But psychologists have demonstrated it's possible to implant memories.
"In my research we plant false memories in the minds of people in order to study the process," she said. "There have been hundreds of cases … where people have gone into therapy and were led to believe they were molested."
It's a problem that emerged in the '80s and '90s, according to the False Memory Foundation, an organization founded in 1992 after a spate of cases where adults claimed to have uncovered "repressed memories" of childhood sexual abuse during therapy sessions. The revelations, however, weren't true.
"They were just exploding at that time," said False Memory Foundation co-founder Pamela Freyd, adding that the cases often involved inpatients participating in both hypnosis and support groups while on medication.
Chris Barden, a psychologist and attorney based in Minnesota was at the helm of many of those cases.
"During the 1990s I conducted more lawsuits against 'recovered memory' therapists than, I believe, any other lawyer in the world … for a total near 300 in over 30 states," he told ABCNews.com. "I won all but one of them."
The False Memory Foundation website states false memories "can result from the influence of external factors, such as the opinion of an authority figure or information repeated in the culture. An individual with an internal desire to please, to get better or to conform can easily be affected by such influences."
For intelligent, creative people with imaginations, Freyd said, "it may be easier for them to conjure up the kinds of images that develop in this kind of environment." But anyone seeking therapy is already in a vulnerable position, she added, and susceptible to persuasion.
"You believe the person you are seeing is an expert who will help you return to normal, you are going to try to do what this expert says needs to be done," said Freyd. "And if an expert says you need to recover memories, people who want to get better or be sure they're doing what the doctor says will work in that direction."
Steven Lynn, a memory expert and professor of psychology at Binghamton University in New York, told ABCNews.com it's possible to implant "all kinds of things."
"There's research showing you can implant memories of witnessing a demonic possession," he said.
Schwartz denied having implanted Nasseff's memories, but he did say he practices exposure therapy, which is typically used as treatment for people who have PTSD, according to Lynn.
"The idea is that you present the person with imagined themes that have occurred in the past that tend to bring forth anxiety and symptoms of post traumatic stress disorder," Lynn said. "So by repeating exposure to the theme people learn how to not be so afraid of the situation they were formerly fearful of."
Exposure therapy can yield positive results in the right setting. But if someone has not actually been exposed to the traumatic event they're asked to re-imagine, exposure therapy can have a much different effect, Loftus said.
"If you take a group of women who have been raped and have them contemplate their legitimate rape experience then pretty soon many of them will be able to think about it without feeling as much emotion and pain," said Loftus. "But if you're exposing somebody to something that didn't happen then something completely different is going on."