respect, love, or admiration for their gaslighters. "When we idealize the gaslighter — when we want to see him as the love of our life, an admirable boss, or a wonderful parent — then we have even more difficulty sticking to our own sense of reality," says Stern.

The more conscious gaslighting victims are of these power plays in their early stages, the easier it is to disengage or even to end that relationship. Each case is different, but the first and most important step is to stop trying to gain the gaslighter's approval.